Optical sensors that can be used in harsh environments are desirable in a wide range of industrial and military applications where conventional measurement devices are difficult to apply due to the harsh environments. Optical fiber sensors have been demonstrated to be attractive for the measurement of a wide variety of physical parameters because of such inherent advantages as 1) small size, 2) an immunity to electromagnetic interference, 3) high resolution, 4) non-electrically conducting, 5) capability of responding to a wide variety of measurands, 6) avoidance of electric sparks, 7) resistance to harsh environment, 8) remote operation, and 9) capability of multiplexing. In the past two decades, fiber sensors have been demonstrated and developed. The optical sensor research at the Virginia Tech Center for Photonics Technology (VTCPT) has been mainly focused on the development of sensors for measurement of pressure, temperature, strain, acoustic waves, flow, electric partial discharges, surface mapping and 3-D temperature imaging. Most of these sensors are based on optical fibers, including silica glass fiber with various polymer and metallic coatings and single-crystal sapphire fiber waveguides. In terms of the optical parameters being modulated, these sensors could be approximately classified into interferometric, polarimetric, intensity-based, and wavelength-coded devices. This paper presents several examples of the sensors recently developed at Virginia Tech.

This paper presents a brief overview of research activities in fiber optic sensors at the Applied Physics Division of the Scientific Center CICESE. Started in 1992, the research was directed to develop a new wavelength scanning technique for multiplexing and interrogation of a serial array of interferometric sensors in polarization-maintaining fiber. A further developing of this technique resulted in a new approach for multiplexing and demodulation of Bragg grating-based sensors. A novel algorithm has been developed for digital demodulation of the twin-grating sensor, which provides absolute high resolution measurements in a wide dynamic range. Recent experiments on testing a twin grating fiber optic sensor demonstrate very promising results. A few other developed sensing techniques are also presented in this paper.

This paper presents recent developments in the use of optical frequency domain reflectometry (OFDR) to measure engineering parameters at thousands of locations along optical sensing fibers where weakly reflecting Bragg gratings have been photoetched. Application of the sensing fibers outside of the development lab has revealed several areas for improvement. Some of the problems encountered include polarization fading, non-linear laser tuning, and sensor calibration. This paper considers the use of polarization diversity detection and monitoring of the laser tuning characteristics to provide a more robust OFDR system for both sensor calibration and measurement. Possible modifications to the system are reported along with calibration measurements for quantifying the effects of polarization fading in the sensing fiber.

We have proposed and developed a technique to synthesize optical coherence function into arbitrary shapes. By using the technique, Synthesis of Optical Coherence Function, distributed sensing schemes can be provided without any mechanical moving parts nor calculation. Applying the technique, we have proposed and studied a scheme to diagnose fiber optic subscribe networks. Fiber optic distributed stress sensing systems have also been constructed, which are applicable to smart structures and security systems. By also applying a similar way, we have proposed a system to measure the strain distribution along an optical fiber through the Brillouin scattering caused in the fiber. In all the schemes, we do not use a pulsed-lightwave but use a continuous-wave, whose correlation is controlled by FM or PM modulation onto lightwaves, to have the distributed sensing function. By these correlation-based continuous-wave techniques, quite a high spatial resolution and other superior functions to the pulsed-lightwave technique have been realized. These systems can achieve a cm order spatial resolution, which is suitable for smart materials.

The paper reviews the adoption of distributed temperature sensing (DTS) technology based on Raman backscatter. With one company alone having installed more than 400 units, the DTS is becoming accepted practice in several applications, notably in energy cable monitoring, specialised fire detection and oil production monitoring. The paper will provide case studies in these applications. In each case the benefit (whether economic or safety) will be addressed, together with key application engineering issues. The latter range from the selection and installation of the fibre sensor, the specific performance requirements of the opto-electronic equipment and the issues of data management. The paper will also address advanced applications of distributed sensing, notably the problem of monitoring very long ranges, which apply in subsea DC energy cables or in subsea oil wells linked to platforms through very long (e.g. 30km flowlines). These applications are creating the need for a new generation of DTS systems able to achieve measurements at up to 40km with very high temperature resolution, without sacrificing spatial resolution. This challenge is likely to drive the development of new concepts in the field of distributed sensing.

The paper describes research at Southampton University, aimed at optimizing the design of fibre-remoted dissolved-oxygen sensors, using immobilized fluorescent Ru²⁺ indicators. The design and construction of two types of fluorescence lifetime monitoring units, one type using phase-delay-monitoring and the other using photon-counting, is described. Results from a detailed theoretical study of a photon-counting RLD fluorescence lifetime sensor are presented, with specific attention to noise aspects. By numerical modeling of an analytical solution, the optimum time-window boundaries for the photon-counting system are identified. A surprising result is that the signal/noise can actually be improved by not using photon counts from all of the exponential decay, but leaving a time-gap in the measurement improves lifetime accuracy. Our previously reported Ti³⁺ - doped sapphire fluorescence-lifetime calibration probe is described, and a new method for RLD interrogator verification using the probe is demonstrated.

An overview is given on the activity in progress at IROE, relative to the field of optical fibre sensors for chemical parameters. Optode-based sensors are under development for both biomedical and environmental applications. As for the biomedical field, particular attention will be devoted to clinical applications of the developed sensor in gastroenterology. The first clinical applications of an absorption-based sensor for the detection of gastric carbon dioxide will be described. Clinical results have shown the superiority of the developed sensor over the sensor currently available on the market and based on air tonometry. New clinical findings involving a sensor for the detection of bile will be also discussed. As far as environmental applications are concerned, an optode for the detection of nitrogen dioxide will be described.

Novel approaches are required to coordinate the immense amounts of information derived from diverse genomes. This concept has influenced the expanded role of high-throughput DNA detection and analysis in the biological sciences. A high-density fiber optic DNA biosensor was developed consisting of oligonucleotide-functionalized, 3.1 mm diameter microspheres deposited into the etched wells on the distal face of a 500 micrometers imaging fiber bundle. Imaging fiber bundles containing thousands of optical fibers, each associated with a unique oligonucleotide probe sequence, were the foundation for an optically connected, individually addressable DNA detection platform. Different oligonucleotide-functionalized microspheres were combined in a stock solution, and randomly dispersed into the etched wells. Microsphere positions were registered from optical dyes incorporated onto the microspheres. The distribution process provided an inherent redundancy that increases the signal-to-noise ratio as the square root of the number of sensors examined. The representative amount of each probe-type in the array was dependent on their initial stock solution concentration, and as other sequences of interest arise, new microsphere elements can be added to arrays without altering the existing detection capabilities. The oligonucleotide probe sequences hybridize to fluorescently-labeled, complementary DNA target solutions. Fiber optic DNA microarray research has included DNA-protein interaction profiles, microbial strain differentiation, non-labeled target interrogation with molecular beacons, and single cell-based assays. This biosensor array is proficient in DNA detection linked to specific disease states, single nucleotide polymorphism (SNP's) discrimination, and gene expression analysis. This array platform permits multiple detection formats, provides smaller feature sizes, and enables sensor design flexibility. High-density fiber optic microarray biosensors provide a fast, reversible format with the detection limit of a few hundred molecules.

An improved refractive index microsensor based on surface plasmon resonance (SPR) for fine scale measurements in aquatic environments is presented. Furthermore this sensor should serve as a platform for different applications. In the first place refractive index measurements in marine environments have been performed to characterize the light conditions around photosynthetically active organisms. By scalar irradiance microprobes the light intensity can be investigated at a spatial resolution of 100micrometers . The presented sensor for refractive index achieves a spatial resolution better than 1mm. It covers a range of 1.30 and 1.38 refractive index units (RIU) with an accuracy of 5x10^-4 RIU. Due to this accuracy, the miniaturized geometry and the simple preparation the sensor can serve as a platform for chemo- and biosensors with a high spatial resolution and fast response. Therefor a suitable sensitive layer that converts the specific analyte concentration into a refractive index change can be deposited onto the gold surface. For that purpose swellable polymer microspheres are currently investigated. The sensor characteristics, measurement system, and applications are presented.

We report herein on the development of a FRET-based method to detect changes caused by viral protein-receptor binding. FRET fluorophore pairs (donor and acceptor fluorophores) were tagged to two specific receptors, both which bind to a viral protein. When the binding event occurs, the distance between the donor and acceptor FRET fluorophores is decreased, thus initiating the fluorescence resonance energy transfer (FRET). Since the binding event is unique to the viral protein, fluorescent change indicates the present of the virus. In this paper, the viral protein gp120, which is the featured protein on the surface of HIV-1, was detected. The receptors, CD4 and gp120-antibody which specifically bind to gp120, were conjugated to the FRET fluorophore pair, AMCA-NHS (succinimidyl-7-amino-4-methylcoumarin-3-acetic acid) and FITC (fluorescein isothiocyanate) respectively. Spectrofluorimetry was used to detect the fluorescent change between AMCA-NHS and FITC peak intensities when the receptors bind to the gp120. Specific binding gp120 and non-specific binding gp120 were used to test the selectivity of the sensor. The results indicated that FRET-conjugated receptors can efficiently detect the presence of gp120.

A new sensitive method based on bioinduced chemiluminescence and Daphnia as a test object is proposed for the evaluation of general toxicity of environment. The method was tested at the determination of biological toxicity of the solution of potassium chromate and at the control of water toxicity of some rivers of Ukraine. Special attention was paid to the optimization of conditions for the chemiluminescence determination. The medium of Daphnia staying was shown to have no spontaneous chemiluminescence. This was revealed using hydrogen peroxide and luminol, the optimal concentrations of which were 23 and 1.6x10^-2 mmol/L. p-Iodphenol at low concentrations (4x10^-5- 2x10^-3 mmol/L) did not effect chemiluminescence signal but at high concentrations (4x10^-2 mmol/L) an inhibition of chemiluminescence was observed. To obtain the needed intensity of chemiluminescence it is necessary to incubate no more than 5 Daphnia persons in volume of 10 mL of sample to be analyzed. The intensity of chemiluminescence of Daphnia staying medium and the sensitivity of this organism to potassium chromate increased at the temperature increasing from 24 to 32 degree(s)C. Medium of Daphnia staying can be preserved in refrigerator for several hours without loss of chemiluminescence signal.

An optical method has been proposed and successfully tested for direct detection of biochemical reactions on a surface, which is insensitive to variations of the radiation intensity and refractive index of a solution. The method is based on detection of the spectrum of the reflected or transmitted radiation modulated by the interference in a sensitive layer of large thickness (several tens and hundreds of microns), which can be a microscope cover glass with a deposited receptor layer. A change in the phase of the interference pattern in this spectrum is used as an information signal about a change in the thickness of the sensitive layer caused by a biochemical reaction. Single- and multichannel (up to 96 channels) devices have been designed to study reactions of binding and detachment of proteins in real time. The root-mean-square noise of the prototypes expressed in the layer thickness was 3 pm.

In this paper, we describe the design and development of a high sensitivity, large dynamic range force transducer capable of measuring transient force changes in tension and compression. Conventional force transducers typically rely on the deformation of strain gauges, or on servo-mechanical load cells. While strain gauge transducers exhibit a rapid response time, they are subject to electrical noise, and typically have a minimum useful limit of approximately 10^-5 N. Servo-mechanical transducers have poor response times and exhibit compliance in the axis of deformation that is unacceptable for many applications. The research objective is to develop a novel force transducer based on the change in optical properties with loading of a pre-stressed polymer. The concept utilizes a pre-stressed polymer material as a linkage to which a force would be applied either in compression or tension. The molecular deformation of the polymer linkage will be analyzed using miniature optical components arranged as a phase-modulated polarimeter capable of birefringence measurements on the order of 10^-9. Calibration of the measured birefringence with known loads provides the necessary calibration parameters. The instrument is capable of directional force measurements and is extremely accurate for measuring low-level forces. Since the force transducer is based on optical techniques, it would be resistant to electronic noise, and would allow measurement of rapidly changing loads. The best available force transducers capable of measuring transient responses have a lower resolution of approximately 10^-5 N. Research with the rheology of fluids, transient flows of pharmaceuticals in combinatorial research, biological tissue response, and biomimetic adhesive research often require force measurements below this range. Although ultra-microbalances exist that have sensitivities well below this range, the averaging techniques employed that allow these measurements make them unsuitable for transient flows, as does the physical size of the systems.

The purpose of a green leaf threshing (GLT) plant is to separate the tobacco leaf from the stem. In the GLT process, there are over a dozen parameters to adjust for optimal performance. The current laboratory measurement technique is destructive, laborious and not as well suited for optimizing processing parameters as an on-line technique. A machine vision technique was developed to non-destructively measure the amount of stem in the stream of processed tobacco leaf. The machine vision technique employs novel lighting to collect images and image processing to measure the amount of stem in the image. The image processing combines fuzzy logic and unique morphological image processing to extract the leaf from the background and then the stem present in the leaf. Performance of the optical technique compared favorably with the lab method. Correlation coefficient (R²) was greater than 0.95 and relative error (%RSD) was less than 6%.

A multi-ions co-doped probe had been developed for radiation-based high-temperature fiber-optic sensing. The heavily (Nd³⁺, Er³⁺ and Cr³⁺)-co-doped probe was fabricated on one end of an Y₂O₃-ZrO₂ waveguide by powder growth technique on an LHPG system. The wavelength-dependent absorption and emission spectra were measured, favorable results were obtained. In high temperature tests, the probe survived 2300 degree(s)C and showed a short-term stability at oxidative high temperature environment. The thermal response time of the probe is about 3.3s. Compared with metal- or oxide-coated probe, the doped probe demonstrated higher chemical and high-temperature stabilities.

Due to the foreseen possibility of technological applications, there is an increasing interest in nanocrystalline soft materials, especially in iron silicon alloys. The synthesis of nanoparticles by means of CO₂ laser induced pyrolisys is an important method for the production of the latter material with high purity upon well controlled conditions. In this production process, implying fast ultrafine powders condensation from the gas phase, the temperature is a key parameter, since the particles size is strongly affected by its variations. The potentialities of laser spectroscopic methods in the ultraviolet and infrared spectral region to monitor nanoparticles growth in a semi-industrial flow reactor for production of Si and FeSi nanoparticles and operating in ENEA, are explored in the present work.

Although Y₂O₃-ZrO₂ fiber-optic sensor has been developed for contact measurement of temperature higher than 2000 degree(s)C, its performance is not as good as that of sapphire fiber-optic sensor below 1900 degree(s)C due to the large optical loss of the Y₂O₃-ZrO₂ fiber. In order to improve the Y₂O₃-ZrO₂ fiber-optic sensor for ultra-high-temperature applications, in this work, based on a newly developed rectangular Y2O3-ZrO2 single-crystal waveguide with much lower optical loss, an improved Y₂O₃-ZrO₂ waveguide-fiber-optic sensor has been developed. The sensor has been tested up to near 2300 degree(s)C, we estimate that, the improved sensor has similar performance as the sapphire fiber-optic sensor in accuracy and resolution, except the disadvantage of relatively short waveguide. In addition, in this work, instead of the previous volatile and toxic BeO-coated probe, we use a multi-ions-doped sensor head, which is much stable and safe.

In this paper, we describe a detachable triangular-shaped bulk-optic glass sensor for three-phase current measurement using only one laser source. The sensor is constructed from three separate SF6 glass rods that form a triangle, where the coils of the three-phase current are mounted separately on the galas rods. Laser light is guided through the glass in a closed loop by reflecting twice at the critical angle at the two corners of the triangle. On the reflection surface of each corner, light is tapped with a right-angle prism that is pressed against the surface. The light beams tapped from the two corners and that emerging from the exit face of the sensor carry different components of the three- phase current. By processing these three light signals, the three phases of the current can be determined. To demonstrate the principle, an experimental sensor has been constructed and tested.

Detailed studies on fiber optic pressure and temperature sensors for oil down-hole applications are described in this paper. The sensor head is an interferometric based fiber optic senor in which the air-gap will change with the pressure or temperature. For high-speed applications, a novel self-calibrating interferometric/intensity-based (SCIIB) scheme, which realizes compensations for both the light source drift and the fiber loss variation, was used to demodulate the pressure (or temperature) signals. An improved white light system was developed for sensor fabrication. This system is also used as the signal demodulation system providing very high resolution. Experiment results show that the SCIIB system achieves 0.1% accuracy with a 0-8000psi working range for the pressure sensor and a 0-600 degree(s)C working range for the temperature sensor. The resolution of the white light system is about +/- 0.5 nm with a dynamic range up to 10 micrometers. The long -term testing results in the oil site are also presented in this paper.

With a single-crystal sapphire disk as the sensing element, a broadband polarimetric interferometer (BPI) based high temperature sensor is presented. The state of polarization of the broadband incident light is modulated by the birefringence of the sapphire disk and becomes a wavelength-encoded signal, which is detected by an optical spectrum analyzer (OSA). From the detected optical spectrum, an internally developed algorithm is employed to measure the difference of optical paths between two orthogonal linearly polarized lights in the sapphire disk, which is uniquely determined by environment temperature. A wide dynamic measurement range (from room temperature up to 1600 degrees Celsius) with a resolution less than 1 degree(s)C and accuracy 0.26% full scale is achieved. The great advantages of this sensor are its simplicity and long-term stability in the harsh environment.

Studies have shown that nitrogen oxides released to the atmosphere as a result of combustion processes can be linked to the formation of acid rain and ground level ozone (smog). Several different processes to reduce the amount of NOx (deNOx process) have been developed and applied. A common factor in all is the need to control the ammonia slip below the low PPM levels. The flue gas stream contains ammonia, nitrogen oxides and in some cases sulfur dioxide. These components all absorb UV radiation, and therefore can be monitored by a UV diode array process spectrometer. In some applications, however, the sulfur dioxide concentration in the gas can be too high to allow for the accurate and direct measurements of the ammonia slip. To overcome this difficulty a fast separation cell is utilized to remove the SO₂ from the stream prior to measurement. The analyzer measures the spectrum of the almost separated components; the spectra are then analyzed by a multicomponent method to give the concentration of the individual components. Withdrawing a representative sample across the stack is a crucial factor in this application; spatial averaging across the stack is obtained by drawing a sample through 12 holes with non-equal diameters. The spectroscopic methods, separation of stream components, and the in-situ sampling will be discussed.

This paper present a further development of electric field sensor and pressure sensor. They use new liquid crystal droplet materials. We discuss some of the features of devices formed from these materials. First of all, this material is a flexible plastic sheet, which can be readily polymerized to any thickness, size, or form. Devices formed from this material do not require sealing and can be fabricated as large, flexible plastic sheets that can be cut or trimmed. The principle of operation of sensors formed from thin films of this material is to regulate the light scattering properties of droplets of the birefringent liquid crystal by applications of an electric field. The electric field is which the material is sandwiched between glass or plastic sheets containing transparent conducting electrodes. In the absence of a voltage to the electrodes (off state), the optic axes of the microdroplets are randomly oriented as illustrated and scatter light. In this state the material appears an opaque white. Upon removal of the applied voltage, the large surface-area-to-volume ratio of the microdroplets allows surface interactions to return the nematic material to its random alignment and opaque texture. An electric field sensor is prepared using nematic liquid- crystal droplet materials and optical fiber systems. Transmission light intensity through the droplets is modulated by an ac electric field and its amplitude increases in good proportion to the electric field strength, covering a wide range. This paper presents a further development of a new fiber optic ion and high hydrostatic pressure sensing technique utilizing new classes of nematic liquid crystals droplets with a significantly reduced thermal sensitivity. The low- pressure sensor (up to 0.7 MPa) is based on polarization effects caused by strong rotary power of chiral nematics and pressure-induced deformations of a twisted nematic cell. The high-pressure sensor (up to 70 MPa) is based on intensity phenomena occurring in novel classes of chiral nematics with induced smectic phase. The latest results indicate that our method of hydrostatic pressure measurement offers high response to pressure with reduced temperature sensitivity.

In the design and testing of gas turbine engines, real-time data about such physical variables as temperature, pressure and acoustics are of critical importance. The high temperature environment experienced in the engines makes conventional electronic sensors devices difficult to apply. Therefore, there is a need for innovative sensors that can reliably operate under the high temperature conditions and with the desirable resolution and frequency response. A fiber optic high temperature sensor system for dynamic pressure measurement is presented in this paper. This sensor is based on a new sensor technology - the self-calibrated interferometric/intensity-based (SCIIB) sensor, recently developed at Virginia Tech. State-of-the-art digital signal processing (DSP) methods are applied to process the signal from the sensor to acquire high-speed frequency response.

Resource allocation and congestion control are two interrelated critical issues that arise in a task-oriented distributed sensor network. An effective resource management policy must account for these and their impact on the overall objectives of the network. In this paper, the viability of a virtual per-flow framework for addressing both resource allocation and congestion control in an integrated environment is demonstrated. In this framework, the resources being allocated to a physical buffer at a decision node are established by allocating and maintaining certain virtual resources to each incoming data flow. The virtual per-flow framework allows the design of controllers for each link independently of the others thus enabling a decoupled analysis and allowing one to incorporate different delay models and nonlinearities for each input data link. The effectiveness of the per-flow strategy is demonstrated via the design of a robust H_(infinity )-norm based feedback controller that ensures extremely good tracking of a dynamically changing set-point of a decision node buffer of a distributed sensor network. The design is robust against the time-varying and uncertain nature of network-induced delays.

A new signal processing approach for fiberoptical sensors, microoptodes, is presented. All signal generation and processing is completely based on a fast, low-cost DSP (Digital Signal Processor). This enables the implementation of new features such as a simultaneous multi-frequency measurement to resolve different analytical parameters in the luminescence signal. For instance, a hybrid sensor was applied to simultaneously sense the temperature and oxygen concentration, and the temperature information was used to compensate for the temperature effect on the oxygen measurement. As a further benefit, recent improvements in indicator chemistry and fiber tip preparation also yield a luminescence signal level high enough to be detected with a common photodiode instead of a photomultiplier tube. Consequently, the combination of small detectors and highly integrated DSPs enable portable, handheld measurement devices with very little calibration requirements.

Acquiring accurate, transient measurements in harsh environments has always pushed the limits of available measurement technology. Until recently, the technology to directly measure certain properties in extremely high temperature environments has not existed. Advancements in optical measurement technology have led to the development of measurement techniques for pressure, temperature, acceleration, skin friction, etc. using extrinsic Fabry-Perot interferometry (EFPI). The basic operating principle behind EFPI enables the development of sensors that can operate in the harsh conditions associated with turbine engines, high-speed combustors, and other aerospace propulsion applications where the flow environment is dominated by high frequency pressure and temperature variations caused by combustion instabilities, blade-row interactions, and unsteady aerodynamic phenomena. Using micromachining technology, these sensors are quite small and therefore ideal for applications where restricted space or minimal measurement interference is a consideration. In order to help demonstrate the general functionality of this measurement technology, sensors and signal processing electronics currently under development by Luna Innovations were used to acquire point measurements during testing of a transonic fan in the Compressor Research Facility (CRF) at the Turbine Engine Research Center (TERC), WPAFB. Acquiring pressure measurements at the surface of the casing wall provides data that are useful in understanding the effects of pressure fluctuations on the operation and lifetime wear of a fan. This measurement technique is useful in both test rig applications and in operating engines where lifetime wear characterization is important. The measurements acquired during this test also assisted in the continuing development of this technology for higher temperature environments by providing proof-of-concept data for sensors based on advanced microfabrication and optical techniques.

Recently developed optical fibers rely on an array of air holes in the cladding to confine light to the fiber core as opposed to conventional telecommunications fibers that require a refractive index difference produced by different composition glasses in the core and cladding regions. Holey fibers have been fabricated by drawing an array of tubes stacked around a solid central core. In this paper, we describe a new technique to produce the holes (or pores) in the cladding region. These new fibers have been made by drawing a preform, consisting of a porous outer cladding region surrounding a solid central core region, into a fiber. During the fiber drawing process, the pores initially present in the preform cladding region are drawn into small, long, thin tubular pores. Controlling the dimensions and distribution of the pores in the preform can control the physical dimensions and distribution of the pores in the fiber. In some of the preforms, the porous cladding region in the preform was prepared by sol gel techniques. The preform fabrication process and fiber drawing process used to produce these new holey fibers as well as the results of the morphological study elucidating the size, shape and distribution of the porous phase are presented.

Optical fibers are being used in an increasingly wider range of applications, some of which involve elevated temperature and pressure in the presence of water. Measurements of the penetration rate of water into optical fibers at elevated temperature (300 degree(s)C) and pressure (1440 psi) is presented for standard communication grade silica fiber and for protected fibers. The penetration rate was monitored in- situ using a broadband light source and an optical spectrum analyzer to measure the change in absorption over the spectral range from 400 to 1700 nm. Methods to protect the optical fibers from water penetration were also evaluated in the elevated temperature and pressure environment. Stress corrosion cracking data for fibers exposed to air at room temperature and pressure as well as dry and wet fiber treatments is also presented in terms of time to failure versus bend radius for selected environmental conditions. Effect of chemical treatments on the time to failure at fixed bend radius both for pre-water and post-water exposure is presented.

Over the past few years we have been developing applications for a high-resolution (sub-micron accuracy) fiber optic coupled dual Michelson interferometer-based instrument. It is being utilized in a variety of applications including monitoring liquid layer thickness uniformity on coating hoppers, film base thickness uniformity measurement, digital camera focus assessment, optical cell path length assessment and imager and wafer surface profile mapping. The instrument includes both coherent and non-coherent light sources, custom application dependent optical probes and sample interfaces, a Michelson interferometer, custom electronics, a Pentium-based PC with data acquisition cards and LabWindows CVI or LabView based application specific software. This paper describes the development evolution of this instrument platform and applications highlighting robust instrument design, hardware, software, and user interfaces development. The talk concludes with a discussion of a new high-speed instrument configuration, which can be utilized for high speed surface profiling and as an on-line web thickness gauge.

A new and simple optical gas cell, developed to perform as the transducer for a methane fiber optic sensor, is presented. Its main advantage lies in the fact that, employing low-cost components and an easy alignment process, the path where the light beam is in contact with the pollutant becomes maximized to as much as four times the physical length of the optical cell. This increment in optical length is directly related to the optimization of the fiber optic sensor since low levels of methane concentration can be measured as stated by Beer-Lambert's law. One of the main advantages of this design lies in the simplicity of the optic cell, which makes it very interesting when one has to deal with the manufacturing process. The cell is mounted on a reflective configuration which improves the connection as only one optical fiber is employed. The main elements of the cell are an optical fiber, a mirror of high reflectivity and a converging lens arranged in an appropriate fashion to obtain the desired result. With this relatively reduced and low cost set of devices the insertion losses achieved are in the range of the 4-5 dB's.

High quality Y₂O₃-ZrO₂ single crystal rectangular waveguides had been developed for high-temperature sensing applications. The waveguides were fabricated from bulky Y₂O₃ stabilized ZrO₂ single crystal by precise cut and fine polish. Three rectangular waveguides with cross-section larger than 1mmx1mm and length of 45mm~65mm were obtained. They showed much better optical properties than Y₂O₃-ZrO₂ single crystal fibers grown for fiber-optic sensing in previous work, optical losses of these waveguides were lower than 0.03dB/cm at wavelength of 900nm, and they were able to endure temperature as higher as 2300 degree(s)C. All of them survived a 10g vibration test with average STF(strain to failure) of about 0.25%. Experimental results show that, these waveguides are promising for fiber-optic sensing for temperature above 2000 degree(s)C.

A measurement system based on a single-mode fiber optic interferometer has been developed to simultaneously measure the vibrations in terms of velocity. The fiber interferometer reported has been realized with the purpose of using it as the basic measuring sensor of the system. One of its main features is that it is operated in the homodyne mode allowing the detection of the direction of motion without using Bragg cells or other optical or mechanical shifting devices, which usually present different inconveniences. The sensor has been calibrated against a commercial laser vibrometer. The first system prototype developed and presented in this work is capable to measure the vibration on two points simultaneously.

In this work we decided to show the behavior about the bend loss caused by soft and swellable materials. The principal measurements of fiber bend loss caused by soft and swellable materials were done with perturbation periods of 1 mm to 20 mm, because we needed to be close in the range of small curture. We used soft materials that have different moduli of Young. To accomplish this measure, we used single mode and multimode fibers. We had to watch the behavior over range of wavelength 1400nm to 1600nm with different radii of curvature. We would like to point out that the material that has the highest modulus of Young causes the highest loss. Ours results show that the highest attenuation and fastest sensor operation can be achieved at respectively long periods of perturbation, more than 10 mm in our experiments.

This work describes the performance of a new optical distributed sensor. This new sensor is capable of detecting and locating liquid hydrocarbon leakage on long pipelines. It is an improvement over the current fiber bending distributed sensors that use a polymeric filament that interacts with an optical fiber by means of a helicoidal wire. When a liquid or gas compatible with the polymeric filament within this type of sensor comes in contact with it, the liquid is absorbed and causes the swelling of the filament and the concomitant compression of the optical fiber against the helicoidal wire. This phenomena cause the fiber to bend and generate an increase on the optical attenuation signal that travels through the fiber. The signal attenuation permits the detection of a specific liquid presence in the vicinity of the sensor and the reflection of the same signal allows to pinpoint the location of this event. The new sensor has the following advantages over similar devices: a) the swelling of the polymeric filament is conducted in a preferential direction permitting to concentrate the osmotic pressure towards the optical fiber. This improves significantly the response speed of the sensor. b) The fiber is placed within a capillary channel located eccentrically in the polymer filament; therefore, no additional protection is needed to prevent damage to the fiber. Of even greater importance, the signal attenuation provoked by stress and deformations due to direct contact of the fiber with the helicoidal wire is avoided. And finally, c) an optimal bending period that take in count the polymer nature to improve the sensor response was found and employed. An experimental prototype of this sensor was fabricated using a multimode optical fiber attached to a polybutadiene filament. The experimental results confirm the benefits of this new design.

We present here a very fast, responsive fiber optic relative humidity (RH) sensor. The sensor was obtained by coating a thin PVA/CoCl₂ film on the core of a plastic cladding fiber; the film was deposited after removing the cladding of the fiber. The sensor response is very fast even to a slight change in relative humidity and has a good dynamical range. The sensor is quite repeatable and fully reversible. The performance of the sensor was compared against a commercially available relative humidity sensor and was found to be sensitive to RH ranging from 3 to 90%. The sensor developed was found to be faster than the commercially available sensor in the higher humidity range. The time stability of the sensor has also been checked and was found suitable for a long term monitoring application. The sensor should be quite useful for monitoring RH in harsh industrial environments.

In this paper a new quasi-distributed sensor suitable for multi-point detection and localizing of alarm conditions along large structures is presented. The sensor is based on a serial array of equal low-reflective fiber Bragg gratings. The sensor interrogation employs measurement of light intensity at a fixed reference wavelength. Difference between the reference wavelength and the Bragg wavelength in normal conditions set a threshold level for detection. Method was tested experimentally in two different configurations. A simple design of the sensor in combination with the economical interrogation technique makes this sensor interesting for real applications.

As optical fiber sensors take an increasingly important role in structural health evaluation, it is vital that a thorough understanding of the mechanical behavior of these sensors be examined. Previous studies have usually looked at the behavior using uncoated fiber. However this study examines the behavior of both coated and uncoated fibers. A theoretical assessment using a three-dimensional finite element model for both coated and uncoated optical fibers is presented. Results show that the coating stiffness can significantly affect the strain transfer from the member under load to the optical fiber. With a stiff coating (or no coating), the fiber will exhibit maximum sensitivity, but the calibration factor (i.e., the fraction of strain transmitted to the fiber) can be affected by the thickness of the glue. For a soft coating, the calibration factor is not as strongly affected by glue thickness, but the strain sensitivity can be quite low. The three-dimensional finite element model can provide guidelines for the optimized design of strain sensors. In addition, a straightforward analytical solution shows good equivalence with the theoretical solution under certain conditions. Experiments using an interferometer have been conducted to verify the results of the theoretical study and have shown good correspondence.

Continuing research into a novel distributed crack sensor yields quantitative results. Crack monitoring is an important element in making structural health assessments of concrete structures. The current investigation aims to develop a distributed crack sensor that does not require prior knowledge of crack location and employs a small number of fibers to monitor a large number of cracks. The basic design of the sensor is a polymer sheet containing an inclined fiber that is coupled to a structure. The principle of the sensor is that cracking in the structural member leads to cracking in the polymer sheet that induces fiber bending which leads to signal loss. Monitoring the backscattered signal provides crack opening size and location. A theoretical model for optical fiber loss prediction along with experimental results is shown to be in close agreement. Previous reports addressed the feasibility of such a novel sensing technique. This report will show quantitative results, which enhances the credibility of this new sensing method.

The characterization of solid suspensions in fluid is discussed with reference to existing methods used in optics (turbidimetry). Merits and flaws of the present standard for turbidity measurements are discussed. A method for a more profound characterization of solid suspensions in fluid, based on multi-angular scattering measurements, is presented. A simple model for experimental data interpretation is developed. Results of the model are compared with measurements performed on monodisperse particulate.

One of the most serious problems relevant to the use of optical fiber sensors in real-world environments is surface fouling, that is, the cumulative build-up of undesirable material on the working surface of a sensor. This paper present the results of anti-biofouling tests on coated fiber optic probes for reflectance spectroscopy in blood- simulating foul media, namely Bovine Serum Albumin (BSA) and Fibrinogen. The anti-biofouling coating, a proprietary invention of Biocompatibles Ltd., was a cross-linkable Phosphorylcholine (PC) polymer with Silane functionality, to improve adhesion to silica-containing substrates. All tests in BSA and Fibrinogen showed that PC-1036 coating was efficient in avoiding the build-up of biological material. In fact, optical signal variations of un-coated probes showed fluctuations in the 6-20% range, while coated probes exhibited a nearly-stable optical signal. These results were also confirmed by a microscopic check, which showed adhesions of biological material to un-coated probes.

Measurements were performed on gratings glued on different samples made of strips of commercial glass or iron. The samples were heated or cooled inside an oven or a thermo-cryostat. The Bragg wavelength shift was detected by means of an optical spectrum analyzer. The results of measurements made under different experimental conditions will be reported. These show a good linear relation between the temperature variation and the Bragg wavelength shift, but also reveal problems related to the glue hardening or to the partial ungluing of the gratings, depending on the sample material and on the glue used.

We show simulated results about changes of the polarization states from a beam of light in an optical fiber, when we introduce a magnetic field in one section of the fiber. The model includes controllable parameters such as, the current applied to a reel (magnetic field), the birefringence, the incident angle of the light and the magnetic field into the fiber. The theory, simulations and experimental verification of this problem are discussed.

Infrared Spectroscopy has been confirmed as an interesting technique in the process of environmental pollution monitoring. This detection technique is related to the absorption coefficient of each hazardous gaseous compound. When this coefficient is low, as in the case of carbon dioxide, or else, when the gas concentration is small, the transducer has to be designed in order to maximize the interaction between the gaseous compound and the light beam. In addition, the gas cell must be portable, low-size and cost effective. The multipass absorption cell presented in this communication satisfies both requirements, compact physical size and large interaction length. The design is based on a cylindrical cell with a reflective configuration. The dimensions of this cell are carefully adjusted in order to have a completely closed optical path around the contaminant. With this structure, an optical path about 313 cm. could be achieved with a physical size of 20 cm. In this communication, theoretical simulation and preliminary results will be presented to demonstrate the functionality and versatility of the developed gas cell.

Surface plasmon resonance (SPR) affinity sensing, the problem of bulk refractive index (RI) interference in SPR sensing, and a sensor developed to overcome this problem are briefly reviewed. The sensor uses a design based on Texas Instruments' Spreeta SPR sensor to simultaneously measure both bulk and surface RI. The bulk RI measurement is then used to compensate the surface measurement and remove the effects of bulk RI interference. To achieve accurate compensation, robust data analysis and calibration techniques are necessary. Simple linear data analysis techniques derived from measurements of the sensor response were found to provide a versatile, low noise method for extracting measurements of bulk and surface refractive index from the raw sensor data. Automatic calibration using RI gradients was used to correct the linear estimates, enabling the sensor to produce accurate data even when the sensor has a complicated nonlinear response which varies with time. The calibration procedure is described, and the factors influencing calibration accuracy are discussed. Data analysis and calibration principles are illustrated with an experiment in which sucrose and detergent solutions are used to produce changes in bulk and surface RI, respectively.

A new optical integrated refractometer, realizable using standard silicon integrated circuits technologies, for chemical and biochemical sensing applications is presented. The sensor is based on an antiresonant reflecting optical waveguide (ARROW) and uses, as the sensing principle, the strong attenuation dependence on the refractive index of the outer medium. Theoretical predictions and numerical analysis of the sensor behavior are shown along with design trade-offs, sensitivity and measurement range.

This paper focuses mainly on DMT transmission technology applying to downhole image transmission to extend bandwidth, also considers the details about using digital signal processor (DSP) to compress, process and reconfigure the image taken from infrared CCD camera and to process signals from multi-parameter sensors. The system is composed of multi-parameter sensors, infrared camera, TMS320c6x DSP for image compression and reconfiguration, ADSL modem chipset, ground computer, etc., which extends the bandwidth, decreases signal attenuation and abates the noise. Therefore system implements real time downhole imaging, multi-parameter monitoring and inspection by two-wire transmission over 7000 feet no repeaters.

This paper briefly outlines some of the on-going research work in fiber optic sensor technology at the University of Strathclyde. Five principal themes are identified including two in distributed sensing examining liquid detection and mechanical strain detection, a highly multiplexed system for the detection of methane gas and two specialized point measurement systems, one to detect the presence of drugs in the eye and the other to facilitate the non-contact assessment of the mechanical properties of materials. These examples, whilst not exhaustive, represent the cross section of activities on-going at Strathclyde and the diversity of applications within which the group has become involved. The work described here is all current though some has been established for several years. Within it are contributions from several members of the Group and it includes interactions with many external organizations who are acknowledged within the paper.

Design, validation, and implementation of an optical spectroscopic system for high-throughput analysis of combinatorially developed protective organic coatings are reported. Our approach replaces labor-intensive coating evaluation steps with an automated system that rapidly analyzes 8x6 arrays of coating elements that are deposited on a plastic substrate. Each coating element of the library is 10 mm in diameter and 2 to 5 micrometers thick. Performance of coatings is evaluated with respect to their resistance to wear abrasion because this parameter is one of the primary considerations in end-use applications. Upon testing, the organic coatings undergo changes that are impossible to quantitatively predict using existing knowledge. Coatings are abraded using industry-accepted abrasion test methods at single-or multiple-abrasion conditions, followed by high- throughput analysis of abrasion-induced light scatter. The developed automated system is optimized for the analysis of diffusively scattered light that corresponds to 0 to 30% haze. System precision of 0.1 to 2.5% relative standard deviation provides capability for the reliable ranking of coatings performance. While the system was implemented for high-throughput screening of combinatorially developed organic protective coatings for automotive applications, it can be applied to a variety of other applications where materials ranking can be achieved using optical spectroscopic tools.

This paper summarizes our recent activities to develop analytical spectroscopic tools for high-throughput screening (HTS) of combinatorial chemistry libraries and the adaptation of the developed techniques to more traditional, i.e., laboratory and manufacturing, scales. It is shown that, for a broad variety of applications, optical spectroscopic detection methods have a suite of attractive features that make them almost ideal HTS tools. Strategies for the development of new high-throughput screening tools are presented, followed by analysis of requirements for development of multivariate data analysis methods for prediction of properties of combinatorial materials, determination of contributing factors to combinatorial-scale chemical reactions using evolving factor analysis and multivariate curve resolution chemometric methods, high- throughput optimization of process parameters, and applicability of the developed HTS tools for in-line monitoring of scaled-up reactions.

We report a new configuration of the fiber optic voltage sensor based on the Bi₁₂TiO₂₀ crystal, which allows simultaneous measurements of both voltage and temperature. In our scheme, a quarter-wave plate, being an inherent element of voltage sensor, serves simultaneously as a phase-shifting element and as a temperature sensitive element. The sensor operates at two wavelengths (633 nm and 976 nm). The sensor has a linear temperature characteristic within the range of 10divided by70 degree(s)h, providing the accuracy of temperature measurements of 0.3 degree(s)h. As a voltage sensor, this device has a linear amplitude characteristic up to 1000 V_rms and the excellent temperature stability of 0.1 % within the temperature range of 10divided by70 degree(s)h.

The basic Sagnac acoustic sensor array consists of a set of fiber hydrophones placed asymmetrically in a long Sagnac loop. It uses time division multiplexing (TDM) to address individual sensors. A new Sagnac-based array is described that uses a folded loop to reduce acoustic pick-up along the loop. This configuration also enables the use of polarization biasing to provide every sensor in the array with a stable phase bias of arbitrary value (including +/- (pi) /2, for maximum sensitivity), thus eliminating signal fading. A further benefit is the use of balanced detection to eliminate the excess noise from the broadband Er-doped fiber source. These improvements are demonstrated experimentally, as well as a minimum detectable signal close to the shot-noise limit (~0.06 (mu) rad/(root)Hz).