Current trends of fiber optic sensor technology are in a direction of a broadening scope of sensor innovation based on a few basic concepts. Both single-mode and multimode fibers have their proponents: single mode for primarily interferometric sensors and multimode for primarily amplitude-modulated sensors. This paper illustrates four unique and innovative multimode sensor designs and also discusses the basic inhibition to more rapid utilization of optical fiber sensors. A case is made for more effort in standardization of optical fiber sensor interface design and integration requirements. To benefit the optical fiber sensor R & D and small business community, attention to system level requirements is necessary to encourage greater utilization and achieve greater exploitation of the benefits offered by optical fiber sensors.

We have completed development of a temperature compensated, self-referenced, microbend fiber optic pressure transducer for total pressure measurement. This transducer outputs the sum of altitude dependent background pressure and dynamic pressure proportional to air speed. During planned flight tests, the fiber optic pressure transducer will be installed in the same pitot pressure line as the present electronic pressure transducer, so that simultaneous data from the two transducers can be collected for subsequent analysis and comparison. Design information and design trade-offs for fiber optic total pressure measurement are presented in this paper. Methods to make pressure seals to achieve absolute pressure transduction are discussed. Information is provided on microbend fiber optic sensor design and thermal compensation. The approach used for wavelength division self-referencing is described to make the transducer output insensitive to link cable bending and connector mating/demating. Pressure calibration data is presented.

An axial flatted mandrel type of fiber optic hydrophone, named as Mark VI, has been constructed and tested. The sensor is based on a Michelson type interferometer and is built with polarization-maintaining fiber optic components to suppress signal fading due to changes in polarization. The sensitivity is tested in a range from 200 Hz to 1500 Hz. Up to 1000 Hz the sensitivity is found to be 275 mrad/Pa or higher. With 0.8 m of sensing fiber the normalized sensitivity is found to be -277 dB re 1/(mu) Pa, which is one of the highest ever reported. Up to 1000 Hz the noise level of the Mark VI is about 10 dB below Seastate Zero.

An all polarization-maintaining fiber Mach-Zehnder interferometer has been developed for simultaneous measurement of strain or acoustic pressure and temperature. The two forcefully maintained polarization states act as two separate interferometric sensors. In this study, longitudinal strain and heat were applied to the same portion of the fiber to experimentally evaluate cross-sensitivity effects created by simultaneous application. Experimental measurements using a passive homodyne demodulation scheme based on a 3 X 3 coupler agree well with those predicted by a finite element model of the fiber. In addition, response of the interferometer to simultaneous disturbances of acoustic pressure and temperature were calculated. Results of this study show that the cross-sensitivity is negligible and may be ignored for the fiber examined in this study. Furthermore, simultaneous measurement of temperature with another desired measurand has potential to eliminate measurement errors and limitations on resolution that currently limit the use of fiber interferometers in industrial and structural applications.

We present a theoretical and experimental study of a tapered optical fiber-based sensor design that significantly increases optical detection sensitivities for measurement of small mechanical deflections in diaphragm-type fiber optic pressure sensors. By using tapered fibers, we experimentally observed up to eight-fold increases in optical signal modulation levels. We also discuss taper design considerations that maintain system optical power throughput and provide consistent increases in numerical apertures.

We present a novel dual-diaphragm-based, integrated pressure and temperature sensor design for aerospace applications that require accurate, durable, and temperature-compensated pressure sensors. We discuss potential improvement in the sensor's high-temperature capabilities, and demonstrate significant increases in signal-to-noise performance and accuracy, resulting from the dual-diaphragm design. We also describe an integrated optoelectronic transceiver design, employing a dual-wavelength error compensation approach, for pressure and temperature sensing. Other issues leading to practical sensor systems are also discussed.

This paper describes the design and testing of an embedded fiber optic sensor with high sensitivity and broadband response. The sensing principle is based on the observation of stress-induced birefringence in an optical fiber embedded in a flat panel. The sensor was designed to measure low-level stresses in sea ice, however, the sensing principle and measurement techniques presented here have general application for embedded stress and pressure sensors.

LP₀₁-LP₀₂ intermodal interference in highly birefringent (Hi-Bi) elliptical jacket and bow-tie optical fibers was studied experimentally. The response of the interferometer to strain was measured for different polarization inputs. The experiments are shown to agree with a previous theoretical investigation of LP₀₁-LP₀₂ intermodal polarization interference. The modal distributions of the interfering modes are found to be different in elliptical-core and in bow-tie fibers. Comparison with the LP₀₁-LP₁₁ interferometric response is presented. Optimum detection schemes are suggested to extract maximum information from the strain-modulated sensor signal.

With two birefringent optical fibers in series, it is possible to obtain a sensor for measuring angular positions. The resolution is better than 0.1 degree(s). This method eliminates all errors due to possible fluctuations of the power emitted by the source, as well as those due to variations of the fiber's birefringence in the range of temperatures between 0 degree(s) and 100 degree(s)C.

Channeled spectrum of an optical beam generated by a diode laser below threshold after traversing a two-beam interferometer is spectrally analyzed using a grating and a CCD linear array. The paper focuses attention to the Michelson interferometer for displacement sensing. Some particularities and results are presented for the case when the same technique has been applied for determining the widths of parallel sheets of transparent materials or the index of refraction of some liquids. With the present technique, displacement in the range 20 micrometers to 3.5 mm and index of refraction for some liquids were measured with less than 1% error. An analysis of the experimental error sources is made which shows that the ultimate accuracy may be considerably increased.

The Alcatel SEL single-axis fiber-optic gyros are described. Application areas are identified and rationale is given for the use of fiber-optic gyros in the different market segments. The applications reach from retrofit of mechanical rate gyros to integrated navigation systems. The ongoing development and engineering effort is concentrating on multiple-axes solutions with reduced size and optimized manufacturing cost. The most promising subsystem is a tactical grade inertial measurement unit with a fiber-optic gyro triad as rotation rate sensors.

Sources with broadband spectra are required for high-grade fiber optic gyroscopes (FOG). To date, the most widely used broadband FOG source is the superluminescent laser diode (SLD), which was developed by the semiconductor laser industry to meet this specific market. However, in spite of significant improvements, commercial SLDs still suffer from a few shortcomings. In response to these limitations, a second class of broadband sources has been under investigation over the last few years, which utilize a rare earth doped fiber as the active medium. Several types of broadband fiber sources have been demonstrated. They offer the advantages of high efficiencies, pumping with a laser diode (LD), high power into the FOG (tens of mW), and a mean wavelength stability with temperature at least one order of magnitude greater than for an SLD. Several university and industrial laboratories have now produced broadband fiber sources with properties far exceeding, on all counts, those of SLDs. The object of this paper is to review the properties of these sources, and their preliminary performance in FOG test beds.

A parametric study has been performed on fiber gyroscope sensing coils to investigate the effects of substantially reducing the inner diameter. Three coils with inner diameters ranging from 6.0 to 1.5 cm were precision-wound with 350 meters of a high-strength, bend-insensitive single mode fiber typically used in Fiber Optic Guided Missile payout systems. Optical loss and extinction ratio measurements were made on the test coils over temperature. The results indicate that the optical loss in the bend-insensitive fiber is not significantly affected by reducing the coil diameter. The fluctuation observed in optical loss during the first thermal cycle is significantly reduced. Extinction ratio data support the theory that the bending-induced birefringence can be significant in single mode fiber wound onto small coils.

We have developed a fiber optic gyroscope (FOG) using a single mode fiber (SMF) coil and integrated optics (IO), with intermediate-grade performance (bias stability: 3 degrees/hour 1 (sigma) ). Conventional FOGs, which require higher performance than intermediate grade, need polarization maintaining fiber (PMF), an obstacle to cost reduction because of expense. Our unique technique using depolarized light has made it possible to replace the PMF coil with SMF coil, thus reducing cost. This paper describes the FOG configuration we adopted and the test results of our product models that applied this technique under practical environments (temperature, vibration, and magnetic field). We compare the test results of the products using PMF coil.

Fiber optic gyroscopes (FOGs) have been developed for vehicle navigation systems and are used in Toyota Motor Corporation models Mark II, Chaser and Cresta in Japan. Use of FOGs in these systems requires high reliability under a wide range of conditions, especially in a temperature range between -40 and 85 degree(s)C. In addition, a high cost-performance ratio is needed. We have developed optical and electrical systems that are inexpensive and can perform well. They are ready to be mass-produced. FOGs have already been installed in luxury automobiles, and will soon be included in more basic vehicles. We have developed more inexpensive FOGs for this purpose.

The paper discusses the range of applications for interferometric fiber optic gyroscopes IFOGs in space inertial reference units (IRUs) with an emphasis on satellite usage. The requirements for space IRUs are discussed along with the corresponding features that give IFOGs a singular advantage for many space IRU applications. Development of Honeywell's high performance closed-loop IFOG IRU product is described. Radiation tolerance is a key challenge in many space applications. Accordingly, another possibility for achieving high radiation tolerance using a depolarized IFOG (D-IFOG) is given. Test results for the high performance IFOG for space IRUs is presented as well as open-loop D-IFOG test results.

Northrop's Electronics System Division has built and tested a tactical fiber optic gyro (FOG) with all-digital signal processing. The Northrop FOG uses 160 meters of polarization maintaining optical fiber wound on a spool 29 mm in diameter. Without any data compensation, this FOG has demonstrated excellent scale factor stability and non-linearity (< 100 ppm) over a high dynamic range (+/- 1400 degree(s)/s), low random walk (< 0.02 degree(s)/(root)hr), and outstanding bias stability over temperature and day-to-day (< 1 degree(s)/hr). An inertial measurement unit (IMU) utilizing a FOG/MSA (Micro Silicon Accelerometer) cluster has been developed and integrated with a GPS receiver. Testing was done to demonstrate performance of the sensor and IMU over the military environment.

A fiber Brillouin ring laser gyro composed of single-polarization single-mode fiber is analyzed. The eigenstate of polarization both for the pump light and the stimulated Brillouin scattering (SBS) in the fiber ring-resonator is strictly considered. It is clarified that this structure ensures stable and efficient pump, which makes possible stable lasing of the SBS with low threshold. The relation between the temperature and the behavior of the SBS lasing is also discussed.

Corning has introduced a new polarization-maintaining optical fiber to satisfy customer requirements for a range of commercial and military FOG applications. This fiber has an elliptical core, matched-clad design, and is intended for operation in the 780 to 850 nm wavelength region. The fiber has a beat length less than 1.5 mm, attenuation rate less than 10 dB/km, and a typical coiled h-parameter less than 1.5 X 10^-4 m^-1 in the designated operating wavelength range. It has a cladding diameter of 80 micrometers and a coating diameter of 185 micrometers . The coating is an acrylate system, similar to that used in telecommunications optical fibers. We report on the performance of this elliptical core fiber for a variety of environmental exposures representative of an automotive application.

A novel configuration for an all-fiber ring resonator gyroscope utilizing a double cavity and a short-coherence-length light source is presented here. The gyroscope can achieve a higher finesse than a Sagnac interferometer resulting in higher sensitivity as a result of multiple path interferences. The sensitivity can be increased further by the insertion of an optical amplifier which compensates for attenuation in the fiber ring. The proposed instrument makes use of fewer components than other low-coherence-length, high-finesse gyroscopes based on a combination of the Sagnac interferometer and ring resonator. Simple phase-tracking techniques can be used to determine the rotation rate. A light-emitting diode is used as light source in order to reduce noise that results from coherent Rayleigh back scattering, the Kerr effect, and dc phase bias shifts. The proposed gyroscope can be made polarization insensitive by employing a Faraday rotator mirror.

A novel fiber resonator configuration is proposed to reduce the drift due to polarization fluctuation for a cheap resonator fiber optic gyro (R-FOG) having medium grade performance. The resonator can be made of an ordinary single mode fiber. Influence of drift sources has been considered, and it is confirmed that the configuration shows medium grade performance.

We have investigated fiber optic gyroscopes that use phase-modulation signal processing for use in automobiles. These gyroscopes use an integrated optical gyrochip and low-cost elliptical-core polarization-maintaining optical fiber. Fiber-to-fiber insertion loss deviation is less than +/- 0.4 dB at a wavelength of 0.83 micrometers over a temperature range of -30 to +80 degree(s)C, while the core dimensions of pigtailed fiber are as small as 4 X 1 micrometers ². A gyroscope was developed for navigation systems and on board testing is now being performed. A gyroscope for chassis control systems is also being developed.

We have developed two kinds of fiber optic gyro prototypes, an all-fiber gyro and an optic integrated gyro, which will be used for AHRS. The dimension of a typical gyro is (Phi) 75 mm X 25 mm with 200 m PM fiber. By means of the phase traced technique, the dynamic range is over +/- 500 degree(s)/s with 10^-3 - 10^-4 scale factor linearity. The gyro's noise equivalent to rate is 0.5 degree(s)/h - 1 degree(s)/h (1 (sigma) ). In order to study some characteristic which is relative to the state of polarization (SOP), we used the Jones matrix to establish a model of SOP of FOG, in which the fiber loop is represented by a `two-way linear phase delayer.' As a result of deduction, the output signal of FOG is a function of the delay value and direction of birefringence axes of the fiber. If we send the depolarized light into the fiber loop, the output intensity will be independent of the phase delay and direction of optic axes. By using the model of SOP, we also deduced that the depolarization is conditioned by cos(2 (beta) ) equals 0, where (beta) is an angle of birefringence axes between two fibers in a depolarizer.

We describe a digital integrating fiber-optic gyroscope with a microprocessor-based phase tracker, using an open-loop configuration. The Sagnac phase shift is electrically compensated by a phase generated in the microprocessor-based system. Different from analog schemes, this phase tracker is based on software generation of sine- and cosine-dependent compensating functions that are deduced from integrated interferometric output of gyroscope using dynamic phase modulation. Computer simulation has shown that this scheme may provide wide- dynamic-range sensing with an open loop fiber gyroscope. Potentially a group of fiber optic gyroscopes with such a phase tracker may be interfaced directly to navigation systems.

One of the more successful multimode fiber optic sensors to data has been the Faraday sensor. This type of device has been used to detect rotational speed, torque, proximity and other parameters. When in a reflective configuration, the transducer element has consisted of a thin Faraday film between a polarizer and a mirror. In this paper, it is shown that enhanced performance of the sensor results when the polarizing element is removed from the transducer. A theoretical analysis is presented along with supporting experimental results.

A new topology for an openable Faraday current sensor is presented with a demonstrated resolution of 7.2 mA/(root)Hz over a measurement range from 1 to 1500 Amp. The sensitivity of the system was 2.21 X 10^-5 rad/A. Since this sensor is fabricated in an `openable' form emulating a conventional current clamp, it can be used either in permanent installations or for short term diagnostic studies.

A wavelength-insensitive fiber optic sensor configuration is presented. It is based on two variable ratio couplers in series, the one acting as a reference while the other acts as the sensing element. Difference-over-sum processing yields linear outputs for the reference and sensor which are insensitive to fluctuations in optical intensity. By subtracting the reference from the sensor output wavelength compensation is achieved. The characteristic behavior of this sensor was determined experimentally and the results compared to computer simulations which were based on a theoretical model. Theoretical and experimental results show good agreement. The compensation technique is suitable for any variable ratio coupler sensor and is not limited to axially strained fused tapered couplers.

An intrinsic refractive index sensor has been developed based on Fresnel reflection at the interface between the single mode fiber core and a cap material. The sensor is capable of measuring the refractive index of the cap material and can be applied to temperature, pressure, and magnetic and electric field sensing. Suitable cap materials may be chosen which have a birefringent response to mechanical stress, thermal stress, electric fields, or magnetic fields. A temperature sensor application characterizes the technique using cap materials of carbon tetrachloride, toluene, and dodecane.

We used beam propagation methods to numerically simulate straight and short-bend optical fiber sensors. The methods are specifically applied to polymer jacket optical fiber temperature sensors and our results show the main features presented by the experimental data.

We report on a prototype of an all-fiber optical accelerometer based on a compliant cylinder design. The measured performance is close to the requirements typical for seismic applications. The operation of the sensor is stable in a temperature range from 20 degree(s)C up to 80 degree(s)C. Considerations towards the development of a high temperature version are described.

A detailed design study is presented as a guide in the design of fiber-optic-based Fabry-Perot type interferometric sensors using low-coherence signal recovery. Several configurations using Michelson and Fabry-Perot type interferometers as the local receiving interferometer for transmissive and reflective type Fabry-Perot sensing interferometers have been investigated. Optimum design parameters are recommended for the use of the different configurations.

A novel fiber sensor based on the interference of the exact constituent modes of the LP₁₁ fiber mode of a solitary standard-communication-grade optical fiber is demonstrated. The coupling of the constituent modes due to birefringence is shown to produce a linear rotation of the lobes at the fiber output. A novel passive demodulation scheme is used to produce signals in quadrature. A simple demonstration of its application to torsional vibration is presented.

Three different theoretical models of modal power distribution in multimode fibers are developed, including a sophisticated wave optics model. All three are tested against experiment. Also, the far-field light distribution from a multimode fiber is considered; far- field chromaticity distributions are calculated and far-field and near field intensities are compared.

Hydrostatic pressure and uniaxial longitudinal strain effects in twisted highly birefringent optical fibers have been investigated from the point of the Marcuse mode-coupling theory. The problem is analyzed in terms of local normal modes of the ideal fiber and in the limit of weak twist, where large linear birefringence dominates over twist effect, and therefore twist coupling between local modes is not effective. The authors present the results of birefringence measurements in highly birefringent bow-tie fibers influenced simultaneously by hydrostatic pressure up to 100 MPa and twisting the result for highly birefringent elliptical-core fibers influenced by uniaxial longitudinal strain up to 4000 (mu) (epsilon) and twisting effect. The birefringence measurement method is based on twist-induced effects and has been successfully applied in a stress environment. The experiment was conducted with a specially designed stress generating device that makes it possible to simultaneously generate various mechanical perturbations such as hydrostatic and radial pressure, axial strain and twist, allowing study of their influence on mode propagation in optical fibers. A comparison with theoretical results as well as with pervious experimental data on stress influence on the beat length parameter in highly birefringent fibers is also provided.

A fiber optic electrometer with oscillating element is described in this paper. The non-contact interferometric interrogation system of electrometer provides high-sensitivity measurement of voltage and charge, inducing very small disturbances in the measured object. The sensitivity of 2 (DOT) 10^-4 V/(Hz)^1/2 was achieved, while the sensitivity of 3 (mu) V/(Hz)^1/2 is predicted from the thermal fluctuation limit. An order of magnitude estimation indicates that the sensitivity to an electric charge close to the electron charge may be achieved with an electrometer of considered type.

We describe the physical principles involved in constructing distributed and remote fiber-optic sensors for vibration and displacement registration on the basis of interferometry and speckle- interferometry methods. Experimental models of such sensors were made and tested. The results show a good coincidence with theoretical predictions.

The special graded index separate-confinement heterojunction multi-quantum well GaAs/GaAlAs lasers are used simultaneously as optical resources, receivers, and mixers for measuring the velocity and distance of an object by the technique of heterodyne.

The automatic testing device for laser rangefinders is one means to check the operating condition and diagnose trouble in laser rangefinders. It is able to both check functions alone, diagnose trouble and be connected with an outer computer network. When no laser is emitted, it simulates laser ranging procedures. By microcomputer supervising, diagnosed trouble can be coded and directly displayed on the five-digit display with measured range data and range errors, or figures can be printed out by a printer.

A fiber-optic temperature sensor has been fabricated by first sputtering a silicon film onto the end of an optical fiber. The approximately one-micrometer thick silicon film serves as a Fabry-Perot etalon whose resonant wavelengths change as a function of temperature. The silicon film is annealed in order to stabilize its structure. This will provide a sensor with acceptable long term stability. The use of wavelength encoding fiber optic sensors provides a high degree of immunity from cable and connector effects. The benefits of this technology include reduced volume and weight, reduced cost, and improved reliability.

We have fabricated a new type of dual-core fiber with two cores, one of which is made of silica and the other of which is made of a liquid with a higher refractive index than silica injected into a cylindrical cavity with a certain length in a single mode fiber. Thus, we have found a feasibility of a new type of temperature sensor in which the dependence of the refractive index of this liquid on temperature is combined with the optical coupling phenomenon in the conventional dual-core fiber. This paper reports our theoretical and experimental examinations on the feasibility of a dual-core silica fiber with a liquid core as temperature sensors.

This report details the development and testing of a thermographic-phosphor-based fiber-optic temperature sensor. The sensor is constructed by removing a region of the fiber jacket and cladding, then coating the exposed core with yttrium oxysulfide doped with a europium activator (Y₂O₂S:Eu). When photoexcited, the europium in the host lattice emits a sharp-line fluorescence spectrum that is characteristic of the temperature of the host crystal lattice. By measuring fluorescence lifetimes, we can deduce the temperature of an optical fiber that is in thermal contact with the fiber. Two different distributions of Y₂O₂S:Eu in the cladding region were evaluated with regard to light coupling efficiency. Theoretical waveguide calculations indicate that a thin core/cladding boundary distribution of Y₂O₂S:Eu couples light more efficiently into the cores guided modes than does a bulk distribution of phosphor in the cladding. The sensor tests showed reproducible response from 20 to 180 degrees Celsius. This technique has several advantages over other fiber optic temperature sensing techniques.

We describe a theoretical and experimental study of an intensity-based, dual-wavelength referenced fiber optic temperature sensor utilizing temperature-induced spectral shifts of optical thin-film interference coatings, deposited on a sensor fiber end. We present coating design considerations that lead to significant increase in transition region spectral shifts and coating-reflected signal modulations, for sensitive temperature measurement. Experimental results demonstrate that high density coating-based sensors provide consistent and repeatable temperature sensing, while low density coating-based sensors experience significant and inconsistent spectral variations and degradation under temperature cycling.

The fluorescent decay time of Cr:YAG single crystals has been determined from room temperature to 300 degree(s)C in order to develop optical-fiber temperature sensors. The sensing crystal was placed at the common end of a bifurcated optical fiber with the two legs connected to the excitation source and to the photodetector, respectively. A 636-nm laser diode pulsed excitation was used to stimulate the emission of the sensitive material and the observed decay was related to the fluorescent lifetime. The absolute fluorescence lifetime was estimated by means of an exponential-decay model, which included baseline offset and noise, to within 0.2%. The calibration and estimation processes were repeated with four different Cr:YAG crystals in order to evaluate the intrinsic repeatability of the material in view of realizing a multi-probe optical-fiber thermometer with full sensor interchangeability. A two- level kinetic model was applied in order to derive the decay-time-versus-temperature curve. The results show that this model fits the experimental data with a standard error of the estimate of 1.6 microsecond(s) , that is comparable with experimental uncertainty. As a consequence of the modeling results we predict that, with the described technique, the upper temperature limit of a single probe can be extended to 400 degree(s)C with a measurement error to within +/- 1 degree(s)C.

A method of using aluminum tube wounded by single-mode fiber as a temperature sensor is proposed in this paper. The optical source of this temperature sensing system is a 2-frequency He-Ne laser. When the temperature of fiber on aluminum is changed, a phase shift in optical signal appears. By using electronic circuits, this phase shift can be detected and compared with a reference signal obtained directly from the laser source. Then one will be able to get the information on temperature according to the difference of phases between these two signals. Two experiments have been performed in the laboratory. In the first experiment the aluminum tube is 12 cm in diameter, 8 cm in height, and 2 mm in thickness, with a fiber length about 60 m wounded 155 turns. The sensitivity is 2.1 X 10^-2 rad/ degree(s)C-m. In the second experiment, the tube is 7.5 cm in diameter and height, and 2 mm in thickness, with a fiber about 10 m length wounded in 21 turns. The sensitivity is 4.9 X 10^-2 rad/ degree(s)C-m. The temperature from 5 degree(s)C to 80 degree(s)C are measured with this design.

The temperature distributions for some hot gaseous systems are axially symmetrical. Examples include the air convected about a heated point or cylindrical source and gas discharges contained in cylindrical tubes. Such temperature distributions may be determined using an integrated optical fiber sensing technique, in which the fiber of one arm of an optical fiber interferometer passes along a chord of the hot gas system, and the measured phase shift provides an integrated temperature along the chord. By repeating this measurement for chord positions throughout the axially symmetrical temperature distribution, and carrying out an Abel transformation of the resultant data, a radial temperature profile can be determined. The integrated optical fiber sensing technique has been applied to the convected air flow above a small volume source of heat. The radial temperature profiles measured using the integrating sensor were compared with profiles obtained using an optical fiber probe sensor, a thermocouple and an unbound laser interferometer. The results reveal many advantages for the integrated optical fiber sensor in respect of precision, resolution and convenience of use.

Among the various fiber-optic sensors, sensors based on interference technique have the highest sensitivity. However, the range of temperature measurement is limited by their periodic natures. The purpose of this research is to improve this situation, and still keep their high sensitivities. We use two interferometers with slightly different sensitivities simultaneously, and the relative phase differences between two fundamental modes in the fibers are measured to determine the temperature. The purpose of extending measurable temperature range is achieved by combining the output signals of those two interferometers.

Temperature dependence of the coupling characteristics between a single-mode fiber and thin film directional coupler is studied. Matching condition of the propagation constants of the fiber half-coupler and thin film waveguide required for maximum power coupling into the thin film guide is investigated. A relation of the coupled power with the change in temperature of the coupler is developed and the temperature sensitivity of the coupled power is compared for both uniform and tapered coupling structures. Experimental results of temperature dependent coupling between the fiber half-coupler and uniform thin film PMMA waveguides of different molecular weights are verified with the theoretical estimates.

An optical fiber pyrometer prototype for accurate measurement of over-heating gas temperature has been developed in this paper. The paper describes the development of novel optical fiber pyrometer and its technique, which could have the potential of measuring temperatures up to 2000 degree(s)C. The working principle of the pyrometer is based on Plarck's Law. The test results are presented.

A fiber-optic temperature sensor based on two U-shape bimetal chips transfer device is introduced in this paper. Twin receiving fiber method is used in the transducer design. The fiber-optic sensor is very simple, highly reliable, and easy to manufacture at low cost. The most outstanding feature of this sensor is that the sensitivity can be adjusted conveniently and the influence of the light source fluctuation on the sensor's measurement is overcome.

A new kind of fiber optic high-temperature sensor for molten metal is presented in this paper. It is composed of a hollow tube and an optic fiber. When the bottom part of the sensor is inserted to the molten metal, the optical fiber receives and transmits the radiation powers emitting from the molten metal surface. Then the temperature of the surface is measured by a double-color pyrometer, based on the assumption that emissivities in used wave band approach each other by using the hollow tube. Regardless of the surface emissivity approaching black body or not, the results of approximating gray body when the sensor is inserted into the molten metal obviated the effect of the uncertain emissivity on temperature measurement.

In this paper, the possible survey of a high-pressure field by using dual core fiber sensors and a differentiator electric bridge is described. Also, the interaction between high-pressure field and a dual core fiber nonlinear coupler is discussed, using the analyzed theory. We have obtained the formula of the theory and some correlative experimental results. We can measure high-pressure (2.2 * 10⁶ V) by using dual core fiber sensors and a differentiator bridge.

Litton is developing an interferometric fiber optic gyroscope for future navigation, guidance, and stabilization applications. The gyro is presently less than three inches in diameter, which is size competitive with current ring laser gyros of equal performance. In this paper we report on the bias, scale factor, and input axis alignment performance of the inertial navigation fiber optic gyroscope over extended, dynamic temperature environments.

We report the construction and performance of several prototypes of a low-cost 3-axis fiber gyro using an electronic phase tracking scheme to provide a post-sensing closed loop operation. These gyros exhibit an output nonlinearity of < 0.1% in our rate tests from 0 to 200 deg/sec, a noise level < 10 deg/hr in a 1 Hz bandwidth, and a thermal dependence of the bias offset approaching 1 (deg/hr)/deg C.

The use of nonlinear strain transduction techniques with fiber Bragg grating sensor elements is reported. Configurations for displacement and magnetic field sensing are discussed, and techniques to allow the multiplexing of a number of devices along a single fiber path are described.

There are two possible topologies to fabricate fiber optic resonators which contain a single, low-loss coupler. The first resonators reported in the literature were of the spliceless design and required a high splitting ratio coupler; they are denoted as a cross-coupled fiber resonator (CFR). The development of low-loss splicing technology enabled rings to be constructed from low splitting ratio couplers, which have been referred to as direct coupled resonators (DFR) in the literature. In this paper, DFR and CFR are theoretically compared, using a matrix formalism implemented in Mathematica^TM. Effects of a non optimum splitting ratio, differential normal mode losses, polarization cross-coupling, and backscatter are examined. An optimum RFOG topology is suggested by this analysis.

We use a polarization maintaining fiber optic gyroscope as a sensor for highly stable and sensitive measurements of fluid flow rates and magnetic fields.

This paper presents an extrinsic Mach-Zehnder type accelerometer that utilizes a gap between a fiber cantilever and a fixed fiber. The problem of light insertion to the single mode fiber across the gap is eased with the use of quarter pitch GRIN lenses. Phase feedback is done through the laser diode in conjunction with active homodyne demodulation. The accelerometer has a dynamic range of 84 dB and a resolution of 10^-4 g. The configuration uses all-fiber components that are readily transferable to the integrated optic domain.

A miniature Fabry-Perot cavity consists of a 10 micron deep by 5 micron wide slit which is formed in a silica (SiO₂) waveguide over silicon with the use of reactive ion etching. The multiple beam interference is due to successive reflections from both walls of the slit. The reflectance close to the critical angle exhibits a Finesse over 20. A model is developed to simulate the loss due to scattering from the etched wall roughness. The loss in amplitude is only 7% after each reflection. Thus, the etched walls are vertical and smooth and can be used as efficient mirrors in integrated-optical circuits and interferometers.

A novel sensor technique using a magnetic thin film as the sensing element and the magneto- optic Kerr effect as the optical read technique has been tested experimentally through magnetic field measurements. Sensitivity results obtained using a simple free space ellipsometry measurement system show a magnetic field sensitivity near 10^-3 Oe at low frequencies. Calculations indicate that sensitivities of order 10^-6 Oe are possible with improvements in the optical system and the magnetic film sensing element. This technique appears to be implementable in a small fiber optic-compatible device, with foreseen advantages including a very high bandwidth, good thermal stability, and the use of a single optical path.

Bend enhanced fiber (BEF) sensors are curvature-measuring optical analogs of elongation- measuring resistance strain gauges. They are made by treating optical fibers to have an optically absorptive zone along a thin axial stripe a few millimeters long. Light transmission through the fiber past this zone then becomes a robust function of curvature, three orders of magnitude more sensitive to bending than in the untreated fiber. Directionality and polarity of curvature are preserved in the light transmission function, over a linear range covering five orders of magnitude, centered about zero curvature. This paper describes a project in which BEF sensors were used to improve teleoperation of a small mobile robot, by instrumenting joint angles, an extension, and four forces. The operator, who formerly had only a televised view from a camera on the robot, now has additional information on a computer screen showing these parameters in graphical form. This information, provided entirely from fiber optic sensors, makes it considerably easier to manipulate the robot. The project also included demonstrations of a multiplexing system for larger BEF arrays, use of BEF sensors in prosthetics, and plasma enhanced chemical vapor deposition of a light absorptive coating on BEF sensors.