Theoretical and applications aspects of optoelectronics technology are examined in an introduction for engineering students and practicing engineers. Chapters are devoted to the fundamental principles of optics and optoelectronics, optical coherence and polarization, semiconductor light sources, optical fibers, nonlinear effects in optical fibers, optical-fiber cables and connectors, and fiber-optic components. Consideration is given to integrated optics, fiber-optic telecommunication systems, fiber sensors and sensor networks, optical remote sensing, optical information processing, guided-wave signal processing, and optical-disk storage systems.

This article reviews my new optical fiber sensing (OFS) research activities in China for the last ten years at Chongqing University and University of Electronic Science and Technology of China, since I returned from UK in 1999. The research progress in long period fiber gratings (LPFGs), distributed fiber sensing systems and microfiber sensors is introduced. For LPFGs, the processing method with high-frequency CO2 laser pulses types of LPFGs fabricated and the related applications for both optical sensing and optical communication are described. For distributed fiber sensing systems, the fiber-optic polarization optical time domain reflectometer (POTDR), fiber-optic phase-sensitive optical time domain reflectometer (?-OTDR) and Brillouin optical time-domain analyzer (BOTDA) are developed, respectively. For microfiber sensors, we mainly focus on the knot resonator and its application for sensing of the refractive index and acceleration, etc.

A brief review on suspended-core fibers for sensing applications is presented. A historical overview over the previous ten years about this special designed microstructure optical fiber is described. This fiber presents attractive optical properties for chemical/biological or gas measurement, but it can be further explored for alternative sensing solutions, namely, in-fiber interferometers based on the suspended-core or suspended-multi-core fiber, for physical parameter monitoring.

Electron beam lithography (EBL) was used to directly pattern periodic gold nanodot arrays on optical fiber tips. Localized surface plasmon resonance of the E-beam patterned gold nanodot arrays on optical fiber tips was utilized for biochemical sensing. The advantage of the optical fiber based locali...

Taper Ratio. 0.35. 1.0. Dihedral ..... The HUD, with the combiner integrated into the ..... fibers will be used for data transmission to take ad- vantage ... sensors. Optical fibers intended for sensing applications will be standard fiberoptic. #ass.

The combination of fiber optics with nano-structure technologies and sensitive thin films offers great potential for the realization of novel sensor concepts. Miniatured optical fiber sensors with thin films as sensitive elements could open new fields for optical fiber sensor applications. Thin films work as sensitive elements and transducer to get response and feedback from environments, in which optical fibers are employed to work as signal carrier. This article presents some research work conducted at the National Engineering Laboratory for Optical Fiber Sensing Technologies in recent years. Concrete examples are: Pd/WO3 co-sputtered coating as sensing material for optical hydrogen sensors shows robust mechanical stability and meanwhile good sensing performance; TbDyFe magnetostrictive coating directly deposited on fiber Bragg grating (FBG) demonstrates its possibility of miniature optical magnetic field/current sensors, and 40-pm shift of the FBG wavelength happens at a magnetic field order of 50 mT.

The present conference on embedded fiber-optics incorporating 'smart' structural systems and structural surfaces discusses topics in the nature and current status of university- and government-sponsored smart-structure development programs, manufacturing and cure-monitoring for composite smart structures, smart-structure damage assessment, smart-structure actuators, and smart-structure sensors and components. Attention is given to fiber-optic sensor selection, the optical properties of curing epoxies, the automated production of smart structures, damage-detection in composites with embedded fiber-optic interferometers, fiber-optic strain and impact sensors, dynamically-tunable smart composites, smart structures incorporating artificial neural networks, active structural acoustic control with smart structures, and fiber-optic shape sensing for flexible structures.

This work addresses the development and assessment of a fiber optical viscometer using a simple and low-cost long-period fiber grating (LPFG) level sensor and a capillary tube mechanism. Previous studies of optical viscosity sensors were conducted by using different optical sensing methods. The prop...

We describe the results of a study of the performance characteristics of a monolithic fiber-optic shape sensor array. Distributed strain measurements in a multi-core optical fiber interrogated with the optical frequency domain reflectometry technique are used to deduce the shape of the optical fiber; referencing to a coordinate system yields position information. Two sensing techniques are discussed herein: the first employing fiber Bragg gratings and the second employing the intrinsic Rayleigh backscatter of the optical fiber. We have measured shape and position under a variety of circumstances and report the accuracy and precision of these measurements. A discussion of error sources is included.

Fiber loop ringdown (FLRD) utilizes an inexpensive telecommunications light source, a photodiode, and a section of single-mode fiber to form a uniform fiber optic sensor platform for sensing various quantities, such as pressure, temperature, strain, refractive index, chemical species, biological cells, and small volume of fluids. In FLRD, optical losses of a light pulse in a fiber loop induced by changes in a quantity are measured by the light decay time constants. FLRD measures time to detect a quantity; thus, FLRD is referred to as a time-domain sensing technique. FLRD sensors have near real-time response, multi-pass enhanced high-sensitivity, and relatively low cost (i.e., without using an optical spectral analyzer). During the last eight years since the introduction of the original form of fiber ringdown spectroscopy, there has been increasing interest in the FLRD technique in fiber optic sensor developments, and new application potential is being explored. This paper first discusses the challenging issues in development of multi-function, fiber optic sensors or sensor networks using current fiber optic sensor sensing schemes, and then gives a review on current fiber optic sensor development using FLRD technique. Finally, design perspectives on new generation, multi-function, fiber optic sensor platforms using FLRD technique are particularly presented. PMID:22408471

A fiber optic vibration sensor utilizes two single mode optical fibers supported by a housing with one optical fiber fixedly secured to the housing and providing a reference signal and the other optical fiber having a free span length subject to vibrational displacement thereof with respect to the housing and the first optical fiber for providing a signal indicative of a measurement of any perturbation of the sensor. Damping or tailoring of the sensor to be responsive to selected levels of perturbation is provided by altering the diameter of optical fibers or by immersing at least a portion of the free span length of the vibration sensing optical fiber into a liquid of a selected viscosity.

This work presents a novel fiber-optic sensing system, capable of monitoring debris flows or other natural hazards that produce ground vibrations. The proposed sensing system comprises a demodulator (BraggSCOPE, FS5500), which includes a broadband light source and a data logger, a four-port coupler and four Fiber Bragg Grating (FBG) accelerometers. Based on field tests, the performance of the proposed fiber-optic sensing system is compared with that of a conventional sensing system that includes a geophone or a microphone. Following confirmation of the reliability of the proposed sensing system, the fiber-optic sensing systems are deployed along the Ai-Yu-Zi and Chu-Shui Creeks in Nautou County of central Taiwan for monitoring debris flows. Sensitivity test of the deployed fiber-optic sensing system along the creek banks is also performed. Analysis results of the seismic data recorded by the systems reveal in detail the frequency characteristics of the artificially generated ground vibrations. Results of this study demonstrate that the proposed fiber-optic sensing system is highly promising for use in monitoring natural disasters that generate ground vibrations. PMID:10426990

Fundação para a Ciência e a Tecnologia (FCT) , Optical sensors have hit their maturity and a new kind of systems is being developed. This paper deals with the development of a new sensing structure based on polymeric foils and optic fiber sensors, namely the Fiber Bragg Grating sensors. Sensor integrat...

Bio-molecular recognition is detected by the unique optical properties of self-assembled gold nanoparticles on the unclad portions of an optical fiber whose surfaces have been modified with a receptor. To enhance the performance of the sensing platform, the sensing element is integrated with a micro...

Recent advances in materials science have resulted in a proliferation of flexible structures for high-performance civil, mechanical, and aerospace applications. Large aspect-ratio aircraft wings, composite wind turbine blades, and suspension bridges are all designed to meet critical performance targets while adapting to dynamic loading conditions. By monitoring the distributed shape of a flexible component, fiber optic shape sensing technology has the potential to provide valuable data during design, testing, and operation of these smart structures. This work presents a demonstration of such an extended-range fiber optic shape sensing technology. Three-dimensional distributed shape and position sensing is demonstrated over a 30m length using a monolithic silica fiber with multiple optical cores. A novel, helicallywound geometry endows the fiber with the capability to convert distributed strain measurements, made using Optical Frequency-Domain Reflectometry (OFDR), to a measurement of curvature, twist, and 3D shape along its entire length. Laboratory testing of the extended-range shape sensing technology shows

The present invention relates to lasers and particularly to a diode-pumped, fiber laser doped with thulium activator ions for producing an output CW laser emission at a wavelength of substantially 2.3 microns. In low power applications, such as in telecommunications and in medical and sensing applications, the use of fiber lasers is becoming more and more important. In a typical fiber laser a rare earth, such as erbium, neodymium, terbium or praseodymium, is doped into the core of an optical fiber to provide an active gain medium for the fiber laser. Typically, the optical fiber is comprised of silica.

Fiber-optic sensors are widely used and researched in-depth. Interferometric fiber optic sensor is an important category of fiber optic sensor because of its high sensitivity. However, polarization-induced fading phenomena always appear in the output of sensors which constructed of low-birefringence single mode fibers. In this paper, we firstly give the structure of a fiber-optic sensor based on M-Z fiber optic interferometer. And we use polarization optics to study the light state in this sensor. Taking the polarization state of input light in fiber-optic interferometer is random we calculate the Jones vector of the output light. To study the polarization fading phenomena we calculate the intensity of output light. We caculate the degree of polarization fading by computer software. The result shows that sensing signal will completely vanish. Thus we can't get steady sensing signal and we must use depolarization fading technology. We give a simple structure of a polarizationinsensitive optical fiber sensor. Two Faraday rotator mirrors (FRM) are added into Michelson optical fiber interferometer to improve the visibility. We also use polarization optics to study the output light of this structrue. Theoretical analysis and experimental study indicates that this convenient method can improve visibility to 1. The feature of the method is convenient, accuracy and practical. And it can apply to various kinds of complex construction.

Infrared optical fibers are finding a number of applications including laser surgery, remote sensing, and nuclear radiation resistant links. Utilizing these fibers in space-based structures is another application, which can be exploited. Acoustic and thermal sensing are two areas in which these fibers could be utilized. In particular, fibers could be embedded in IM7/8552 toughened epoxy and incorporated into space structures both external and internal. ZBLAN optical fibers are a candidate, which have been studied extensively over the past 20 years for terrestrial applications. For the past seven years the effects of gravity on the crystallization behavior of ZBLAN optical fiber has been studied. It has been found that ZBLAN crystallization is suppressed in microgravity. This lack of crystallization leads to a fiber with better transmission characteristics than its terrestrial counterpart.

Fiber-optic sensors, especially fiber Bragg grating (FBG) sensors are very attractive due to their numerous advantages over traditional sensors, such as light weight, high sensitivity, cost-effectiveness, immunity to electromagnetic interference, ease of multiplexing and so on. Therefore, fiber-optic sensors have been intensively studied during the last several decades. Nowadays, with the development of novel fiber technology, more and more newly invented fiber technologies bring better and superior performance to fiber-optic sensing networks. In this paper, the applications of some advanced photonic technologies including fiber lasers and microwave photonic technologies for fiber sensing applications are reviewed. FBG interrogations based on several kinds of fiber lasers, especially the novel Fourier domain mode locking fiber laser, have been introduced; for the application of microwave photonic technology, examples of microwave photonic filtering utilized as a FBG sensing interrogator and microwave signal generation acting as a transversal loading sensor have been given. Both theoretical analysis and experimental demonstrations have been carried out. The comparison of these advanced photonic technologies for the applications of fiber sensing is carried out and important issues related to the applications have been addressed and the suitable and potential application examples have also been discussed in this paper. PMID:22778591

Microstructured optical fibers are increasingly used in optical fiber sensing applications such as for example optical fiber based structural health monitoring. In such an application the fiber may experience substantial mechanical loads and has to remain functional during the entire lifetime of the structure to be monitored. The resistance to different types of mechanical loads has therefore to be characterized in order to assess the maximum stress and strain that a fiber can sustain. In this paper we therefore report on the extensive set of tensile tests and bending experiments that we have conducted both on microstructured optical fibers with an hexagonal air hole lattice and on standard optical fibers. We use Weibull statistics to model the strength distribution of the fibers and we follow a fracture mechanics approach in conjunction with microscopic observations of the fractured end faces to study crack initiation and propagation in both types of fibers. We show that the failure strain of microstructured fibers is about 4.3% as obtained with tensile tests, compared to 6.7% for reference fibers. Although the mechanical strength of microstructured optical fibers is lower than that of the standard fibers it is still adequate for these fibers to be used in many applications.

The progress of optical fiber technology for communications has induced an interest in, among others, the sensing of a wide range of physical, and chemical quantities. Any application of optical fibers that are crucial for communication are significant for sensing, e.g. small dimension, insulating materials, immunity to high voltage field etc. In the present paper basic points of optical fiber sensing are summarized. It is noted optical fiber sensors come in two forms, intrinsic and extrinsic. In the former the fiber itself works as sensing element, in addition to data transmission lines. In an intrinsic sensor, a single fiber transmits the light from the source to the detector and the light is modulated while it is in the fiber. On the other hand, in the extrinsic sensor, the light leaves the input fiber to be modulated before being collected by the second output fiber. Characteristic of the light that can be modulated are amplitude, phase, polarization, and wavelength. The paper describes the modulation in some details. (author)

In this research, the key technologies on the distributed fiber optic sensor system are developed. A high power pulse laser driver is designed. The optical coupler for discriminating backscattered optical signal and splicing sensing optical fiber, and signal precessing electronics for receiving backscattered optical signal are also developed. By using the parallel processing algorithms and EPLD technique, a high speed signal averaged which is used for improving the signal to noise ratio is developed. A communication software used for sending received optical sensing signal to personal computer and a graphic software used for displaying the measurement result on personal computer monitor are developed. Test of distributed fiber optic sensor system was made along 1.1 km optical fiber. Experimental results show that optical output power of the backscattering light wave exponentially decays as the time axis approaches to the fiber end point. Since the output power of backscattered signal is very weak, the high speed signal averaged which is used for improving the signal to noise ratio and parallel processing algorithm which is used for reducing the measuring time of distributed fiber optic sensor system should be adapted. In the near future, developed technologies will be applied to new application system about distributed fiber optic sensor system. (author). refs., figs., tabs.

Optical fibers and specialty waveguides are the bases of the majority of today's telecommunication, biomedical, sensing, and light-delivery applications. Modal analysis plays an important role in optimizing the optical performance of these fibers when they are integrated with optical systems. We present a full vectorial modal theoretical analysis of specialty cylindrical symmetric fibers with arbitrary index profiles, using a staircase approximation and scattering matrix approach with no constraints on the refractive index profile. We demonstrate the generality of this method by investigating the modal characteristics of two specialty fibers: graded-index fiber and concentric-shell multicore fiber. The calculated modal effective indices for the graded-index fiber are compared with those calculated by the WKB method, stressing the main differences between the scalar and vectorial approaches. Using the same approach, we calculate the Bragg grating response of a holographic grating written in the guiding regions of a concentric-shell fiber and compared them with experimental measurements. PMID:16676036

In this paper, a fiber optic sensor based on fiber Bragg grating (FBG) is employed to measure the ground vibrations which may be generated by earthquakes, debris flows, landslides, and rock impacts on the ground. The detected vibration signals were analyzed by both fast Fourier transform (FFT) and Gabor transform to obtain the frequency response. The performance of fiber optic sensor was examined and compared with the conventional ground vibration geophone sensor. From the results of field tests, the fiber optic sensor shows highly similarity with conventional geophone sensor for low frequency measurement. The fiber optic vibration sensing system presented in this research is appropriate for sensing ground vibration in the frequency ranges of 10-250 Hz. The sensor proved to be an alternative option for ground vibrations monitoring system.

The chemistry of sol-gel derived silica and refractive metal oxide has been systematically studied. Sol-gel processes have been developed for preparing porous silica and semiconductor metal oxide materials. Micelle/reversed micelle techniques have been developed for preparing nanometer sized semiconductor metal oxides and noble metal particles. Techniques for doping metal ions, metal oxides and nanosized metal particles into porous sol-gel material have also been developed. Optical properties of sol-gel derived materials in ambient and high temperature gases have been studied by using fiber optic spectroscopic techniques, such as fiber optic ultraviolet/visible absorption spectrometry, fiber optic near infrared absorption spectrometry and fiber optic fluorescence spectrometry. Fiber optic spectrometric techniques have been developed for investigating the optical properties of these sol-gel derived materials prepared as porous optical fibers or as coatings on the surface of silica optical fibers. Optical and electron microscopic techniques have been used to observe the microstructure, such as pore size, pore shape, sensing agent distribution, of sol-gel derived material, as well as the size and morphology of nanometer metal particle doped in sol-gel derived porous silica, the nature of coating of sol-gel derived materials on silica optical fiber surface. In addition, the chemical reactions of metal ion, nanostructured semiconductor metal oxides and nanometer sized metal particles with gas components at room temperature and high temperatures have also been investigated with fiber optic spectrometric methods. Three classes of fiber optic sensors have been developed based on the thorough investigation of sol-gel chemistry and sol-gel derived materials. The first group of fiber optic sensors uses porous silica optical fibers doped with metal ions or metal oxide as transducers for sensing trace NH{sub 3} and H{sub 2}S in high temperature gas samples. The second group of fiber optic sensors uses sol-gel derived porous silica materials doped with nanometer particles of noble metals in the form of fiber or coating for sensing trace H{sub 2}, NH{sub 3} and HCl in gas samples at for applications ambient temperature. The third classes of fiber optic sensors use sol-gel derived semiconductor metal oxide coating on the surface of silica optical fiber as transducers for selectively sensing H{sub 2}, CH{sub 4} and CO at high temperature. In addition, optical fiber temperature sensors use the fluorescence signal of rare-earth metal ions doped porous silica optical fiber or the optical absorption signal of thermochromic metal oxide materials coated on the surface of silica optical fibers have also been developed for monitoring gas temperature of corrosive gas. Based on the results obtained from this project, the principle of fiber optic sensor techniques for monitoring matrix gas components as well as trace components of coal gasification derived syngas has been established. Prototype sensors for sensing trace ammonia and hydrogen sulfide in gasification derived syngas have been built up in our laboratory and have been tested using gas samples with matrix gas composition similar to that of gasification derived fuel gas. Test results illustrated the feasibility of these sensors for applications in IGCC processes.

Multi-core fiber (MCF) optic shape sensing offers the possibility of providing in-flight shape measurements of highly flexible aerospace structures and control surfaces for such purposes as gust load alleviation, flutter suppression, general flight control and structural health monitoring. Photogrammetric measurements of surface mounted MCF shape sensing cable can be used to quantify the MCF installation path and verify measurement methods.

Recently, many programs have been developed for simulation or analysis of the different parameters of light propagation in optical fibers, either for sensing or for communication purposes. In this paper, it is shown the COMSOL Multiphysics as a fairly robust and simple program, due to the existence of a graphical environment, to perform simulations with good accuracy. Results are compared with other simulation analysis, focusing on the surface plasmon resonance (SPR) phenomena for refractive index sensing in a D-type optical fiber, where the characteristics of the material layers, in terms of the type and thickness, and the residual fiber cladding thickness are optimized.

The development of new chemical and biosensing schemes has been a topic of great interest. In our laboratory, a portion of our work has centered on the use of sol-gels doped with fluorescent dyes as materials for forming small optical fibers used for sensing. We are currently working with pyrene-doped fibers for oxygen sensing and fluorescein-doped fibers to detect changes in pH. These schemes have shown great promise, however, several factors (e.g., cost, size, rigidity, response time, sensitivity) are associated with building practical sensors. It is also critical to understand the actual sol-gel composite gelation process in order to quantitatively determine the appropriate conditions for forming microsensor tips from these sol-gel materials. This presentation will focus on the construction of an inexpensive, micron-size fiber-optic sensor as well as a small flow-cell apparatus for the detection of various analytes. Also, the actual preparation of these sol-gel derived optical fibers will be discussed.

This report summarizes work to develop a novel distributed fiber-optic micro-sensor that is capable of detecting common fossil fuel gases in harsh environments. During the 32-month research and development (R&D) program, GE Global Research successfully synthesized sensing materials using two techniques: sol-gel based fiber surface coating and magnetron sputtering based fiber micro-sensor integration. Palladium nanocrystalline embedded silica matrix material (nc-Pd/Silica), nanocrystalline palladium oxides (nc-PdO{sub x}) and palladium alloy (nc-PdAuN{sub 1}), and nanocrystalline tungsten (nc-WO{sub x}) sensing materials were identified to have high sensitivity and selectivity to hydrogen; while the palladium doped and un-doped nanocrystalline tin oxide (nc-PdSnO{sub 2} and nc-SnO{sub 2}) materials were verified to have high sensitivity and selectivity to carbon monoxide. The fiber micro-sensor comprises an apodized long-period grating in a single-mode fiber, and the fiber grating cladding surface was functionalized by above sensing materials with a typical thickness ranging from a few tens of nanometers to a few hundred nanometers. GE found that the morphologies of such sensing nanomaterials are either nanoparticle film or nanoporous film with a typical size distribution from 5-10 nanometers. nc-PdO{sub x} and alloy sensing materials were found to be highly sensitive to hydrogen gas within the temperature range from ambient to 150 C, while nc-Pd/Silica and nc-WO{sub x} sensing materials were found to be suitable to be operated from 150 C to 500 C for hydrogen gas detection. The palladium doped and un-doped nc-SnO{sub 2} materials also demonstrated sensitivity to carbon monoxide gas at approximately 500 C. The prototyped fiber gas sensing system developed in this R&D program is based on wavelength-division-multiplexing technology in which each fiber sensor is identified according to its transmission spectra features within the guiding mode and cladding modes. The interaction between the sensing material and fossil fuel gas results in a refractive index change and optical absorption in the sensing layer. This induces mode coupling strength and boundary conditions changes and thereby shifts the central wavelengths of the guiding mode and cladding modes propagation. GE's experiments demonstrated that such an interaction between the fossil fuel gas and sensing material not only shifts the central wavelengths of the guide mode and cladding modes propagation, but also alters their power loss characteristics. The integrated fiber gas sensing system includes multiple fiber gas sensors, fiber Bragg grating-based temperature sensors, fiber optical interrogator, and signal processing software.

This paper describes the development of a fiber-optic chemical sensor based on the principle of competitive-binding fluorescence immunoassay. Rabbit immunoglobin G (IgG) is covalently immobilized on the distal sensing tip of a quartz optical fiber. The sensor is exposed to fluorescein isothiocyanate (FITC) labeled and unlabeled anti-rabbit IgG. The 488-nm line of an argon-ion laser provides excitation of sensor-bound analyte. This results in fluorescence emission at the optical fiber's sensing tip. Sensor response is inversely proportional to the amount of unlabeled anti-IgG in the sample. Limits of detection (LOD) vary with incubation time, sample size, and measurement conditions. For 10-/sup +/L samples, typical LOD are 25 fmol of unlabeled antibody in a 20-min incubation period. These results indicate that each fiber-optic fluoroimmunosensor can be constructed to perform a single sensitive, rapid, low-volume immunoassay, in in situ or benchtop applications.

We have experimentally implemented a multiplexible but compact fiber sensor system suitable for multipoint sensing of hydrogen gas leakage. By making dual cavities along an optical fiber and coating a palladium film only at the end of the fiber tip, the measurement errors induced by the optical source power fluctuation and the mechanical perturbation in the lead fiber could be compensated. By adjusting the length of the dual-cavity, the capability of multiplexing several hydrogen sensors could be achieved. The experiment results showed that the response speed of the sensor was increasing with temperature, but at a low temperature the response amplitude became large. PMID:21935185

Based on the force analysis, we establish a theoretical model to study the static pressure distribution of the fiber cable spool for the fiber optic guided missile (FOG-M). Simulations indicate that for each fiber layer in the fiber cable spool, the applied static pressure on it asymptotically converges as the number of fiber layers increases. Using the distributed fiber Bragg grating (FBG) sensing technique, the static pressure of fiber cable layers in the spool on the cable winding device was measured. Experiments show that the Bragg wavelength of FBG in every layer varies very quickly at the beginning and then becomes gently as the subsequent fiber cable was twisted onto the spool layer by layer. Theoretical simulations agree qualitatively with experimental results. This technology provides us a real-time method to monitor the pressure within the fiber cable layer during the cable winding process.

A new optical nuclear instrumentation system such as that in core power and temperature monitor using radiation-resistant optical fibers was demonstrated. Developed radiation-resistant optical fibers as a sensing component kept their good transmission characteristics even in a reactor irradiation. Optical fibers generated strong radio luminescence wavelength ranged 400 nm to 1400 nm with some of peaks and thermal radiation in infrared during irradiation in a core region of fission reactor. Intensities of radio luminescence were found to be directly proportional to the reactor power. Also, temperatures could be estimated by thermal radiation of Planck's law. The optical measuring method using optical fibers could be composed simple and convenient nuclear instrumentation system of the reactor power and temperature. (author)

Optical gas sensing performance of optical fibers coated with sputtered Pd/WO3 films was investigated for low concentration H2 sensing. This optical fiber H2 sensor was prepared by RF sputtering of WO3 on the tip of the multimode fiber at 260°C and subsequently depositing a Pd catalytic layer. Highly uniform nanotextured film, with individual crystallites having diameters in the range of 35-50 nm was observed. The sensing mechanism was based on the reflectance change of Pd/WO3 layers towards H2 reliant on the gasochromic effect. Under the conditions of different sensing layer thicknesses and different operating temperatures, full Vis-NIR spectra investigations were carried out during the sensor testing. It was found that the optical fiber H2 sensor coated with Pd/WO3 film show a remarkable optical reflectance response towards H2 concentrations as low as 0.06%. The optimum sensing layer thickness was 200 nm and the optimum operating temperature was found to be 100°C.

Microfiber-based Bragg gratings (MFBGs) are an emerging concept in ultra-small optical fiber sensors. They have attracted great attention among researchers in the fiber sensing area because of their large evanescent field and compactness. In this review, the basic techniques for the fabrication of MFBGs are introduced first. Then, the sensing properties and applications of MFBGs are discussed, including measurement of refractive index (RI), temperature, and strain/force. Finally a summary of selected MFBG sensing elements from previous literature are tabulated. PMID:23012522

Pacific Northwest Laboratory (PNL) has developed and tested the highest-transmission neutron-sensing glass fibers reported in the open literature to date. By developing glass compositions specifically for fiber drawing and by using superior oxidationstate controls and rapid quenching, PNL produces, fiber with useful lengths in excess of 200 cm. These long fibers can be used in detectors. Test results on the fibers used as a form-fitting detector around a small storage container containing neutron and gamma ray sources are reported. Excellent neutron-gamma ray discrimination has been achieved. These neutron-sensing glass optical fibers provide for new methods for monitoring the inventory of, preventing the diversion of, and detecting the unauthorized transport of sensitive nuclear materials. As such, it represents a significant potential element in countering the threat of nuclear terrorism.

In the application of micro-structural monitoring, one kind of flexible and stretchable sensing elements was urgently demanded to detect the micro-bending and surface distortions, such as micro-bend sensing elements of medical catheter or smart skin sensing unit of micro-robots. Here the sensing element must be stretchable and flexible for free operation, and must be safe enough when used in bio-medical situation. Although the optical fiber grating is very mature and can be used as sensing element in micro-bending situation, it isn't stretchable enough and flexible enough when used in bio-medical science and micro- structural monitoring, and when applied in human body, the fiber grating isn't safe enough for its easily broken character. In this paper a kind of novel flexible and stretchable polymer grating sensing elements was fabricated by micro-replication process which could be used in micro- structural monitoring, and detailed processes was presented and discussed.

Based on the force analysis, we establish a theoretical model to study the static pressure distribution of the fiber cable spool for the fiber optic guided missile (FOG-M). Simulations indicate that for each fiber layer in the fiber cable spool, the applied static pressure on it asymptotically converges as the number of fiber layers increases. Using the distributed fiber Bragg grating (FBG) sensing technique, the static pressure of fiber cable layers in the spool on the cable winding device was measured. Experiments show that the Bragg wavelength of FBG in every layer varies very quickly at the beginning and then becomes gently as the subsequent fiber cable was twisted onto the spool layer by layer. Theoretical simulations agree qualitatively with experimental results. This technology prov...

Optical-fiber probing is widely employed in bubble/droplet measurement in gas-liquid two-phase flows. Several types of optical fiber probes with a very high S/N ratio and high performance have been developed, but further improvement in the probes' measurement accuracy and reliability for industrial applications is desired. We tried to eliminate optical noise in the probe measurements, and we found that the signals include some peak signs that have potential for advanced measurement with optical-fiber probing. We developed a ray-tracing numerical simulator and identified the mechanisms underlying the generation of the signals. In order to numerically simulate the optical probing signals, the simulator must use 3D frameworks composed of incident beams, the reflection and refraction on the surfaces of the optical elements (i.e., an optical fiber, a sensing tip, an air phase, and a water phase), and beams returning from the sensing tip to the other tip through the fiber. We used all of these in a simple rendering framework based on a ray-tracing algorithm with Fresnel's law, and we observed the mechanism of some promising signals that may be useful for extracting the hidden potential of optical-fiber probing. To verify the simulator's performance, we carried out three comparative experiments with fundamental setups using a wedge-shaped single-tip optical fiber probe, examining: (1) the beam trajectories and energy leaking out from the sensing tip into the surrounding air phase or water phase, (2) the probing signals throughout penetration of the sensing tip at the air-water free interface in light of the three-dimensional deformation, and (3) the probing signals throughout penetration of the sensing tip into a bubble in light of the three-dimensional bubble shape. As a result, (a) we found that an optical fiber probe with a wedge-shaped tip has particular characteristics of beam emissions from the tip, and the emitting angles switched depending on the phases covering the tip. This phenomenon is very effective for further advanced measurement. (b) We observed numerically that the cutting angle of the sensing tip maximizing the air signal level was approximately 30°, and therefore this angle is the best for obtaining the highest S/N ratio. (c) We found that the meniscus shape clearly affected the probing signal optically. (d) We observed the mechanism of a pre-signal caused by the reflection at the frontal and rear interfaces of a bubble. The pre-signal is very useful for practical measurement because it appears only when the probe penetrates the center region of a bubble. We compared the above numerical results with the results of the three experiments, and there was satisfactory correspondence between the numerical and experimental results.

In this paper we present the first incorporation of a microstructured optical fiber (MOF) into biochip applications. A 16-mm-long piece of MOF is incorporated into an optic-fluidic coupler chip, which is fabricated in PMMA polymer using a CO2 laser. The developed chip configuration allows the continuous control of liquid flow through the MOF and simultaneous optical characterization. While integrated in the chip, the MOF is functionalized towards the capture of a specific single-stranded DNA string by immobilizing a sensing layer on the microstructured internal surfaces of the fiber. The sensing layer contains the DNA string complementary to the target DNA sequence and thus operates through the highly selective DNA hybridization process. Optical detection of the captured DNA was carried out using the evanescent-wave-sensing principle. Owing to the small size of the chip, the presented technique allows for analysis of sample volumes down to 300 nL and the fabrication of miniaturized portable devices.

We demonstrate stable wavelength tunable inscription of polymer optical fiber Bragg gratings (FBGs). By straining the fiber during FBG inscription, we linearly tune the center wavelength over 7 nm with less than 1% strain. Above 1% strain, the tuning curve saturates and we show a maximum tuning of 12 nm with 2.25% strain. We use this inscription method to fabricate a dual-FBG strain sensor in a poly (methyl methacrylate) single-mode microstructured polymer optical fiber and demonstrate temperature compensated strain sensing around 850 nm.

As a result of problems such as calibration drift in nuclear plant pressure sensors and the recent oil loss syndrome in some models of Rosemount pressure transmitters, the nuclear industry has become interested in fiber optic pressure sensors. Fiber optic sensing technologies have been considered for the development of advanced instrumentation and control (I&C) systems for the next generation of reactors and in older plants which are retrofitted with new I&C systems. This paper presents the results of a six-month Phase I study to establish the state-of-the-art in fiber optic pressure sensing. This study involved a literature review, contact with experts in the field, an industrial survey, a site visit to a fiber optic sensor manufacturer, and laboratory testing of a fiber optic pressure sensor. The laboratory work involved both static and dynamic performance tests. This initial Phase I study has recently been granted a two-year extension by the U.S. Nuclear Regulatory Commission (NRC). The next phase will evaluate fiber optic pressure sensors in specific nuclear plant applications in addition to other advanced methods for monitoring critical nuclear plant equipment.

In this paper, a new type of smart basalt fiber-reinforced polymer (BFRP) bar is developed and their sensing performance is investigated by using the Brillouin scattering-based distributed fiber optic sensing technique. The industrial manufacturing process is first addressed, followed by an experimental study on the strain, temperature and fundamental mechanical properties of the BFRP bars. The results confirm the superior sensing properties, in particular the measuring accuracy, repeatability and linearity through comparing with bare optical fibers. Results on the mechanical properties show stable elastic modulus and high ultimate strength. Therefore, the smart BFRP bar has potential applications for long-term structural health monitoring (SHM) as embedded sensors as well as strengthening and upgrading structures. Moreover the coefficient of thermal expansion for smart BFRP bars is similar to the value for concrete.

Fiber sensor technologies are overviewed. Since the early 1970s, this field has been developed, on the basis of the same devices and photonic principles as fiber communication technologies. Besides simple configurations, in which the fiber acts only as a data transmission line, sophisticated configurations have also been developed, in which the fiber is used as a device to realize unique sensing mechanisms. The fiber optic gyroscope (FOG) is a good example, and has been developed as an absolute rotation sensor used, for example, for navigation and/or attitude control applications. Compared with traditional spinning-mass gyroscopes, the FOG has advantages, such as a short warming-up time, a light weight, and easy handling. A Japanese satellite, which was launched in August 2005 with a mission to observe the aurora, is controlled with a FOG. The FOG has also been used in consumer applications, such as the camera stabilizer, radio-controlled (RC) helicopter navigation, and the control of humanoid robots. Recently, distributed and multiplexed sensing schemes, in particular, have been studied and developed, in which a long fiber acts like a “nerve” for feeling the strain and/or the temperature distribution along the fiber. Performances of artificial nerve systems have markedly improved within the last couple of years, in spatial resolution and measurement speed. By embedding the “fiber-optic nerve system” in aircraft wings, bridges and tall buildings, these materials and structures can sense damage to prevent disasters.

A novel system for simultaneous operation of multiple fiber optic oxygen sensors (optodes) is described and characterized. The system is based on an array of one hundred several meter long freely positionable polymer optical fibers with an oxygen sensitive luminophore immobilized at the sensing end of each fiber. The opposite ends of the fiber optodes are fixed in a 10x10 matrix and placed in front of a CCD camera and a LED-light source. Oxygen measurements are conducted by simultaneous excitation of all optodes with the LEDs followed by simultaneous lifetime imaging of the one hundred fiber optodes with the camera. Automated digital image analysis allows for calculation of the luminescence lifetime of each fiber optode individually, which can be converted into oxygen partial pressures. Th...

We proposed an optical fiber sensor with simple multimode fiber (MMF)-dispersion compensation fiber (DCF)-multimode fiber structure based on Mach-Zehnder Interferometer (MZI) and researched its temperature and refractive index (RI) sensing characteristics. The sensing principle is based on the interference between core and cladding modes of DCF due to the large core diameter mismatch. Spectral analyses demonstrate that the transmission spectrum is mainly formed by the interference between the dominant excited cladding mode and core modes. The experimental results show that the proposed sensor has high temperature sensitivity of 0.118nm/^oC in the range of 20-250^oC and RI sensitivity of 66.32nm/RIU within the linear sensing range of 1.33-1.39RIU. Therefore, the characteristics of compact s...

Optical fibers are small-in-diameter, light-in-weight, electromagnetic-interference immune, electrically passive, chemically inert, flexible, embeddable into different materials, and distributed-sensing enabling, and can be temperature and radiation tolerant. With appropriate processing and/or packaging, they can be very robust and well suited to demanding environments. In this paper, we review a range of complete end-to-end fiber optic sensor systems that IFOS has developed comprising not only (1) packaged sensors and mechanisms for integration with demanding environments, but (2) ruggedized sensor interrogators, and (3) intelligent decision aid algorithms software systems. We examine the following examples: (1) Fiber Bragg Grating (FBG) optical sensors systems supporting arrays of environmentally conditioned multiplexed FBG point sensors on single or multiple optical fibers: In conjunction with advanced signal processing, decision aid algorithms and reasoners, FBG sensor based structural health monitoring (SHM) systems are expected to play an increasing role in extending the life and reducing costs of new generations of aerospace systems. Further, FBG based structural state sensing systems have the potential to considerably enhance the performance of dynamic structures interacting with their environment (including jet aircraft, unmanned aerial vehicles (UAVs), and medical or extravehicular space robots). (2) Raman based distributed temperature sensing systems: The complete length of optical fiber acts as a very long distributed sensor which may be placed down an oil well or wrapped around a cryogenic tank.

Fiber-optic based smart structures have recently become the subject of intense study in university and industrial research laboratories. A smart structure can monitor itself throughout its lifetime and provide an accurate estimate of its integrity. The sensors in smart structures must therefore be able to detect even small changes in the operating environment (like stress, temperature, chemical reaction, etc.). This paper pertains to the sensing of strain using embedded twisted and braided fibers which have a much greater sensitivity to changes in applied stress than normal fibers as a result of enhanced microbending. In addition, step-index multimode fibers were used in this research program because the ease of manufacture and lower cost of these fibers (compared to the more commonly used graded index fibers) can be significant and deciding factors in many applications. Results obtained from the experimental program confirm the concept and potential of the fibers used in this study for use in smart structures.

We demonstrate a quantitative broadband fiber sensor, based on evanescent field sensing in the cladding holes of an air-suspended solid-core photonic crystal fiber. We discuss the fabrication process, together with the structural- and optical characterization of a range of different fibers. Measured mode profiles are in good agreement with finite element method calculations made without free parameters. The fraction of the light in the hollow cladding can be tuned via the core diameter of the fiber. Dispersion measurements are in excellent agreement with theory and demonstrate tuning of the zero dispersion wavelength via the core diameter. Optimum design parameters for absorption sensors are discussed using a general parameter diagram. From our analysis, we estimate that a sensitivity increase of three orders of magnitude is feasible compared to standard cuvette measurements. Our study applies to both liquid and gas fiber sensors. We demonstrate the applicability of our results to liquid chemical sensing by m...

Optical fibers are employed to sense fingerprint molecular vibrations in ex vivo experiments on the whole brain and detect cell proliferation probes in a model study on a quantitatively controlled solution. A specifically adapted spectral filtering procedure is shown to allow the Raman signal from molecular vibrations of interest to be discriminated against the background from the fiber, allowing a highly sensitive Raman detection of the recently demonstrated EdU (5-ethynyl-2'-deoxyuridine) labels of DNA synthesis in cells.

Thin film coatings of polypyrrole have been extensively used as gas sensors in chemiresistors where the films are deposited on insulating substrates. These polypyrrole films have also been used as coatings to glass optical fiber as a chemo-chromic transducer for gas sensing. For long term mechanical durability of these sensing films, their adhesion to the substrate is very important. Adhesion between polypyrrole films and glass slide substrates is investigated for solution deposited polypyrrole films. The substrate surface is investigated in terms of addition of silane coupling agents and substrate surface roughness, for enhancement of the film substrate adhesion. The adhesion test is performed by the standard ASTM D - 4541 Pull-off Test Method. The films deposited on as-received slides are characterized for their electrical conductivity and optical transmission for their use in both chemiresistor and optical fiber sensor applications for nerve agent DMMP (di-methylmethylphosphonate) sensing.

We present a sensor capable of detecting solution-based nanoparticles using an optical fiber tip functionalized with a photonic crystal cavity. When sensor tips are retracted from a nanoparticle solution after being submerged, we find that a combination of convective fluid forces and optically-induced trapping cause an aggregation of nanoparticles to form directly on cavity surfaces. A simple readout of quantum dot photoluminescence coupled to the optical fiber shows that nanoparticle presence and concentration can be detected through modified cavity properties. Our sensor can detect both gold and iron oxide nanoparticles and can be utilized for molecular sensing applications in biomedicine.

Integrated optical devices offer dense, multifunctional capability in a single robust package but are rarely considered compatible with the fields of remote or distributed sensing or compete in the long-haul with conventional 'one-dimensional' fibers. Here we aim to change that by introducing a 'flat-fiber' process that combines the advantages of of existing low-cost fiber drawing with the functionality of planar lightwave circuits in a novel hybrid format. Adapted from MCVD fiber fabrication, our preforms are deposited and collapsed into a rectangular geometry before drawing, resulting in extended lengths of mechanically flexible flat-fiber material with a photosensitive germanium-doped planar core. Direct UV writing is then used to create arrays of channel waveguides within the core layer, using a 5?m focused laser spot that literally 'draws' refractive index patterns into the flat fiber as it moves. Having recently demonstrated simple building blocks for integrated optical circuits in millimeter-wide flat-fibers (including; channel waveguides, power junctions and splitters, and planar Bragg gratings), our next step is to incorporate structured windows at strategic points along the fiber to allow fluidic access to the evanescent field for local refractive-index-based chemical measurements. By taking this approach, we hope to extend beyond the limitations of traditional planar and fiber substrates, allowing exotic material compositions, device layouts, and local sensing functions to be distributed over extended distances with no coupling or compatibility concerns in highly functional distributed lab-on-a-chip devices.

Distributed fiber optic sensing is a powerful technology used throughout the oil and gas industry. Raman based distributed temperature sensing (DTS) was invented in the early 1980s, and was first utilized in the oil and gas industry in the 1990s. Today, DTS is widely used in conventional oil wells for monitoring water injection, gas lift, well integrity, flow modeling, and thermal asset monitoring. Steam drive oil wells with high temperatures and hydrogen in the well are one of the more challenging applications. Early deployments in hydrogen rich hot wells experienced fiber failures due to increased optical attenuation. This paper reviewed DTS system considerations with the latest Raman technology, hydrogen tolerant optical fibers and fiber deployment. The paper first provided a brief introduction to the technology and discussed DTS sensing based on Raman scattering, including single ended single wavelength DTS system; double ended single wavelength DTS system; and single ended multi wavelength DTS system. Specific deployments that were discussed included pumped fiber deployments and fixed cable deployments. It was concluded that multi-wavelength DTS technology offers state-of-the-art performance with extended service life, accurate data and automatic trace by trace mitigation of dynamic down-hole fiber attenuation. 6 refs., 13 figs.

Over the past five years, Distributed Temperature Sensing (DTS) along fiber optic cables using Raman backscattering has become an important tool in the environmental sciences. Many environmental applications of DTS demand very accurate temperature measurements, with typical RMSE < 0.1 K. The aim of ...

A process is provided for forming a long-lasting, stable, pH-sensitive dye-acrylamide copolymer useful as a pH-sensitive material for use in an optrode or other device sensitive to pH. An optrode may be made by mechanically attaching the copolymer to a sensing device such as an optical fiber.

This book presents the papers given at a conference on electronic equipment. Topics considered at the conference included space communication systems, switching systems, optical fibers, terrestrial radio systems, local area networks, solar cells, solar energy systems, remote sensing, power distribution systems, alternative energy systems, computer networks, digital signal processing, and microelectronic circuits and devices.

technology is explained briefly with focus on harsh environment reliability of the ... for fiber lasers for remote optical communications applications. ... variety of applications including high power, narrow linewidth, remote sensing usage. ... providing stability, narrow line widths, short pulses with high repetition rates to ...

Due to its ability in providing long distance, distributed sensing, the optical fiber sensing technique based on a Brillouin optical time domain reflectometer (BOTDR) has a unique advantage in monitoring the stability and safety of linear structures. This paper describes the application of a BOTDR-based technique to measure the stress within precast piles. The principle behind the BOTDR and the embedding technique for the sensing optical fiber in precast piles is first introduced, and then the analysis method and deformation and stress calculation based on distributed strain data are given. Finally, a methodology for using a BOTDR-based monitoring workflow for in situ monitoring of precast piles, combined with a practical example, is introduced. The methodology requires implantation of optical fibers prior to pile placement. Field experimental results show that the optical fiber implantation method with slotting, embedding, pasting and jointing is feasible, and have accurately measured the axial force, side friction, end-bearing resistance and bearing feature of the precast pile according to the strain measuring data.

In the present study, we report the first fiber optic glucose sensor utilizing localized surface plasmon resonance of metal nanoparticles. The fiber was bent in the form of a U-shaped probe for point detection and sensitivity enhancement. The probe was prepared by first attaching gold nanoparticles on the optical fiber core and then immobilizing glucose oxidase over it. The sensor operates in the intensity modulation scheme in which the absorbance is measured with respect to the changes in the glucose concentration. The presence of glucose in the vicinity of the sensing region changes the refractive index of the film due to the chemical reactions with glucose oxidase. The absorbance of the metal nanoparticle changes significantly due to local refractive index change. The fiber optic U-shap...

We present modeling, design, fabrication and characterization of a new type of all-optical frequency modulated MEMS force sensor based on a mechanically amplified double clamped waveguide beam structure with integrated Bragg grating. The sensor is ideally suited for force measurements in harsh environments and for remote and distributed sensing and has a measured sensitivity of -14 nm/N, which is several times higher than what is obtained in conventional fiber Bragg grating force sensors. © 2011 Optical Society of America.

Various optical spectrum analyzers have been used as strain-sensing equipment in fiber-optic sensing system based on fiber Bragg gratings (FBGs), which has been expected and investigated to monitor the safety of buildings, bridges, road slopes and other structures. An acoustooptic tunable filter (AOTF) with surface acoustic waves (SAWs) on LiNbO3 has been applied to a wavelength monitor as a simple spectrum analyzer in the system, because it has the characteristics of a small size, a simple configuration, fast response, and low cost. It has not been experimentally varified whether the wavelength monitor consisting of an AOTF device can be used as the strain-sensing system. To check the performance, the fabricated wavelength monitor with the AOTF device has been tested in the fiber-optic strain-sensing system using FBGs. As a result, the shift in the Bragg reflection wavelength corresponding to the change in strain at the fiber sensor has been detected for the first time by an AOTF device. The accuracy of the measured wavelength was approximately 0.9 pm at room temperature.   

We discuss present and near-term uses for high-power fiber lasers and amplifiers for NASA- specific applications including planetary topography and atmospheric spectroscopy. Fiber lasers and amplifiers offer numerous advantages for both near-term and future deployment of instruments on exploration and science remote sensing orbiting satellites. Ground-based and airborne systems provide an evolutionary path to space and a means for calibration and verification of space-borne systems. We present experimental progress on both the fiber transmitters and instrument prototypes for ongoing development efforts. These near-infrared instruments are laser sounders and lidars for measuring atmospheric carbon dioxide, oxygen, water vapor and methane and a pseudo-noise (PN) code laser ranging system. The associated fiber transmitters include high-power erbium, ytterbium, neodymium and Raman fiber amplifiers. In addition, we will discuss near-term fiber laser and amplifier requirements and programs for NASA free space optical communications, planetary topography and atmospheric spectroscopy.

This book contains papers presented at the symposium of International Society for Optical Engineering. Topics covered/include: Fiber optic pressure sensor for internal combustion engine; Automotive fiber optic technology: application issues; and Fiber optic guided missile.

We experimentally studied several sensing characteristics of a birefringent microstructured polymer optical fiber. The fiber exhibits a birefringence of the order 2×10-5 at 1.3 ?m because of two small holes adjacent to the core. In this fiber, we measured spectral dependence of phase and group modal birefringence, bending losses, polarimetric sensitivity to strain and temperature. The sensitivity to strain was also examined for intermodal interference observed in the spectral range below 0.8 ?m. Finally, we showed that the material transmission windows shift as function of the applied strain. This shift has an exponential character and saturates for greater strain.

The recent advances of polymer technology allowed the introduction of plastic optical fiber in sensor design. The advantages of optical metrology with plastic optical fiber have attracted the attention of the scientific community, as they allow the development of low-cost or cost competitive systems compared with conventional technologies. In this paper, the current state of the art of plastic optical fiber technology will be reviewed, namely its main characteristics and sensing advantages. Several measurement techniques will be described, with a strong focus on interrogation approaches based on intensity variation in transmission and reflection. The potential applications involving structural health monitoring, medicine, environment and the biological and chemical area are also presented. PMID:20459238

Luminescence has become an invaluable analytical tool for development of robust fiber optical sensors for many industrial, biomedical and environmental applications. Direct intensity measurements of the luminescent emission are, due to their simplicity, a very common measuring principle. Consequently, many optical fiber sensors are based on the intensity measurement of the luminescence emission. Unfortunately, direct luminescent intensity measurements suffer from a series of analyte-independent fluctuations, which make them inappropriate for the development of reliable instrumentation for chemical sensing applications. A possibility for solving this trouble is to measure the lifetime of the luminescence emission. The drawbacks of such approach are an increase in the complexity of the syste...

The design and fabrication of a fiber optic pH sensor working on the basis of evanescent wave absorption is presented. A pH sensitive dye is immobilized on the uncladded portion of the optic fiber by sol-gel route. The sensitivity of the device is found to increase when multiple sol-gel coatings are used as the cladding in the sensing region. The sensor response and its dynamic range are reported for two pH indicator dyes, vis. bromocresol purple and bromocresol green.

This paper describes a new optical sensing device for on-line monitoring of the temperature, velocity and trajectory of in-flight particles during industrial coating production. Thermal radiation emitted by the in-flight particles is collected by a small and robust sensing head that can be attached to the plasma gun providing continuous monitoring of the spray process. The collected radiation is transmitted through optical fibers to a detection cabinet located away from the dusty environment around the operating plasma gun. On-line measurement of the particle velocity, temperature and trajectory can provide an efficient diagnostic tool to maintain optimum spraying conditions leading to a better reproducibility of the coating properties.

A novel tunable fiber ring laser configuration with a combination of bidirectional Raman amplification and dual erbium-doped fiber (EDF) amplification is proposed for realizing high optical signal-to-noise ratio (SNR), long-distance, quasi-distributed fiber Bragg grating (FBG) sensing systems with large capacities and low cost. The hybrid Raman-EDF amplification configuration arranged in the ring laser can enhance the optical SNR of FBG sensor signals significantly owing to the good combination of the high gain of the erbium-doped fiber amplifier (EDFA) and the low noise of the Raman amplification. Such a sensing system can support a large number of FBG sensors because of the use of a tunable fiber Fabry-Perot filter located within the ring laser and spatial division multiplexing for expansion of sensor channels. Experimental results show that an excellent optical SNR of approximately 60 dB has been achieved for a 50 km transmission distance with a low Raman pump power of approximately 170 mW at a wavelength of 1455 nm and a low EDFA pump power of approximately 40 mW at a wavelength of 980 nm, which is the highest optical SNR achieved so far for a 50 km long FBG sensor system, to our knowledge. PMID:16936857

A novel optical load cell based on Fiber Bragg Grating sensing technique was proposed for icing monitoring on high-voltage overhead transmission lines. Compared to the conventional strain gauge load cell, the developed optical load cell has several unique advantages such as unnecessary power supply on site, excellent ability for avoiding electromagnetic interference, and long lifespan. In the load cell design, coupled dual-beam ('S' beam) structure was adopted to achieve an accurate measurement, and the part of FBG bonding was carefully chosen to withstand equal and opposite strain, which solved the problem of cross-sensitivity between strain and temperature of FBG sensing. A mixed WDM/TDM (Wave-Division Multiplexing/Time-Division Multiplexing) optical fiber network is proposed to construc...

On-fiber optical sensors, designed with chromogenic materials used as the fiber modified cladding, were developed for sensing environmental conditions. The design was based on the previously developed on-fiber devices. It is known that the light propagation characteristics in optical fibers are strongly influenced by the refractive index of the cladding materials. Thus, the idea of the on- fiber devices is based on replacing the passive optical fiber cladding with active or sensitive materials. For example, temperature sensors can be developed by replacing the fiber clad material with thermochromic materials. In this paper, segmented polyurethane-diacetylene copolymer (SPU), was selected as the thermochromic material for temperature sensors applications. This material has unique chromogenic properties as well as the required mechanical behaviors. During UV exposure and heat treatment, the color of the SPU copolymer varies with its refractive index. The boundary condition between core and cladding changes due to the change of the refractive index of the modified cladding material. The method used for the sensor development presented involves three steps: (a) removing the fiber jacket and cladding from a small region, (b) coating the chromogenic materials onto the modified region, and (c) integrating the optical fiber sensor components. The experimental set-up was established to detect the changes of the output signal based on the temperature variations. For the sensor evaluation, real-time measurements were performed under different heating-cooling cycles. Abrupt irreversible changes of the sensor output power were detected during the first heating-cooling cycle. At the same time, color changes of the SPU copolymer were observed in the modified region of the optical fiber. For the next heating-cooling cycles, however, the observed changes were almost completely reversible. This result demonstrates that a low-temperature sensor can be built by utilizing the chromogenic SPU copolymer as the modified cladding material.

A Raman probe has been developed utilizing a single optical fiber as both a light pipe and an active sensing element. By coating a small segment of the surface of an exposed glass fiber core with a thin polymer film, an inverted waveguide is formed where light transmitted down the fiber is stripped out of the core and into the polymer film. The polymer coating is used both as a waveguide and as a medium for concentrating small organic molecules to be interrogated by Raman spectroscopy. The ability of the fiber optic thin film waveguide probe to detect organic vapors is demonstrated. The utility of the probe in the detection of nonaqueous phase liquids (NAPLs) is also described.

Insulation failures caused by partial discharges (PD) in power transformers affect safety and financial terms in power systems. The method to measure acoustic pressure generated by PD is researched widely. An all-fiber sensor that is dielectric structure is potential demand in high voltage power equipment. In this paper, an optical fiber system based on Fabry-Perot (FP) sensor is established to detect ultrasonic signals generated by PD in transformer oil. As a sensing unit of the sensor, Fabry-Perot cavity is formed between a quartz diaphragm sensitive to dynamic signal and an end of fiber pigtail. The output optical signal is modulated by acoustic signal reacted on the diaphragm. A new demodulation method to FP sensor using Fiber Bragg Gating is presented. The system has inherent immunity to electromagnetic interference and resistance to harsh environment. According to theoretic analysis and computer simulation, the system shows high sensitivity and resolution.

Phase distortion happens in the distributed optical fiber oil and gas pipeline leak detection and early warning system, which results in decreased sensitivity of the system and bigger location errors. This paper studies the birefringent characteristic of the optical fiber interferometer sensing arm, and the Jones matrix model of the optical polarization is established. On the basis of this model the optical path and location principle are improved by using two 3x3 couplers to acquire four light signals. Then, the demodulation method is adopted to get phase differences induced by perturbation of the two reverse optical paths, which are used subsequently in cross-correlation algorithm to achieve the time-delay estimation. Compared to the method of polarization control, this approach simplifi...

An innovative technique for fabricating the optical fiber hybrid wavelength-division multiplexing (WDM) coupler is presented. The device is comprised of two components, a wavelength division multiplexer and an optical fiber coupler, in a miniature stainless steel tube. The outstanding features of the ultra-low polarization dependent loss (PDL) under 0.05 dB and the compact size of \\emptyv 3.5 × 65 mm for bare-fiber type of package are accomplished by using the pioneering methodology combining the main techniques of twisted and parallel fusion processes in the fused biconical taper (FBT) technology. Besides, its miniaturization is more competitive in both of the applications of optical communication and sensing systems where a compact-sized package is required for extending the flexibility of installation.

A simplified and accurate system of Brillouin optical correlation domain analysis for fiber-optic distributed strain sensing is proposed and demonstrated. In the system, pump and probe lightwaves, with about 11 GHz frequency difference for stimulating fiber Brillouin scattering, are generated accurately in a time-division way by using direct-frequency-modulation nature of a laser diode. We have developed a scheme for rigorously compensating frequency modulation response of the laser diode to realize accurately a rectangular frequency modulation with such large amplitude for the time-division pump-prove generation. Distribution of Brillouin gain spectrum along an optical fiber has successfully been measured, with 16 cm spatial resolution, using the waveform pre-compensated accurately for the laser frequency modulation.   

Abstract A polarization-independent optical sensor is created by fabricating a concentric gold ring grating with a period of 900 nm on the end facet of an optical fiber. The sensing function of this miniaturized device is realized by sending white light as a probe to the gold rings and collecting the response signal in the back-reflection through the optical fiber. A pronounced peak due to the Rayleigh anomaly of the gold ring grating is observed in the reflection spectrum, the center wavelength of which is sensitive to the change in the environmental refractive index of the fiber end facet. Theoretical analysis not only shows excellent agreement with the experimental results, but also gives insights into the mechanisms of this kind of sensor. Using the center position of the Rayleigh peak...

In this work, we report a sensing configuration of the fiber taper intrinsic Fabry-Perot interferometer directly inscribed in single-mode optical fiber tapers with different waist diameters from 14 to 80 ?m using a femtosecond laser micromachining system. By controlling the inscribing depth and intensity of the fs laser pulse, the fringe visibility can exceed 9.0 dB when the fiber taper waist diameter is around 15 ?m, which is sufficient for most sensing applications. The sensor sensitivity depends on the fiber taper waist diameter, while a smaller diameter corresponds to a large sensitivity. Different free spectral ranges can be achieved for various cavity lengths. Such a structure can combine the high sensitivity properties of fiber taper sensors with the high resolution features of Fabry-Perot interferometer sensors. Meanwhile, this structure can have a number of outstanding advantages, such as its small size, unique geometry, easy fabrication, low cost and capability for mass production. These fiber taper intrinsic Fabry-Perot interferometer sensors have high potential in fast detection and high precision measurement while maintaining superior reliability for chemical and biological sensing.

The use of an optical fiber as a distributed sensor for detecting and locating intruders over long perimeters (>10 km) is described. Phase changes resulting from either the pressure of the intruder on the ground immediately above the buried fiber or from seismic disturbances in the vicinity are sensed by a phase-sensitive optical time-domain reflectometer (?-OTDR). Light pulses from a cw laser operating in a single longitudinal mode and with low (MHz/min range) frequency drift are injected into one end of the single mode fiber, and the backscattered light is monitored with a photodetector. In laboratory tests with 12 km of fiber on reels, the effects of localized phase perturbations induced by a piezoelectric fiber stretcher on ?-OTDR traces were characterized. In field tests in which the sensing element is a single mode fiber in a 3-mm diameter cable buried in a 20-46 cm deep, 10 cm wide trench in clay soil, detection of intruders on foot up to 4.6 m from the cable line was achieved. In desert terrain field tests in which the sensing fiber is in a 4.5-mm diameter cable buried in a 30 cm deep, 75 cm wide trench filled with loose sand, high sensitivity and consistent detection of intruders on foot and of vehicles traveling down a road near the cable line was realized over a cable length of 8.5 km and a total fiber path of 19 km. Based on these results, this technology may be regarded as a candidate for providing low-cost perimeter security for nuclear power plants, electrical power distribution centers, storage facilities for fuel and volatile chemicals, communication hubs, airports, government offices, military bases, embassies, and national borders.

We present an approach towards design and fabrication of optical microsystems based on UV-replication techniques using Ormocer materials. An integration of the structures on chip level is demonstrated for Vertical Surface Emitting Lasers (VCSEL). VCSEL's are of increasing interest for various fields such as telecommunications, optical sensing and optical interconnects. In terms of optical system integration, high technological requirements are imposed. UV-replication techniques using Ormocer materials offer a cost-effective way of integrating micro-optical elements directly on the chip with reduced assembly effort. Structures up to several hundred microns thickness and alignment tolerances in the order of few microns can be produced. The method is suitable for the fabrication of single elements, arrays and is extendable to wafer-scale processing. Here, we give an example for the coupling of VCSEL arrays into multimode optical fibers using two different approaches: Focusing of the VCSEL output into the fiber using replicated microlenses and fiber butt-coupling of the VCSEL lasers with help of replicated fiber alignment/guiding structures. Origination of the structure elements is accomplished by direct laser writing into photoresist and resist reflow techniques, respectively. Specific limitations of the corresponding fabrication method are already taken into account during element design and modeling. Results for the replicated lenses show a total fiber launch efficiency better than 70% over the laser operational range with alignment tolerances of approximately +/- 10 micrometers , which can be met by passive fiber alignment. In case of the replicated fiber alignment/guiding structures, fiber launch efficiencies better than 50% over the operation range and peak values better than 80% are reported.

The ability to detect hydrogen gas leaks economically and with inherent safety is an important technology that could facilitate commercial acceptance of hydrogen fuel in various applications. In particular, hydrogen fueled passenger vehicles will require hydrogen leak detectors to signal the activation of safety devices such as shutoff valves, ventilating fans, alarms, etc. Such detectors may be required in several locations within a vehicle--wherever a leak could pose a safety hazard. It is therefore important that the detectors be very economical. This paper reports progress on the development of low-cost fiber-optic hydrogen detectors intended to meet the needs of a hydrogen-fueled passenger vehicle. In the design, the presence of hydrogen in air is sensed by a thin-film coating at the end of a polymer optical fiber. When the coating reacts reversibly with the hydrogen, its optical properties are changed. Light from a central electro-optic control unit is projected down the optical fiber where it is reflected from the sensor coating back to central optical detectors. A change in the reflected intensity indicates the presence of hydrogen. The fiber-optic detector offers inherent safety by removing all electrical power from the leak sites and offers reduced signal processing problems by minimizing electromagnetic interference. Critical detector performance requirements include high selectivity, response speed and durability as well as potential for low-cost production.

This dissertation reports the development of two new categories of optical fibers. These are the Random Hole Optical Fiber (RHOF) and the Crucible Technique Hybrid Fiber (CTF). The RHOF is a new class of microstructure fiber which possesses air holes which vary in diameter and location along the length of the fiber. Unlike all prior microstructure fibers, these RHOF do not have continuous air holes which extend throughout the fiber. The CTF is a method for incorporating glasses with vastly differing thermal properties into a single optical fiber. Each of these two classes of fiber brings a new set of optical characteristics into being. The RHOF exhibit many of the same guidance properties as the previously researched microstructure fibers, such as reduced mode counts in a large area core. CTF fibers show great promise for integrating core materials with extremely high levels of nonlinearity or gain. The initial goal of this work was to combine the two techniques to form a fiber with exceedingly high efficiency of nonlinear interactions. Numerous methods have been endeavored in the attempt to achieve the fabrication of the RHOF. Some of the methods include the use of sol-gel glass, microbubbles, various silica powders, and silica powders with the incorporation of gas producing agents. Through careful balancing of the competing forces of surface tension and internal pressure it has been possible to produce an optical fiber which guides light successfully. The optical loss of these fibers depends strongly on the geometrical arrangement of the air holes. Fibers with a higher number of smaller holes possess a markedly lower attenuation. RHOF also possess, to at least some degree the reduced mode number which has been extensively reported in the past for ordered hole fibers. Remarkably, the RHOF are also inherently pressure sensitive. When force is applied to an RHOF either isotropically, or on an axis perpendicular to the length of the fiber, a wavelength dependent loss is observed. This loss does not come with a corresponding response to temperature, rendering the RHOF highly anomalous in the area of fiber optic sensing techniques. Furthermore an ordered hole fiber was also tested to determine that this was not merely a hitherto undisclosed property of all microstructure fibers. Crucible technique fibers have also been fabricated by constructing an extremely thick walled silica tube, which is sealed at the bottom. A piece of the glass that is desired for the core (such as Lead Indium Phosphate) is inserted into the hole which is in the center of the tube. The preform is then drawn on an fiber draw tower, resulting in a fiber with a core consisting of a material which has a coefficient of thermal expansion (CTE) or a melting temperature (Tm) which is not commonly compatible with those of silica.

For the past decade NASA programs have utilized the Diamond AVIM connector for optical fiber assemblies on space flight instrumentation. These connectors have been used in communications, sensing and LIDAR systems where repeatability and high performance are required. Recently Diamond has released a smaller form factor optical fiber connector called the "Mini-AVIM" which although more compact still includes the tight tolerances and the ratcheting feature of the heritage AVIM. NASA Goddard Space Flight Center Photonics Group in the Parts, Packaging and Assembly Technologies Office has been performing evaluations of this connector to determine how it compares to the performance of the AVIM connector and to assess its feasibility for harsh environmental applications. Vibration and thermal testing were performed on the Mini-AVIM with both multi-mode and single-mode optical fiber using insitu optical transmission monitoring. Random vibration testing was performed using typical launch condition profiles for most NASA missions but extended to 35 Grms, which is much higher than most requirements. Thermal testing was performed incrementally up to a range of -55°C to +125°C. The test results include both unjacketed fiber and cabled assembly evaluations. The data presented here indicate that the Mini-AVIM provides a viable option for small form factor applications that require a high performance optical fiber connector.

We report that electropolymerization parameters (duration and voltage) modulate the properties and morphological structures of photoactive polymers which influence both the efficiency of bioreceptor attachment to the polymer surface, and the resulting biosensor assay performance. We have compared two biosensor technologies, optical and electrochemical, for the detection of anti-cholera toxin antibodies using our singular conductive optic fibers, albeit at this stage in separate experiments. Both biosensor systems were more sensitive than conventional detection and pave the way for the possibility to one day make simultaneous optical and electrochemical sensing using the same biosensor. (author)

A highly sensitive low cost fiber-optic humidity sensor based on evanescent wave scattering and evanescent wave absorption has been developed. The sensor is fabricated using a U-bend optical fiber which is coated with silica film using sol-gel process and doped with Methylene Blue. We investigated the sensing property of the sensor in different aspects and found that the normalized absorbance of the sensor at wavelength 540nm is logarithmic linear with the relative humidity (RH%) in the range between 1.1% and 70% at room temperature (291K). In RH between 1.1% and 4.1%, the sensor shows good linear relationship with a sensitivity of 0.0087a.u.%^-^1 (0.087dB%^-^1) and limit of detection (LOD) of 0.062%. We also found that the sensitivity rely more on the length of sensing region than the ben...

The water infiltration in soils is very useful information in improving irrigation methods and systems in order to maximize the efficiency of water use. Heat pulse sensors have been proposed as useful tools for measuring soil water fluxes, but have the limitation of measuring in a small portion of the soil (point measurements). Several studies have demonstrated the validity of Distributed Temperature Sensing (DTS) fiber optic applications to measure water flux in porous media, whether passively or actively heating the fiber optic cable and studying its performance. Using this technique, the Active Heat Pulse Method with Fiber Optic temperature sensing (AHFO), water infiltration through the soil can be estimated simultaneously at many points within 0.125 m intervals and along large distances with high temporal frequency. In order to estimate the infiltration rate and its variability in an agricultural field with sandy-loam soil, a fiber optic cable was installed in the field at two depths, 0.30 m and 0.60 m, and in 39.5 m long parallel transects. Two ring infiltrometers of 1 m diameter, spaced 0.5 m, were placed above the fiber transects to measure the infiltration and they were filled with water to a height of 0.10 m. Simultaneously, the fiber optic cable was heated by applying a power of 20 W/m to its metallic protective jacket. Temperature was recorded in the DTS unit every 2 s and its evolution over time was studied to determine the infiltration rate. First, readings were taken in one infiltrometer, then they were taken with the other while the first was moved forward to the next location. This procedure was replicated along the transects at our defined measurement points. The results show that the AHFO is a useful tool for studying infiltration, its evolution and its variability in the field. This could be of interest in many agricultural and environmental studies, such as designing, evaluating, and managing irrigation units.

We show the performance enhancement of a distributed temperature sensing system based on Raman scattering in optical fibers by using correlation codes. Specifically, we demonstrate experimentally that the use of Golay sequences provide an improvement in the signal to noise ratio by a factor of 10 dB, thereby providing an improvement in the temperature uncertainty by a factor of 2.5 over conventional technique.

We describe laboratory experiments with a fiber-optic sensor employing a chirped laser that detects, with 20-30 micrometer accuracy, displacements of a remote reflective target at distance of 200-500 mm. The requirements of chirp linearity and laser coherence in order to achieve this sensitivity are elaborated. This sensor can be employed for remotely sensing minute displacements of objects in harsh environments, including cryo-magnets in particle accelerators.

In this study, we have fabricated a fiber-optic pH sensor, which is composed of a light source, a pH-sensing probe, plastic optical fibers and a spectrometer, for determining the degree of infection by Helicobacter pylori in the stomach. As pH indicators, phenol red and m-cresol purple are used, and pH liquid solutions are prepared by mixing phenol red or m-cresol purple solutions and various kinds of pH buffer solutions. The light emitted by a light source is guided by plastic optical fibers to the pH liquid solution, and the optical characteristic of a reflected light is changed according to the color variations of the pH indicator in the pH-sensing probe. Therefore, we have measured the intensities and wavelength shifts of the reflected lights, which change according to the color variations of indicators at different pH values, by using a spectrometer for spectral analysis. Also, the relationships between the pH values of liquid solutions and the optical properties of the modulated lights are obtained on the basis of the changes of the colors of indicators.

This Letter reports a polymer optical fiber (POF) based large strain sensor based on the multimode interference (MMI) theory for the application of structural health monitoring. A section of POFs is sandwiched between two silica single mode fibers to construct a single-mode-multimode-single-mode structure that produces a MMI spectrum. The strain sensing mechanism of the device was investigated and experimentally verified. A large dynamic range of 2×104???? (2%) and a detection limit of 33 µ? have been demonstrated. PMID:23073446

The main objective of the present work is to develop an optical fiber relative humidity (RH) sensor having a linear response throughout over the widest possible dynamic range. We report an optical fiber RH sensor based on the evanescent wave absorption spectroscopy that fulfills this objective. The fiber sensor employs a specific nanoparticle (zinc oxide) doped sol-gel nanostructured sensing film of optimum thickness, synthesized over a short length of a centrally decladded straight and uniform optical fiber. A detailed experimental investigation is carried out to analyze the sensor response/characteristics. Fiber sensor response is observed to be linear throughout the dynamic range as wide as 4% to 96% RH. The observed linear sensitivity for the fiber sensor is 0.0012?RH(-1). The average response time of the reported sensor is observed to be as short as 0.06?s during the humidification. In addition, the sensor exhibited a very good degree of reversibility and extremely high reliability as well as repeatability. PMID:21947051

High-birefringent polarization-maintaining fibers are studied theoretically and experimentally. First of all, simple formulas of birefringence and modal dispersion are obtained for high-birefringent elliptical fibers by variational method with a Gaussian approximation. The birefringence, dispersion and electric field distributions of single- and double-clad elliptical fibers are discussed in detail. Based on an analysis of the elliptical fiber, strain and temperature sensitivities without built-in stresses are calculated. A design to minimize the temperature or strain sensitivities by suitably selecting the fiber parameters, such as core ellipticity, refractive index difference and thickness of the inner cladding is presented. A double -clad elliptical fiber is more flexible for this design. A novel method for minimizing the temperature sensitivity of PM fiber with high strain sensitivity is proposed using a double-clad elliptical fiber with stress applying inner elliptical cladding. This is achieved by suitably selecting doping materials for the core and the inner cladding to balance the built-in stresses in the core and cladding of the fibers. The temperature and strain sensitivities and the design of temperature-insensitive fibers with high strain sensitivities are discussed. Such fibers are suitable for polarimetric strain sensors. An example of the fiber design is given and the strain sensitivity of 50 rad/mm is obtained with zero temperature sensitivity. A dynamic polarimetric fiber-optic measuring system is built. The strain and temperature sensitivities of three common types of high-birefringent PM fibers: bow -tie, PANDA and elliptical core fibers are measured. The measurement process is automatic and controlled by a microprocessor or PC. The results match well with other publications. Polarization properties of high-birefringent elliptical fibers under bending and lateral pressure are studied using coupled-mode theory. Bending and pressure effects are treated as perturbations to refractive index by photoelastic theory. Numerical results are given in terms of various fiber parameters, the normalized frequency, the ratio of the major axis to the minor axis of the core, the ratio of the inner cladding major axis to the core major axis, and the difference between the core index and the inner cladding index. For the special case of a circular single -mode fiber, the results agree with the existing publications. Finally, some potential applications of temperature -insensitive PM fibers in polarimetric sensing systems are discussed. Smart structures and skins, electric and magnetic field sensors, current, acoustic, displacement, acceleration and flow rate sensors are among the possibilities. Moreover, a future research for two-mode highly elliptical fibers is suggested.

We present modeling and design of an all-optical MEMS Bragg grating (half-pitch of 125 nm) strain sensor for single-fiber distributed sensing. Low optical loss and the use of frequency modulation rather than amplitude modulation, makes this sensor better suited for distributed systems than comparable designs, e.g. Fabry-Perot and Mach-Zender. Also, multiplexing of several sensors with different period gratings, allow sensors to be connected to a single fiber, thereby minimizing cabling and simplifying readout. We show through analytical analysis and finite element modeling (FEM) that large mechanical amplification can be obtained if using an angled double beam micrometer scale MEMS structure, compared to conventional fiber Bragg grating sensors. An optimized design and fabrication process is presented.

Fiber Bragg grating (FBG) is a mature sensing technology for the measurement of strain, vibration, acoustics, acceleration, pressure, temperature, moisture, and corrosion. It has gained rapid acceptance in civil, aerospace, chemical and petrochemical, medicine, aviation and automotive industries. The most prominent advantages of FBG are: small size and light weight, distributed array of FBG transducers on a single fiber, and immunity to radio frequency interference. However, a major disadvantage of FBG technology is that conventional state-of-the-art FBG interrogation system is typically bulky, heavy, and costly bench top instruments that are typically assembled from off-the-shelf fiber optic and optical components integrated with a signal electronics board into an instrument console. Base...

A resonator fiber optic gyro is a high accuracy inertial rotation sensor based on the Sagnac effect. Fiber ring resonator is the core-sensing element in the resonator fiber optic gyro. The dynamic response of the resonator has been studied, and the ringing phenomenon is observed when sweeping the laser frequency. The dynamic characteristics of the resonator, which are related with the frequency sweep rate, have a decisive effect on the dynamic performance of the gyro system. In order to further analyze and better design the gyro system, deep analysis of the dynamic resonance characteristics is in urgent need. This paper gives out the condition for the ringing phenomenon, and analyzes the parameters for the ringing and the dynamic resonance curve through simulation. It is concluded that inc...

We report a novel all-fiber narrow-bandwidth intermodal Mach–Zehnder interferometer (MZI) based on a long-period fiber grating (LPFG) combined with a fiber bitaper, and the MZI has no special limit for the resonant wavelength of the LPFG. Its responses to temperature and axial strain are studied theoretically and experimentally. Experimental results indicate that the temperature sensitivity is 0.0585nm/°C within the temperature range from 30°C to 90°C and the axial strain sensitivity of 0.00013nm/?? can be neglected. Furthermore, as only the common single-mode fiber (SMF) is required during the fabrication process, the proposed device is cost effective and has good practicability in the optical sensing systems.

Fiber optic sensors based on polymer optical fibers (POF) have the advantage of being very elastic and robust at the same time. Unlike silica fibers, standard PMMA POF fibers can be strained to more than 40% while fully maintaining their light guiding properties. We investigated POF as a distributed strain sensor by analysing the backscatter increase at the strained section using the optical time domain reflectometry (OTDR) technique. This sensing ability together with its high robustness and break-down strain makes POF well-suited for integration into technical textiles for structural health monitoring purposes. Within the European research project POLYTECT (Polyfunctional textiles against natural hazards) technical textiles with integrated POF sensors, among others sensors are being developed for online structural health monitoring of geotechnical structures. Mechanical deformation in slopes, dams, dikes, embankments and retrofitted masonry structures is to be detected before critical damage occurs. In this paper we present the POF strain sensor properties, reactions to disturbing influences as temperature and bends as well as the results of the different model tests we conducted within POLYTECT. We further show the potential of perfluorinated graded-index POF for distributed strain sensing with increased spatial resolution and measurement lengths.

stage gun. It was necessary to use optical methods because electrical shorting pins damaged the projectile:, turned .the projectile causing tilted impacts, and sprayed the target with bits of broken pin. The first optical method involved cutting shrzllow grooves in the sides of the projectile at precisely measured intervals. Thc projectile pilssed through a single light beam focused in such a way that the grooves would alternately block and transmit light to a sensing system. This system didn't work because the groovas filled with smoke, blocking the light at all times after the projectile first broke the hearn. The second method used light rcflectetl off the projectile at four different positions. Light from a 400 mW laser was split into four oplical fibers. Half of the light reflected from the end of each B9er 'was retutncd to it phototnulitiplier. When the projectile passed in front of a fiber the amount of returned light increased. This system had a very poor signal to noise ratio: the amount of light returned when the projectile passed in front ofthe fiber was scarcely larger than the noise on the signals. 'I'hc third system used four stations at which laser light was transmitted from one optical fiber to another. 'The projectile passed close by tlhe sending or receiving fiber, rapidly cutting off the transmitted light. This method suffered from a lasix speckle pattern which changed with time thereby giving a constiintly changing inlerisiily. The fiber optic beam splitter used to split the laser light in methods two and three was also very nnstable: the amount of light split into any particular fiber varied with teinperature, vibration, and any movement of fibers. The method which was ultimately successful used it SmW, 670 nni laser diode at each of' four positions. A small lens focused this light to a point through which Ilie projectile passed. Transmitted light was imaged into 700 micron plastic fibers which relayed thhe light to a bank of photomultipliers. 'The combination of imaging the luminous area of the laser diodc and the end of the sensing fiber onto the same plane, through which the projectile passed, piovided veiy good rejection of stray light, a very fast light cutoff as the projectile passed tlwough the focal point, and efficient use of light. Projectile velocities were measured with an accuracy of 1 part in 1,000. In addition to our optical projectile velocity measuring system, we have significantly changed our projectiles, OUI transition section diaphragms, and developed a new honing teditiique. Thesc will be briefly discuswd as well.

of carbon fiber cost and also to the sensing performance of carbon fiber reinforced concrete based structures. For carbon fiber concrete electrical resistance increases with tensile stress and decreases upon compression....

The present invention relates generally to secure fiber optic communications and more particularly to an apparatus which effects the efficient coupling of light from multiple optic fibers into a single optic fiber. This invention is comprises of an apparatus for simultaneous transmission of optic signals having different wavelengths over a single optic fiber. Multiple light signals are transmitted through optic fibers that are formed into a circumference surrounding a central core fiber. The multiple light signals are directed by a lens into a single receiving fiber where the light combines and is then focused into the central core fiber which transmits the light to a wavelength discriminating receiver assembly. 2 figs.

In the paper we present the results of our research on optical fiber sensors embedded into composite material samples. We investigate the influence of the lamination process, axial orientation of an optical fiber sensor and coating of a fiber on stress monitoring of a composite material. In the paper we present two approaches to the case of composite condition monitoring, using a polarimetric fiber optic sensor as well as fiber Bragg gratings. We also present experimental evidence that interaction between a composite material and fiber optic sensors is very significant and depends on many factors such as fiber optic axial orientation and the coating layer surrounding an optical fiber.

level. Technology transfer to the SIM flight team is now well along. Keywords: optical ..... Gates constitutes demonstration that a NASA Technology Readiness Level .... Optical Bench; Fiber Splitters; Fiber Switches; Fiber Distribution Assembly; ...

Smart structures which contain dense two- or three-dimensional arrays of attached or embedded sensor elements inherently require signal multiplexing and processing capabilities to permit good spatial data resolution as well as the adequately short calculation times demanded by real time active feedback actuator drive circuitry. This paper reports the implementation of an in-line optical signal processor and its application in a structural sensing system which incorporates multiple discrete optical fiber sensor elements. The signal processor consists of an array of optical fiber couplers having tailored s-parameters and arranged to allow gray code amplitude scaling of sensor inputs. The use of this signal processor in systems designed to indicate the location of distributed strain and damage in composite materials, as well as to quantitatively characterize that damage, is described. Extension of similar signal processing methods to more complicated smart materials and structures applications are discussed.

Papers are presented on quantum optics and electronics, VUV and X-ray lasers, excimer lasers, free electron lasers, chemical lasers, nuclear-pumped lasers, directed energy technology for strategic defense, discharge lasers, and high power gas lasers. Also covered are CO2 and FIR lasers, ultrafast lasers and techniques, dye lasers, solid state lasers, semiconductor and diode lasers, and nonlinear effects in fibers and fiber lasers. Additional papers are also presented on dynamic gratings and wave mixing; laser radars, lidars, and remote sensing; diode laser applications; adaptive optics and propagation; ultrafast phenomena; laser spectroscopy and lasers in chemistry; laser dyes; and imaging techniques. Finally, papers covering optical devices and measuring instruments, lasers in medicine, lasers in industry, and lasers in education round out the proceedings.

An optimized, compact Raman system for field environmental analysis is being developed. The Raman system uses diode laser excitation, fiber-optic probes, a new generations of imaging spectrometers, and solid state detectors. Emphasis has centered on optimizing the Raman apparatus, determining the best fiber optic probe technology that will allow remote sensing (i.e. down a well or simultaneous multipoint monitoring), establishing quality control procedures, and developing camera control and data analysis software. Sensitivities for a variety of compounds will be presented demonstrating major reductions in detection limits. New approaches for implementing very high throughput monochromators will be discussed, and their impact on the overall Raman system considered. The latest generation of solid state detectors including Charged-Coupled Devices (CCD) and Charge-Injection Devices (CID) will be reviewed. Over the last several years, these detectors have contributed to major advances in Raman spectroscopy. An overview of combining proper optical systems with currently available and soon to be introduced detectors will be presented.

In this paper, a novel kind of method to monitor corrosion expansion of steel rebars in steel reinforced concrete structures named fiber optic coil winding method is proposed, discussed and tested. It is based on the fiber optical Brillouin sensing technique. Firstly, a strain calibration experiment is designed and conducted to obtain the strain coefficient of single mode fiber optics. Results have shown that there is a good linear relationship between Brillouin frequency and applied strain. Then, three kinds of novel fiber optical Brillouin corrosion expansion sensors with different fiber optic coil winding packaging schemes are designed. Sensors were embedded into concrete specimens to monitor expansion strain caused by steel rebar corrosion, and their performance was studied in a designed electrochemical corrosion acceleration experiment. Experimental results have shown that expansion strain along the fiber optic coil winding area can be detected and measured by the three kinds of sensors with different measurement range during development the corrosion. With the assumption of uniform corrosion, diameters of corrosion steel rebars were obtained using calculated average strains. A maximum expansion strain of 6,738 ?? was monitored. Furthermore, the uniform corrosion analysis model was established and the evaluation formula to evaluate mass loss rate of steel rebar under a given corrosion rust expansion rate was derived. The research has shown that three kinds of Brillouin sensors can be used to monitor the steel rebar corrosion expansion of reinforced concrete structures with good sensitivity, accuracy and monitoring range, and can be applied to monitor different levels of corrosion. By means of this kind of monitoring technique, quantitative corrosion expansion monitoring can be carried out, with the virtues of long durability, real-time monitoring and quasi-distribution monitoring. PMID:22346672

This letter proposes novel optical fiber cables with extremely small cable diameter that employs rollable 20-fiber ribbons, which will improve fiber ribbon and cable productivity compared with optical fiber cable employing rollable 4-fiber ribbons. We fabricated the cables and investigated its feasibility in terms of high-count compactness, cable productivity, fiber strain induced by cable bending, optical loss characteristics and capacity for mass splicing. As a result, we confirmed the excellence of these cables and their fiber splicing workability.   

The ability to operate despite failure will become increasingly important as the use of optical sensor networks grows, and the amount of sensing information to be handled by a sensor network is increasing, especially for safety and security applications. In this review, the four categories of protection to allow service to be reestablished after a failure (dedicated/shared and line/path) are thoroughly discussed. This paper also presents an overview of the most representative robust fiber-optic sensor systems, discussing their schemes, pros and cons.

An optical fiber humidity sensor employing an in-house scaled TiO2-nanoparticle doped nanostructured thin film as the fiber sensing cladding and evanescent wave absorption is reported. The main objective of the present work is to achieve a throughout-linear sensor response with high sensitivity, possibly over a wide dynamic range using the simplest possible sensor geometry. In order to realize this, first, the nanostructured sensing film is synthesized over a short length of a centrally decladded straight and uniform optical fiber and then a comprehensive experimental investigation is carried out to optimize the design configuration/parameters of the nanostructured sensing film and to achieve the best possible sensor response. Much improved sensitivity of 27.1 mV/%RH is observed for the optimized sensor along with a throughout-linear sensor response over a dynamic range as wide as 24% to 95%RH with an average response time of 0.01 s for humidification and 0.06 s for desiccation. In addition, the sensor exhibits a very good degree of reversibility and repeatability. PMID:22534929

Based on resonant and waveguiding properties of optical microfiber loops, we theoretically investigated silica microfiber loop resonators (MLRs) for refractive index (RI) and salinity sensing of seawater. Dependences of sensitivity and detection limit on probing wavelength, fiber diameter, and ring diameter are calculated with typical parameters of seawater. Our results show that the sensitivity of MLRs increases with the increasing wavelength and the decreasing diameter of the microfiber. Bending loss and absorption loss are both important factors to determine the detection limit. By optimizing the parameters of the sensing system, RI sensitivity and salinity detection limit can reach 10(-6) RI units (RIU) and 10(-2) ‰ (10 ppm), respectively. The model presented here may be helpful for developing microscale fiber sensors for seawater detection with high sensitivity, low detection limit, and miniaturized sizes. PMID:22614605

Maximization of a projected laser beam's power density at a remotely located extended object (speckle target) can be achieved by using an adaptive optics (AO) technique based on sensing and optimization of the target-return speckle field's statistical characteristics, referred to here as speckle metrics (SM). SM AO was demonstrated in a target-in-the-loop coherent beam combining experiment using a bistatic laser beam projection system composed of a coherent fiber-array transmitter and a power-in-the-bucket receiver. SM sensing utilized a 50 MHz rate dithering of the projected beam that provided a stair-mode approximation of the outgoing combined beam's wavefront tip and tilt with subaperture piston phases. Fiber-integrated phase shifters were used for both the dithering and SM optimization with stochastic parallel gradient descent control. PMID:22825139

Incipient fault diagnosis is closely related to insulation condition assessment. A great number of methods are available for condition monitoring and diagnosis of power transformer insulation systems, but only few of them can take direct measurements inside the transformer. Fiber optic sensors can be applied to incipient fault diagnosis. In particular, acoustic sensors have been developed for detection and location of partial discharges in oil-filled power transformers. We report the study of extrinsic and intrinsic fiber Fabry-Pérot sensors that can be used to detect the acoustic waves that are generated by a partial discharge inside a power transformer. A comparative analysis is done to determine the best sensing head configuration and some methods to improve the parameter readout sensitivity are proposed. The sensing head behaviour when immersed in different fluids (air, water, and oil) is also investigated.

In the present paper, a laser-coupled optical fiber is introduced for pH sensing of Methyl red solution in the Ethanol solvent. Then it is modified for corrosion detection when it was placed inside a corrosive solution. Second-harmonic (SH) radiation of a microchip Q-switched pulsed Nd:YAG laser operating at ?=532 nm is generated via KTP nonlinear crystal, and it is launched into the fabricated fiber sensor. The provided evanescent field is absorbed by the surrounding environment in the sensing region, and the output intensity of the absorbed laser beam is monitored and recorded in the presence of the different kind of solvents and corrosive solutions. To increase the sensitivity of the pH sensor the fiber-optic probe is coiled and fixed on a Poly Propylene (PP) mount with 6 cm diameter and 10 cm long. The fabricated sensor is then calibrated for pH measurement of unknown media. For corrosion detection, a spin motor is used to uniformly coat a small portion of the fiber designed as U-shaped after its clad was removed by a simple chemical method. It is then electroplated by a very thin Fe-C film to form a corrosion sensor. It is observed that while the concentration of the NH4Cl solution is changed from 0.068 to 0.125 mol/l and its pH from zero to 14, the output intensity of the launched laser is increased due to the Fe-C film corrosion.

Optical fluorescence sol-gel sensors have been developed for the detection of carbon dioxide gas in the 0.03-30% range with a detection limit of 0.008% (or 80 ppm) and a quantitation limit of 0.02% (or 200 ppm) CO(2). Sol-gels were spin-coated on glass slides to create an organically modified silica-doped matrix with the 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) fluorescent indicator. The luminescence intensity of the HPTS indicator (513 nm) is quenched by CO(2), which protonates the anionic form of HPTS. An ion pair technique was used to incorporate the lipophilic dye into the hydrophilic sol-gel matrix. TiO(2) particles (<5 microm diameter) were added to induce Mie scattering and increase the incident light interaction with the sensing film, thus increasing the signal-to-noise ratio. Moisture-proof overcoatings have been used to maintain a constant level of water inside the sensor films. The optical sensors are inexpensive to prepare and can be easily coupled to fiber optics for remote sensing capabilities. A fiber-optic bundle was used for the gas detection and shown to work as part of a multianalyte platform for simultaneous detection of multiple analytes. The studies reported here resulted in the development of sol-gel optical fluorescent sensors for CO(2) gas with sensitivity below that in the atmosphere (ca. 387 ppm). These sensors are a complementary approach to current FT-IR measurements for real-time carbon dioxide detection in environmental applications. PMID:20038093

... Information and Communications Biology and Biomedical Engineering Optical and Photonic Materials and ... Optical Processing and Manufacturing Instrumentation and Sensing NSF-Wide Initiative in Optical ...

Topics covered include: Induction Charge Detector with Multiple Sensing Stages; Generic Helicopter-Based Testbed for Surface Terrain Imaging Sensors; Robot Electronics Architecture; Optimized Geometry for Superconducting Sensing Coils; Sensing a Changing Chemical Mixture Using an Electronic Nose; Inertial Orientation Trackers with Drift Compensation; Microstrip Yagi Antenna with Dual Aperture-Coupled Feed; Patterned Ferroelectric Films for Tunable Microwave Devices; Micron-Accurate Laser Fresnel-Diffraction Ranging System; Efficient G(sup 4)FET-Based Logic Circuits; Web-Enabled Optoelectronic Particle-Fallout Monitor; SiO2/TiO2 Composite for Removing Hg from Combustion Exhaust; Lightweight Tanks for Storing Liquefied Natural Gas; Hybrid Wound Filaments for Greater Resistance to Impacts; Making High-Tensile-Strength Amalgam Components; Bonding by Hydroxide-Catalyzed Hydration and Dehydration; Balanced Flow Meters without Moving Parts; Deflection-Compensating Beam for Use inside a Cylinder; Four-Point-Latching Microactuator; Curved Piezoelectric Actuators for Stretching Optical Fibers; Tunable Optical Assembly with Vibration Dampening; Passive Porous Treatment for Reducing Flap Side-Edge Noise; Cylindrical Piezoelectric Fiber Composite Actuators; Patterning of Indium Tin Oxide Films; Gimballed Shoulders for Friction Stir Welding; Improved Thermal Modulator for Gas Chromatography; Nuclear-Spin Gyroscope Based on an Atomic Co-Magnetometer; Utilizing Ion-Mobility Data to Estimate Molecular Masses; Optical Displacement Sensor for Sub-Hertz Applications; Polarization/Spatial Combining of Laser-Diode Pump Beams; Spatial Combining of Laser-Diode Beams for Pumping an NPRO; Algorithm Optimally Orders Forward-Chaining Inference Rules; Project Integration Architecture; High Power Amplifier and Power Supply; Estimating Mixing Heights Using Microwave Temperature Profiler; and Multiple-Cone Sunshade for a Spaceborne Telescope.

Particulate composite materials are very common in industrial applications due to the fact that particulate fillers can provide improved materials, as compared with the unfilled matrix. They can also be synergistic with fiber reinforcement to further improve the system performance. On the other hand, a new approach in structural health monitoring is to exploit the intrinsic properties of the material, such as electrical conductivity, optical properties etc, as sensing parameters. In this paper we present results concerning the strain sensing capabilities of iron/epoxy particulate composites at different percentages varying from 30% to 60% by weight. In particular, we investigate the strain induced alteration of the magnetic resistance (reluctance) of such polymers. The magnetic properties of the iron/epoxy composites have been investigated using a vibrating sample magnetometer at room temperature. For the strain-reluctance measurements, a non-contact sensing probe has been employed. The strain-reluctance relation is found to be linear and strongly dependent on the concentration of iron particles.

Graphene is a zero band-gap semi-metal with remarkable electromagnetic and mechanical characteristics. This study is the first ever attempt to use graphene in the surface plasmon resonance (SPR) sensor as replacement material for gold/silver. Graphene, comprised of a single atomic layer of carbon, is a purely two-dimensional material and it is an ideal candidate for use as a biosensor because of its high surface-to-volume ratio. This sensor is based on the resonance occasion of the surface plasmon wave (SPW) according to the dielectric constants of each metal film and detected material in gas or aqueous phase. Graphene in the SPR sensor is expected to enlarge the range of analyte to bio-aerosols based on the superior electromagnetic properties of graphene. In this study, a SPR-based fiber optic sensor coated with multi-layered graphene is described. The multi-layered graphene film synthesized by chemical vapor deposition (CVD) on Ni substrate was transferred on the sensing region of an optical fiber. The graphene coated SPR sensor is used to analyze the interaction between structured DNA biotin and Streptavidin is analyzed. Transmitted light after passing through the sensing region is measured by a spectrometer and multimeter. As the light source, blue light which of 450 to 460 nm in wavelength was used. We observed the SPR phenomena in the sensor and show the contrary trends between bare fiber and graphene coated fiber. The fabricated graphene based fiber optic sensor shows excellent detection sensitivity of the interaction between structured DNA and Streptavidin. PMID:22966575

In this study, we developed an embedded infrared fiber-optic temperature sensor for thermometry in high temperature/pressure and water-chemistry environments by using two identical silver-halide optical fibers. The performance of the fabricated temperature sensor was assessed in an autoclave filled with an aqueous coolant solution containing boric acid and lithium hydroxide. We carried out real-time monitoring of the infrared radiation emitted from the signal and reference probes for various temperatures over a temperature range from 95 to 225 °C. In order to decide the temperature of the synthetic coolant solution, we measured the difference between the infrared radiation emitted from the two temperature-sensing probes. Thermometry with the proposed sensor is immune to any changes in the...

A fiber-optic microphobe is described which is inexpensive and simple to build and use. It consists of an 80-micrometers optical fiber which at the end is tapered down to a rounded sensing tip of 20-30-micrometers diameter. The detector is a hybrid photodiode/amplifier. The probe has a sensitivity of 0.01 microEinst m-2 s-1 and a spectral range of 300-1,100 nm. Spectral light gradients were measured in fine-grained San Francisco Bay sediment that had an undisturbed diatom coating on the surface. The photic zone of the mud was only 0.4 mm deep. Measured in situ spectra showed extinction maxima at 430-520, 620-630, 670, and 825-850 nm due to absorption by chlorophyll a, carotenoids, phycocyanin, and bacterio-chlorophyll a. Maximum light penetration in the visible range was found in both the violet and the red or = 700 nm.

The sensing head of a two-color band ratioing pyrometer of a known type using a fiber optic cable to couple radiation to dual detector photodiodes is improved to have high spatial resolution by focusing the radiation received through an objective lens (i.e., by focusing the image of a target area) onto an opaque sheet spaced in front of the input end of the fiber optic cable. A two-mil hole in that sheet then passes radiation to the input end of the cable. The detector has two channels, one for each color band, with an electronic-chopper stabilized current amplifier as the input stage followed by an electronic-chopper stabilized voltage amplifier.

U-bend optical fiber probes have been shown to be very responsive to refractive index variations around the core, which makes them ideally suited for biosensor applications. Similar U-shaped polymer waveguides have also been fabricated using standard micro-fabrication technology. In the present study, suitable bend radii for such U-shaped embedded polymer waveguide probes have been determined for bio/chemical sensing applications. Although the effect of bend radii have been studied earlier for U-bend optical fiber sensors, such an investigation has not yet been performed for embedded bent waveguides. A single step fabrication procedure was performed to pattern SU-8 photo resist into semicircular C-shaped waveguides (of various bending diameters) interfacing a microchannel network and endin...

We propose a hybrid network that combine point and distributed Brillouin sensors in an architecture that also deploys remote distributed Raman amplification to extend the sensing range. A 46-km proof-of-concept network is experimentally demonstrated integrating point vibration sensors based on fiber-optic tapers, with distributed temperature sensing along the network bus. The sensor network with a double-bus topology offers a higher optical signal to noise ratio and dynamic range than a single-bus for intensity point multiplexed sensors. In this network, we include low-cost intensity sensors that are able to measure vibrations in the 0.01 to 50 Hz frequency range, which are important in the monitoring of large infrastructures such as pipelines.

To meet the requirements of outdoor field mineral analysis and remote sensing ground verification spectral analysis, the wide-range fiber spectral instrument covering 400 nm-2 500 nm was developed. The present article illustrates the design of the optical, mechanical and electrical parts of the instrument. The optical system utilizes grating horizontal-reflecting light route to implement the full coverage of the spectrum. Three line-array sensors are intercrossed in three directions on the spectrum surface to sense different spectrum ranges. CPLD device generates the sampling and driving temporal logic signals to the three line-array photoelectrical devices. Fourteen bits high speed AD converts the analog signals into digital ones. USB 2.0 is used for communication. The final results demonstrate that while implementing the measurement of wide spectrum, the instrument is improved in size, spectrum resolving power, signal quality and measuring speed. Ideal spectrum data were acquired. PMID:20672646

Unlike silicon microelectronics, photonics packaging has proven to be low yield and expensive. One approach to make photonics packaging practical for low cost applications is the use of {open_quotes}smart{close_quotes} packages. {open_quotes}Smart{close_quotes} in this context means the ability of the package to actuate a mechanical change based on either a measurement taken by the package itself or by an input signal based on an external measurement. One avenue of smart photonics packaging, the use of polysilicon micromechanical devices integrated with photonic waveguides, was investigated in this research (LDRD 3505.340). The integration of optical components with polysilicon surface micromechanical actuation mechanisms shows significant promise for signal switching, fiber alignment, and optical sensing applications. The optical and stress properties of the oxides and nitrides considered for optical waveguides and how they are integrated with micromechanical devices were investigated.

We propose a fiber optic sensor array based on bend loss assessed by optical time domain reflectometry (OTDR). The sensor mechanism is based on optical fiber bending loss compressed by external pressure. An elastomeric surface is applied to the sensor in order to communicate external pressure to the fiber coil and also, this make sensor able to deal with degradation coming from aggressive environments. The sensing system proposed is able to monitor liquid or gas pressure in different environments, such as water, oil, alcohols, some diluted acids and others, depending only of elastomeric membrane choice. In order to protect the sensor stage against environmental degradation a plastic packaging was chosen. Bend loss measurements is taken concerning the number of fiber loops involved in the sensor, pump signal wavelength and temporal width. This long for the best parameters in the sensor construction. The specific case of the sensor applied to water percolation monitoring from embankment damns is detailed in this paper; for this application the sensor array have a number of at least six stages totally independent each other, in such a way that each stage can be developed to monitor a specific environment. Sensors have shown good performance in field tests, reaching work range from 0.1 to 0.6 atm with 0.05 atm of precision.

By now, fiber Bragg gratings (FBGs) represent a well assessed technology in both communications and sensing fields. In particular, thanks to their small signal bandwidth and wavelength encoded information, they allow simple measurements in reflection for sensing purposes and also easy multiplexing capability in realizing sensors arrays. Unfortunately, to make FBGs sensitive to surrounding refractive index (SRI), hosting fiber structuring is needed. In last years, also tilted FBGs (TFBGs) - intrinsically SRI sensitive structures - have been proposed as promising technological platform for several sensing applications. However, complex spectral features combined with the difficulty to be configured as quasi distributed or multi-point sensors network limit the practical exploitation of this assessed and mature technology. It would be extremely useful to merge the peculiar spectral characteristics of both grating types. To address this issue, here, we propose a hybrid cavity involving two unbalanced uniform FBGs written at both sides of a TFBG to form an all-fiber interferometer. The proposed configuration provides a wavelength gated reflection signal with interference fringes depending on the cavity features modulated by spectral dips associated to the wavelength dependent optical losses due to cladding mode coupling occurring along the TFBG. Such a structure preserves the advantages of uniform FBGs in terms of interrogation methods and allows the possibility to contemporarily measure multiple parameters.

Based on the principle of the fiber Bragg grating strain sensor as well as the volume expansion of the reinforcing steel due to corrosion, an optical fiber grating sensor for monitoring corrosion of reinforcing steel and the method of temperature compensation were studied in the present paper. The sensor construction is that one Bragg grating is stuck on the inner center of two bars against each other, and the reinforcement volume as well as the diameter will expand due to corrosion. Based upon sensing mechanism, monitoring will be carried out by transforming the diameter increase to the fiber strain, and as a result the degree and rate of reinforcement corrosion can be obtained. The principle of corrosion monitoring is that the strain induced by corrosion and temperature fluctuation is measured by a reinforcing steel fiber grating sensor. At the same time, the strain induced by temperature fluctuation is also measured by an individual stainless fiber grating sensor. Therefore by two independent fiber grating sensors, the volume changed by corrosion can be separated. By the concrete encapsulating and embedding method of FBG corrosion sensor, the degree of corrosion of reinforcing reinforcement will be measured directly, which is not affected by corrosion factors and can be used in the early corrosion monitoring of reinforcement in concrete structures. Finally the relationship between corrosion rate and shift in center wavelength was calibrated by experiment. PMID:20302133

The purpose of this LDRD was to study the effect of steady-state neutron and gamma irradiation on the transmission of waveguides designed to operate well in the near- or mid-IR region of the electromagnetic spectrum. In this context, near-IR refers to the region between 1.3 {mu}m and about 2.4 {mu}m, and mid-IR between 3.0 {mu}m and 4.5 {mu}m. Such radiation environments could exist in nuclear power plants or nuclear weapons. Pulsed and steady-state radiation effects had been extensively studied on silica-based optical fibers because they have been the most readily available, most widely used in communications and sensing, and the least expensive. However, silica-based fibers do not transmit well beyond about 1.8 {mu}m and they are virtually opaque in the mid-IR. The mid-IR, as defined above, and beyond, is where vibrational spectroscopy is carried out. This type of sensing is one important application of infrared optical fibers.

Oxygen and carbon dioxide sensors are involved in many chemical and biochemical reactions. Consequently, considerable efforts over years have been devoted to discover and improve suitable techniques for measuring gas concentrations by optical fiber sensors. Optical gas sensors consist of a gas-sensitive dye entrapped in a matrix with a high permeability to gas. With such sensors, gas concentration is evaluated based upon the reduction in luminescence intensity caused by gas quenching of the emitting state. However, the luminescence quenching effect of oxygen is highly sensitive to temperature. Thus, a simple, low-cost plastic optical fiber sensor for dual sensing of temperature and oxygen is presented. Also, a modified Stern-Volmer model is introduced to compensate for the temperature drift while the temperature is obtained by above dual sensor. Recently, we presented highly-sensitive oxygen and dissolved oxygen sensors comprising an optical fiber coated at one end with platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and PtTFPP entrapped core-shell silica nanoparticles embedded in an n-octyltriethoxysilane(Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. Also, two-dimensional gas measurement for the distribution of chemical parameters in non-homogeneous samples is developed and is of interest in medical and biological researches.

A Fiber-Optic Localized Surface Plasmon Resonance (FO LSPR) sensor was fabricated using spherical gold nanoparticles (Au NPs) on a flattened end-face of the optical fiber. The Au NPs were easily synthesized by the Turkevich method and were immobilized on the end-face of the optical fiber by using a self-assembled monolayer (SAM). In order to examine the possibility of its application as a biosensor for label-free immunoassays, the fabricated FO LSPR sensor was used for the detection of the antibody-antigen reaction of interferon-gamma (IFN-?) and the limit of detection (LOD) was approximately 2pg/ml. Herein, The antibodies and bovine serum albumins (BSAs) were immobilized on the Au NPs by physisorption. Also, the FO LSPR sensor was used for the detection of a prostate-specific antigen (PSA) and the LOD was 1pg/ml below. The fabricated FO LSPR sensor can be used for real-time label-free immunoassay having fast detection time, high resolution and sensitivity. In addition, the proposed sensor platform has the advantages of low cost, simple optical setup, remote sensing, simple fabrication, real-time detection, low sample volume, and potential application to in-vivo detection systems. PMID:22951530

In this paper, the structural health monitoring of a pre-stressed concrete (PC) structure based on two types of distributed sensing techniques is addressed. The sensing elements are Brillouin scattering-based fiber optic sensors (FOSs) and HCFRP (hybrid carbon fiber reinforced polymer) sensors composed of three types of carbon tows. Both types of sensors are characterized by a broad-based and distributed sensing function. The HCFRP sensors are bonded on PC tendon, steel reinforcing bar, and embedded in tensile and compressive concrete sides with epoxy resins and putties. The FOSs are embedded in the tensile and compressive concrete sides where the HCFRP sensors are embedded as well. The distributed sensors are arranged to detect and monitor the initiation and propagation of cracks, yielding of steel reinforcements and corrosion of PC tendons. The experimental investigations demonstrate that the initiation and location of cracks, yielding of steel reinforcements, corrosion of PC tendons and structural health of PC structures can be effectively detected and monitored with such kinds of distributed sensing systems.

Real time monitoring of the mechanical integrity and stresses on key aerospace composite structures like aircraft wings, walls of pressure vessels and fuel tanks or any other structurally extended components and panels as in space telescopes is very important to NASA. Future military and commercial aircraft as well as NASA space systems such as Space Based Radar and International Space Station will incorporate a monitoring system to sense any degradation to the structure. In the extreme flight conditions of an aerospace vehicle it might be desirable to measure the strain every ten centimeters and thus fully map out the strain field of a composite component. A series of missions and vehicle health management requirements call for these measurements. At the moment thousands of people support a few vehicle launches per year. This number can be significantly reduced by implementing intelligent vehicles with integral nervous systems (smart structures). This would require maintenance to be performed only as needed. Military and commercial aircrafts have an equally compelling case. Maintenance yearly costs are currently reaching astronomical heights. Monitoring techniques are therefore required that allow for maintenance to be performed only when needed. This would allow improved safety by insuring that necessary tasks are performed while reducing costs by eliminating procedures that are costly and not needed. The advantages fiber optical sensors have over conventional electro-mechanical systems like strain gauges have been widely extolled in the research literature. These advantages include their small size, low weight, immunity to electrical resistance, corrosion resistance, compatibility with composite materials and process conditions, and multiplexing capabilities. One fiber optic device which is suitable for distributed sensing is the fiber Bragg grating (FBG). Researchers at NASA MSFC are currently developing techniques for using FBGs for monitoring the integrity of advanced structural materials expected to become the mainstay of the current and future generation space structures. Since carbon-epoxy composites are the materials of choice for the current space structures, the initial study is concentrated on this type of composite. The goals of this activity are to use embedded FBG sensors for measuring strain and temperature of composite structures, and to investigate the effects of various parameters such as composite fiber orientation with respect to the optical sensor, unidirectional fiber composite, fabrication process etc., on the optical performance of the sensor. This paper describes an experiment to demonstrate the use of an embedded FBG for measuring strain in a composite material. The performance of the fiber optic sensor is determined by direct comparison with results from more conventional instrumentation.

Fiber-based optical amplifiers such as the erbium-doped fiber amplifier(EDFA) and Raman fiber amplifier (RFA) offer the attraction of high gain, low coupling loss and polarization insensitivity. Hence their use in combination to form a nonregenerative rep...

temperature measurements with fiber optic Bragg gratings. ... One of the particularly important areas is the inspection of graphite fiber reinforced composite ... where neff is the effective refractive index of the fiber core and ? the grating period.

In this paper we investigate the temperature characteristic of an optical microfiber coil resonator (OMCR) which is wrapped on Teflon coated PMMA rob and embedded in low index polymer Teflon. The micro fiber used to fabricated the OMCR was 4 ~ 5?m in diameter and 14 mm in waist region length. The PMMA rob has a diameter of 2 mm. Our sample shows high temperature sensitivity as much as 80 pm/°C. The test result suggests OMCR could be of good value in application of temperature sensing.

Sasol Ltd.`s Mossgas plant, in Mossel Bay, South Africa, is using fiber optic sensing technology to detect potentially hazardous hot spots in its secondary methane reformers. The system is part of a distributed temperature system (DTS) that warns operators when hot spots begin forming. Without such warning, the localized high temperatures could lead to vessel damage or even process shutdown. The Mossgas DTS installation was described in an unpublished report by its manufacturer, York Sensors Ltd., Southampton, U.K. This paper summarizes this report.

Disclosed is a method and the resulting product thereof comprising a solid light-conducting fiber with a point of attachment and having a textured surface site consisting a textured distal end prepared by being placed in a vacuum and then subjected to directed hyperthermal beams comprising oxygen ions or atoms. The textured distal end comprises cones or pillars that are spaced upon from each other by less than 1 micron and are extremely suitable to prevent cellular components of blood from entering the valleys between the cones or pillars so as to effectively separate the cellular components in the blood from interfering with optical sensing of the glucose concentration for diabetic patients.

In this paper, recent research and application activities on smart sensing, monitoring, and damage detection for civil infrastructures are briefly introduced. Emphasis is given to the activities in Korea. First, the state of the art in smart sensors technology is reviewed including optical fiber sensors, piezoelectric sensors, and wireless sensors. Then, a brief overview is given to the recent advances in the structural monitoring/damage detection techniques such as ambient vibration-based bridge health evaluation, piezoelectric sensors-based local damage detection, wireless sensor networks and energy harvesting, and wireless power transmission by laser/optoelectronic devices. Finally, recent collaborative R&D activities on smart structure technologies in Korea are discussed, which have be...

We prove a representation formula for solutions of Schrödinger equations with potentials multiplied by a temporal real-valued white noise in the Stratonovich sense. Using this formula, we obtain a dispersive estimate which allows us to study the Cauchy problem in L2 or in the energy space of model equations arising in Bose–Einstein condensation, Abdullaev et al (2001 Nonlinearity and Disorder: Theory and Applications (NATO Science Series vol 45) ed F Abdullaev et al (Dodrecht: Kluwer)), or in fiber optics, Abdullaev et al (2000 Physica D 135 369–86). Our results also give a justification of diffusion-approximation for stochastic nonlinear Schrödinger equations.

In this work, we propose a novel fiber sensor that is based on an air-gap long-period fiber grating (AG-LPG), which is fabricated by combining fiber side polishing with fiber lithography. Its sensing mechanism is based on the loss-peak wavelength shift of the AG-LPG as the refractive index around the sensing head varies. Experimental results show that the maximum sensitivity is 620 nm/unit index (1.1 nm/%) in the sensing of various sugar solution concentrations. This novel sensing head provides a simple, reliable, repeatable, accurate, and nondestructive approach for detecting various chemical solutions and mixing gases and for biomedical applications.

The vision of intelligent and large-area fabrics capable of signal processing, sensing and energy harvesting has made incorporating electronic devices into flexible fibers an active area of research. Fiber-integrated rectifying junctions in the form of photovoltaic cells and light-emitting diodes (LEDs) have been fabricated on optical fiber substrates. However, the length of these fiber devices has been limited by the processing methods and the lack of a sufficiently conductive and transparent electrode. Their cylindrical device geometry is ideal for single device architectures, like photovoltaics and LEDs, but not amenable to building multiple devices into a single fiber. In contrast, the composite preform-to-fiber approach pioneered in our group addresses the key challenges of device density and fiber length simultaneously. It allows one to construct structured fibers composed of metals, insulators and semiconductors and enables the incorporation of many devices into a single fiber capable of performing complex tasks such as of angle of incidence and color detection. However, until now, devices built by the preform-to-fiber approach have demonstrated only ohmic behavior due to the chalcogenide semiconductor's amorphous nature and defect density. From a processing standpoint, non-crystallinity is necessary to ensure that the preform viscosity during thermal drawing is large enough to extend the time-scale of breakup driven by surface tension effects in the fluids to times much longer than that of the actual drawing. The structured preform cross-section is maintained into the microscopic fiber only when this requirement is met. Unfortunately, the same disorder that is integral to the fabrication process is detrimental to the semiconductors' electronic properties, imparting large resistivities and effectively pinning the Fermi level near mid-gap. Indeed, the defect density within the mobility gap of many chalcogenides has been found to be 1018-1019 cm-3 eV-1, resulting in a narrow depletion width and ohmic behavior at metal-semiconductor junctions. In this work we incorporated phase-changing semiconductors, those that may be easily converted between the amorphous and crystalline states, into composite fibers with a goal towards constructing rectifying junctions in fiber.

... from x-rays, we also do a fiber optic examination , which is a small spaghetti like structure ... and that’s followed by a fluoroscopy or fiber optic examination to look at the fine motor skills ...

A tunable single-longitudinal-mode (SLM) fiber optical parametric oscillator is demonstrated by using a subring cavity and a fiber loop mirror incorporated with a saturable absorber. It can provide dual-wavelength SLM output. © 2010 Optical Society of America.

Detector 1. Comm. Detector 2. Dichroic. 50-50. Splitter. Polarizing. Combiner ..... wealth of development in fiber-optics technology [19] Use of fiber optics in the ...... rectangular, tapered, and hollow waveguide geometries are possible with this ...

Fiber-optical accelerometers based on polymer optical fiber Bragg gratings (FBGs) are reported. We have written 3mm FBGs for 1550nm operation, characterized their temperature and strain response, and tested their performance in a prototype accelerometer.

Sep 19, 2012 ... Chemical stripping of optical fibers: The stripping fixture holds a cable ... Optical fiber connector polishing: This device controls connector ... or affected by contact with most chemical stripping solutions; Simple: Is easy to use ...