An array of eight fiber optic vector magnetometers was designed and constructed for use in undersea applications such as harbors, ports, and waterways. We describe the design and performance characteristics of the array including the single-mode fiber optic system and magnetostrictive transducers. Data is presented from both laboratory measurements and from actual undersea operation.

A magnetostrictive fiber optic interferometric sensor that detects low-intensity magnetic fields has been realized. The sensor is fabricated with 850-nm, single-mode fiber optic cable and couplers configured in a Mach-Zehnder interferometric arrangements. Four sensing arm configurations were fabricated where the magnetostrictive material was geometrically coupled to the fiber optic cable as a: ribbon, cylinder, sandwich, and sputter-coated sheath. The four classes of sensing arms were evaluated using Metglas^TM, nickel, and a combination of Metglas^TM and nickel. Optimization techniques were applied to maximize the sensor's sensitivity. These techniques included: annealing the magnetostrictive material, operating the magnetic field over a range of frequencies, applying a DC bias current to the Helmholtz coil's AC current component, and fabricating sensing arms with polarization maintaining fiber optic cable. The measurements employing the various sensor arm classes revealed that the lowest detectable magnetic flux density was 0.3 mG. This result was achieved using a Metglas^TM ribbon-fiber optic cable configuration where the ribbon's magnetization direction was aligned perpendicularly with the applied 52 kHz AC magnetic field that had a 5- volt DC bias. When operating this configuration with a 10 Hz AC magnetic field that had a 5- volt DC bias, the lowest magnetic flux density that could be detected was 8.9 mG.

Optical current sensors using the Faraday effect promise significant advantages over conventional current transformers. One of the remaining problems is the temperature dependence of the optical current measurement mainly caused by intrinsic or stress induced linear birefringence. By an appropriate annealing process most of the linear birefringence in a fiber coil can be removed. But still a significant temperature drift remains. For AC measurements we have developed a novel compensation method, which uses the DC part of the output signal to compensate the temperature drift. We have achieved a reduction in temperature sensitivity by a factor of 8 to about 0.5% over a temperature range from room temperature to 80 degree(s)C. The overall accuracy of the current sensor is now limited only by the system's noise and stability.

A new type of Faraday effect current sensor consisting of a single SF57 glass block having dielectric multilayer mirrors coated to have polarization-preserving perfect resolution and containing no parasitic field sensitive parts is developed. A good isolation from the external current and field is demonstrated.

Recent research at NIST has greatly extended the capabilities of Faraday effect sensors for both magnetic field and electric current measurements. Current sensors using single-mode optical fiber show temperature stability near material limits, and are approaching commercial availability for application in the power industry. The Faraday effect in iron garnets shows great promise for measuring current at low levels and/or high speeds. Sensors with noise equivalent currents of about 200 nA/(root)Hz have been demonstrated. Magnetic field sensors using iron garnets and flux concentration, have led to sensors with noise equivalent magnetic fields in the range of 1 pT/(root)Hz.

A technique for simultaneous measurement of temperature and magnetic field is presented. Absolute temperature is recovered using a `white light' source combined with a tandem interferometer configuration. Magnetic field is recovered from the modulation of interferometer fringes when the sensor is illuminated with a single frequency source. The broad-band and narrow-band inputs are multiplexed into the sensor by modulating the injection current of a single laser diode source from just below threshold to near maximum operating current. In this technique the temperature is measured over exactly the same optical path as that subject to the magnetic field.

Various metallic glass ribbons made of Co₇₀Fe₁₀B₂₀, Co₇₆Fe₄B₂₀, Co₈₀B₂₀ and Ni are developed using the melt-spinning technique and their magnetic properties, affecting the performance of a typical interferometric optical fiber magnetic field sensor, are tested. By bonding the metallic ribbons to a single mode fiber arm, a typical interferometric fiber optic magnetic field sensing system is constructed. The ac magnetostrictive responses for the metallic glasses measured with the fiber optic sensing system show that the dc bias field for the maximum response with a Co₇₀Fe₁₀B₂₀ ribbon is approximately 0.97 Oe and that with a Ni ribbon is 23 Oe. The Co₇₀Fe₁₀B₂₀- and Ni-transducer exhibit maximum magnetostriction near 0.5 kHz while the Co₇₆Fe₄B₂₀ transducer demonstrates peak response at 0.9 kHz AND 12 kHz. The measured effective magnetostrictive parameters and saturation magnetostrictions are 2 X 10^-7/Oe² approximately 3 X 10^-7/Oe² and -4.6 X 10^-6 approximately 5.7 X 10^-6, respectively. Typical optical fiber sensors exhibit minimum detectable fields of the order of approximately 10^-5 Oe(rms)/(root)Hz.

The expansion of the high voltage power transmission system since the 50s and 60s has aroused an interest in using optical techniques for measuring the electric current. As the most promising method among them, a current measuring method which uses a magneto-optic effect called the Faraday effect have been proposed. In principle, this method is excellent in such aspects as control of electromagnetic induction noise, rationalization of electrical insulation, extension of dynamic ranges and frequency bands. The authors have developed an optical current transducer based on the Faraday effect of dense flint glass for the purpose of utilization in 110 KV substation. It uses the rotation of the plane of polarization by a magnetic field exhibited in certain glasses. As a result of the development, high accurate optical current transduce such as the ratio error +/- 0.2% when compared to the reference CT and temperature stability (from -20 degree(s)C approximately +40 degree(s)C) +/- 0.5% were obtained. Furthermore, short-circuit current (11 KA_peak) was measured with the optical current transducer, and the accuracy was +/- 3%, the bandwidth was approximately 2.5 KHz. This paper describes the principles, structures, operations, and testing results of the optical current transducer.

This paper will present a brief overview of the current activities in fiber optic distributed, integrating and quasi distributed measurements within the University. The research focuses on applications in structural monitoring and includes a distributed moisture ingress monitor and some simple systems exploiting special cable structures to implement specialized strain and distance measurement for self surveying structures.

We report here progress on a NASA program to develop fiber optic interferometric sensors for aeroacoustic measurements. As reported earlier, NASA's first fiber-optic microphone was developed and fabricated. Preliminary anechoic chamber tests demonstrated successfully its feasibility as an aeroacoustic sensor. Improved performance of a newly designed sensor head is presented here in terms of frequency response function and noise floor.

This paper reviews the development progress of fiber optic interferometric acoustic sensors at OPTIPHASE, INC. The primary development objective is to evolve fiber optic interferometric sensor technologies which are cost compatible in their respective application methods. This mandates that only low cost approaches be considered. The sensor technology chosen involves extrinsic Fabry Perot devices configured as low finesse sensors which are compatible with low-cost dual wavelength interferometric demodulation techniques (also developed by OPTIPHASE). This paper addresses both single element and multi-element sensor systems.

We have developed a technique for distance measurement in which the spectrum from a sensing interferometer is monitored directly with the aid of a diffraction grating and a linear charge-coupled device (CCD) array. The method described is a form of white light interferometry whereby a diffraction grating disperses the composite frequencies which are then examined by a CCD array. This paper presents the experimental results obtained for a fiber Fabry-Perot version of the sensing interferometer, using a powerful pigtailed super luminescent diode. Presented also are the processing techniques used to recover the displacement. The techniques are based upon a software package designed to derive the signal frequency of the channeled spectra. The results are compared with those obtained using previously described signal processing methods. Methods of calibration are explored using reference cavities of sub-micron accuracy to allow absolute measurement.

Fiber lasers formed with rare earth doped fiber and fiber grating reflectors are being developed as tunable single frequency devices for a number of communications applications. These devices can also be used as sensors, and can be multiplexed using the inherent wavelength encoded nature of their output. Fiber Bragg grating based laser sensors can be implemented in configurations suitable for monitoring weak dynamic or quasi-static strains, and are thus useful for a range of sensing applications. This paper will review some work in this area.

A review of the Fiber Optic Control System Integration program is presented relative to its degree of fiber optic sensor integration. The evolutionary stage of this integration is discussed in conjunction with the current day notion that fiber sensors have failed to proliferate as rapidly as anticipated ten to fifteen years ago. Several signs of hope and progress are noted.

Smoke detectors in general, are usually threshold devices that frequently experience false alarms. Optical smoke detectors usually depend on the measurement of optical power absorption and scattering across an air gap and are usually threshold devices. Fiber optic sensor technology offers potential improvements for existing smoke detector technology. We have developed a new smoke sensor design based on wavelength selective absorption and scattering that generates a continuous measurement of smoke density. This technique provides first order compensation for water and dirt coatings on the optical surfaces and for optical power and ambient light changes. The sensor has a 2 inch sensing region and utilizes multimode technology with an 850 nanometer LED source. Experimental models of the fiber optic smoke sensors were tested successfully in our laboratory and on the ex-USS SHADWELL. Operational performance advantages of the fiber optic smoke sensor are expected in the areas of monitoring visibility, reducing false alarms, improving reliability, and continuous measurement of smoke density; this will improve fire detection capability and will assist in developing fire fighting strategy. Application of the sensors are planned for the shipboard environment to provide sensor input to new damage control management systems.

The accurate measurement of growth parameters is essential for the development of automated, low cost silicon growth technology. The ideal growth parameter sensor for these applications is accurate, non-invasive, immune to electromagnetic interference (especially if induction heaters are used), and able to function at high temperatures. Fiber optics sensors exhibit characteristics which can meet these requirements. In this paper we report on the first use of optical low-coherence reflectometry (OLCR) for on-line, non-invasive characterization of edge-defined film-fed growth (EFG) solar silicon sheets during the actual silicon growth process. This OLCR sensor system has been used to measure vertical profiles of the thickness and flatness of one side of an EfG grown silicon octagon to an accuracy of +/- 5 micrometers . Since thickness and flatness are two important growth parameters for sheet grown silicon, the use of this non-invasive sensor for on-line silicon sheet growth monitoring may lead to improvements in solar cell manufacturing processes. In addition, this technique shows promise for providing non-invasive dimensional monitoring for a variety of other crystal types during the crystal growth process.

In this paper, several kinds of bi-frequency interferometers in measuring micro-vibration are discussed. Their principles and light paths are analyzed and presented. The experimental methods and measuring results are given.

We describe our activity on interferometric fiber-optic gyroscope (I-FOG) technology: recent results on our improved large-operating-range prototypes (FOG 50); development on three- axis clusters using a single source; work on high-performance I-FOGs (FOG 125) using an Erbium doped fiber source. We also present our approach to wavelength control.

Intermediate and Moderate grade Fiber Optic Gyroscope (FOG) have been developed for industrial applications such as Positioning system, Self-guided robots, and Bore-hole survey system. Those FOGs are based on the minimum reciprocal configuration with single mode fiber coil which reduces the production cost.

Draper Laboratory's experience with Interferometer Fiber Optic Gyro (IFOG) technology started via an Internal Research and Development effort in 1978. This work led to developing fiber optic gyros in which significant advances in IFOG component technologies, assembly, integration, and test were achieved. In excess of 30 patents have been issued to Draper as a result of this pioneering effort. More recently, Draper collaborated with JPL to transition their fiber optic breadboard gyro to a space qualifiable instrument for interplanetary long duration missions. During the initial phase, brassboard gyros were designed and fabricated that demonstrated performance that bettered NASA's CRAF-Cassini spacecraft objectives. In the second phase, the Engineering Model gyro was developed to meet mission qualification tests. Concurrent with this later phase, analysis, tests and qualification activities were performed to validate that gyro components would realize the required 16 year life. Two major inventions (patent pending) were conceived; one provides for continuous adaptive scale factor stability and the other integrates the optical source and photodetector into a single component [Source Integrated Detector (SID)], thereby eliminating a coupler and several splices thus reducing loss by 6 db. Using the above technologies and the implementation of common mode rejection of laser noise, Draper has defined a low noise high performance gyro in which rate power spectral density (PSD) is projected to be < 7 X 10^-7 (deg/hr)²/Hz. In those applications, where the PSD < 4 X 10^-5 (deg/hr)²/Hz is sought, a small size three component (SID, integrated optics circuit and fiber coil) gyro is easily implemented.

A fiber-optic gyroscope (FOG) is expected to be the next generation gyroscope for guidance and control, because of various advantages. We have been developing the FOG-Inertial Navigation and Guidance (ING) for M-V satellite launching rocket of the Institute of Space and Astronautical Science (ISAS) since 1990. The FOG-ING consists of an Inertial Measurement Unit (IMU) and an Central Processing Unit Assembly. At current status, the proto-flight model FOG-IMU is being actively developed. And the flight test of the FOG-ING was performed on February 20, 1993, aboard M-3SII-7 satellite launching rocket at the ISAS test facilities in Uchinoura, Japan. This paper presents the signal processing technologies of our FOG which are used for the above FOG-ING.

Fiber optic gyros of modest performance can be used as angular rate sensors for vehicle navigation on land. A practical design uses an open-loop configuration with an all-fiber optical system together with analog signal processing, which makes for low cost and simple construction. Initial production has started on a gyro whose principal components are all made from elliptical-core polarization holding fiber. The angle random walk is less than 10 deg/hr/rt-Hz with a maximum input rate of 100 deg/sec. The output is either an analog voltage which is proportional to rate or serial asynchronous data representing an incremental change in angle.

An integrated optical gyrochip has been developed for industrial and consumer fiber-optic gyroscope applications. The gyrochip is pigtailed with low-cost elliptical-core polarization- maintaining optical fiber. An alignment technique was developed that uses image processing technology to align the polarization axis of the fiber without launching light into its core. The fiber-to-fiber insertion loss deviation of the pigtailed waveguide was less than +/- 0.8 dB at a wavelength of 0.78 micrometers over 100 temperature-change cycles, ranging from -30 to +80 degree(s)C, with a fiber mode-field size as small as 3.5 X 2.6 micrometers .

Polarization problem and countermeasure in Resonator Fiber optic Gyros and Brillouin Fiber Optic Gyros are discussed. The Eigenstate of Polarization is introduced to express the behavior of the polarization in the fiber resonator. The polarization maintaining fiber resonator having 90 degree(s) rotation of the polarization axis at the splice and the single-polarization single-mode fiber resonator are discussed. Moreover, the way to realize a stable resonator using an ordinary single mode fiber is also presented.

Motivation is given for the development of dynamic and stochastic models of fiber optic gyros. Presented is a nonlinear system model of the fiber gyro's closed-loop optics and electronics that is simplified to a linear discrete dynamic model. Given are some of the issues arising in applying the discrete transfer function of the fiber gyro under deterministic forcing functions. The model is extended to include the gyro's output response to stochastic inputs. The resulting stochastic model includes the effects of the data acquisition system and quantization in the overall response. Discussed are techniques for evaluating the performance, both deterministic and random. Novel application of the Fourier filtering technique to simulate various types of random gyro noise, especially the mathematically pathological 1/f noise, is presented. A brief gallery of commonly applicable gyro noise is given.

Fiber optic gyroscopes (FOG) are solid-state rotation sensors that are appropriate for a wide variety of applications. In addition to becoming competitive with ring laser gyroscopes on new programs, FOGs are being manufactured to replace spinning wheel gyro technology in existing programs. The FOG brings with it the advantages of long life, high reliability, input axis stability, and low acceleration sensitivity. The AlliedSignal pointing grade fiber gyroscope was designed to replace a high-performance mechanical gyroscope currently made by AlliedSignal. Detailed passive thermal design, gyro assembly techniques, methods for rejecting light source intensity noise, and light source wavelength control are critical features that have been developed to produce a FOG with low noise, stable bias, and a stable and linear scale factor. Prototypes of this FOG have demonstrated angle random walk of 0.00021 deg/(root)hr and bias stability of 0.0006 deg/hr. Results of other performance tests and error models indicate that these gyros have a capability for random walk of 0.00012 deg/(root)hr and bias stability of 0.0004 deg/hr.

Smiths Industries (SI) is preparing a Fiber Optic Gyroscope (FOG) Inertial Measurement Unit (IMU) for incorporation into the Advanced Research Projects Agency Technology Reinvestment Project Fly-by-Light Advanced Systems Hardware (FLASH) laboratory demonstration. The IMU provides inertial data to the flight control system through the FLASH optical data bus and consists of three FOGs, three quasi-solid state accelerometers, sensor control electronics, a digital signal processor, and the optical data bus interface. Reliable, low cost solid state sensors are used to satisfy the performance requirements of the system. Specifically, the FOGs use state-of-the-art optical technology to measure aircraft rotations. FOGs have no moving parts and are therefore more reliable and durable than spinning wheel gyroscopes. Many FOG designs are based on a multitude of individual optical components and sensing coils fabricated from expensive polarization preserving fiber. Smiths Industries has developed a FOG design which uses low cost, commercially available single mode fiber in the rate sensing coils and makes maximum use of integrated optics to reduce cost and complexity. This sensor has demonstrated excellent tactical grade performance in a wide range of strenuous test environments. The SI FOG IMU is an important contributor to the performance, reliability, cost, and capability advantages of the FLASH system.

In order for the resonator fiber optic gyroscope to achieve navigation grade performance, it must employ an optical frequency shifting technique for high scale factor accuracy. Serrodyne phase modulation commonly used in interferometric fiber optic gyros, has been considered a leading choice of modulation techniques. Here we present theoretical analysis on the effects of imperfect serrodyne phase modulation along with experimental results. A solution for substantially reducing the rotation sensing errors associated with imperfect serrodyne is also presented.

This paper describes a study on the effects of scattering between polarization states in the sense loop of depolarized Interferometric Fiber Optic Gyros. The focus of this study is on the effects of component imperfections (polarizers, depolarizers, etc.). In this approach a single scattering center is assumed to exist at an arbitrary point in the sense loop. Insight is gained into the relative importance of the various components and their imperfections.

We briefly review the theory of fundamental thermal induced phase fluctuations in the fiber- loop of a Sagnac interferometer and compare it to novel experimental data. Loop lengths of 1.1 and 2.2 km are considered, showing phase noise levels between approximately 0.2 - 1.4 (mu) rad rms/(root)Hz in the frequency range 1 - 100 kHz. Excellent agreement between theory and experiment is demonstrated, showing that this noise source can have considerable impact on the threshold detection of a Sagnac interferometer based sensor for both detection of reciprocal and non-reciprocal measurands, using practical system parameters. We discuss the impact of this noise source when the Sagnac interferometer is configured for rotation sensing, and show the dependence of the random walk coefficient when the bias frequency and system parameters are varied.

A thorough investigation of the temperature induced performance errors of IFOG configured fiber gyros was performed. The investigation was focused on low-cost optical components which are capable of being assembled into a gyro package volume of less than two cubic inches including electronics. Testing performed at the optical component level includes diode sources, receivers, wound coils, and integrated optic assemblies. Testing also included the fabrication of IFOG circuits and performing gyro bias and noise measurements. The test results indicate that high performance rate sensing is possible given the use of low cost optical components.

The experimental demonstration of an all-fiber resonator optic gyroscope employing a spliceless PM-fiber resonator with 90 degree(s) polarization rotation in the lapped coupler is presented. A Frequency Modulation spectroscopy technique has been demonstrated for rotation sensing using two piezoelectric transducer phase modulators. The short term bias stability better than 16 degree/hr with integration time of 10 sec has been obtained. The main error sources of optical system are discussed and some reduction measures are suggested.

The paper describes three examples of low-cost, low-power signal processing techniques used in building prototypes of low/medium performance Fiber Optic Gyroscopes. The prototypes were developed at the Mercer Engineering Research Center, in an ongoing U.S. Air Force funded effort to develop a Fiber Optic Gyroscope replacement for existing mechanical rate gyroscopes used in a wide variety of applications. The novelty of applied methods consists of a very small number of elements used, and a very low power consumed by the signal processing electronics. The noise suppression was achieved due to small number of elements, synchronous homodyne detection scheme, and resonance amplifier/filter techniques. The Sagnac interferometric optics with 50/50 splitter/combiner, and 2 X 2 directional coupler, and optical phase shifter at 820 nm and 1500 nm wavelengths have been developed as a part of this ongoing effort and were used in the experiments.

3M has developed and commercialized a line of specialty single-mode fibers to meet the unique requirements of advanced fiber optic sensor applications. 3M implements a dual- technology approach which combines novel materials technology with optical waveguide design to produce high-performance fibers which have been qualified in many military and aerospace programs. The 3M product offering includes high numerical aperture single-mode fibers which tightly confine the guided mode to resist bending losses in miniature sensor packaging configurations. 3M offers a complete line of polarization-control fiber products to allow all-fiber construction of sensor optical circuits. Standard polarization-maintaining fibers that feature reduced size and high numerical aperture are designed specifically for use in high- density, miniature sensor coil applications. 3M single-polarization (polarizing) fiber is remarkably versatile, enabling system construction and packaging previously limited by conventional polarizer technology. All 3M polarization-control products employ unique coating and packaging materials to meet demanding optical and mechanical specifications from -55 degree(s)C to +85 degree(s)C. Fiber specifications and performance data, including radiation performance, will be presented along with strength and reliability data.

This paper surveys a variety of special fibers which have been developed for the sensor and component markets, based upon the polarization-maintaining and absorption-reducing design. Various types of polarization-maintaining fibers, rare-earth doped fibers, image-transmitting fibers, and other special fibers will be discussed.

The long-term mechanical reliability of polarization-maintaining and single-polarization single mode optical fibers drawn from ground preforms is of growing interest. This paper will report the results of the static fatigue tensile strength behavior under axial load at ambient conditions for PM and PZ types of single mode fiber produced from five ground preforms. The measured values of the fatigue resistance parameters N (22.6 +/- 1.3 to 27.9 +/- 1.5) are consistently higher than the N-parameter of 19.7 +/- 0.5 measured under identical conditions for standard commercially available single-mode fiber drawn from non-ground preforms. Large Weibull moduli of fiber from ground preforms suggest fiber of uniform strength distribution. Although fractographic analyses of failed fiber end faces do show extrinsic failure modes due to micro-cracks and zirconia particulates and intrinsic failures due to molybdenum inclusions, the analyses do not reveal failure modes peculiar to diamond grinding or high internal stresses.

Organic polymeric materials and devices have attracted considerable attention in recent years. Non-linear optical polymers have show promise of very high electro-optical coefficients and useful device characteristics with compatible device processing on semiconductor wafers leading to development of compact, high reliability OEICs. In this paper, the state-of-the-art technology and performance of polymeric integrated optical waveguide devices will be received and feasibility of using these devices as sensor elements (e.g., to measure temperature, pressure, displacement, vibration, chemical analysis, etc.) and also as components in optical sensor subsystems (e.g., optical gyro chip) explored.

Two different types of 3 X 3 couplers, symmetric and quadrature, can be used for passive homodyne Mach-Zehnder optical fiber interferometry. The former provides intensity outputs proportional to cos(phi) that are shifted 120 degree(s) apart, and the latter linear combination of sin(phi) and cos(phi) , where (phi) is the optical phase difference between the sensing and reference arms. Many demodulation algorithms, both analog and digital, have been developed. Demodulation with both 3 X 3 couplers is simulated to determine the performance of algorithms when noise exists in the coupler outputs because of uncontrolled environmental inputs. Results of simulations and experimental evaluations of several demodulation schemes found in the literature are evaluated for comparison purposes. The simulation developed for this study can be used to evaluate different 3 X 3 coupler digital demodulation methods using experimental data as well as contrived numerical inputs.

We have completed feasibility tests on a system to measure the internal temperature of hot steel workpieces. The system is based on laser generation of ultrasound and consists of a high power pulsed laser which shines on one surface of the workpiece. Each high power laser pulse ablates a small amount of material and the reaction forces create a longitudinal ultrasonic wave in the steel. A separate laser interferometer measures the arrival of the ultrasonic pulse at the opposite surface of the workpiece. Measurement of the time-of-flight of the ultrasonic pulse enables the velocity of sound to be computed. The velocity of sound is a known function of temperature in steel materials, and so the average temperature of the steel along the path of the ultrasonic wave can be determined. This system has several applications in the heavy metals industry, and feasibility tests were conducted on several different steel alloys. Laser generation and detection of ultrasound was demonstrated at temperatures above 1250 degree(s)C. Details of the measurement system will be described and results of the feasibility tests will be presented.

In this paper we present a new method of evaluating temperature distribution in electrical discharges: the method makes use of an Fabry-Perot optical fiber interferometer. The all- dielectric nature of optical fiber sensors, together with their immunity to electromagnetic interference, makes them ideally suited for the study of electrical discharges. As opposed to point-probe techniques, our method uses an integrating approach which takes advantage of the axial symmetry which is usually associated with practical discharge arrangements. Experimental results obtained in an Argon glow discharge are presented.

A prototype single-mode fiber-based Fizeau interferometric medical temperature sensor using coherence reading signal processing and mechanical amplification in the sensor design has been optimally designed and constructed. A measurement resolution of 0.006 degree(s)C and a 1% of span linearity over a temperature range of 27.3 approximately 62.5 degree(s)C have been achieved. This miniature sensor is expected to be a practical approach for most medical applications after further engineering.

The authors have previously reported the use of liquid crystals as transducing elements in novel configurations. The use of liquid crystals in these devices relies on the temperature dependence of their alignment and relaxation times when activated in an LCD, as opposed to their more conventional usage when it is their color change with temperature that is utilized. The liquid crystals in these latter instances have been thermotropic, and have not been activated in an electrical fashion. This paper reports the further development of a sensor which uses the temperature dependence of the activation voltage of the liquid crystals in an LCD. The device is self-referenced in that two time-multiplexed signals are produced when the LCD is alternately activated and inactivated. The output signal is a ratio of these two signals and the division is performed using a look-up table. The sensitivity of the system has been increased and additional features added to detect both damage to the probe head/optical fiber and excursion beyond the specific temperature range.

A new thermally-compensated bending gauge using surface-mounted fiber Bragg gratings is demonstrated. The gauge configuration involves two fiber Bragg gratings, surface-mounted on opposite surfaces of a bent mechanical structure. Experimental results using a cantilever beam are presented, showing a strain resolution of 9 microstrain.

This issue presents a new kind of crystal fiber high temperature sensor. The method of making the mini-blackbody by doping in the fiber end is found to be effective. The experimental performance of the fiber sensor was also reported.

A new kind of SCF (Single Crystal Fiber), Y-ZrO₂ (Y₂O₃ stabilized ZrO₂) SCF has been provided to substitute for Al₂O₃ SCF in high-temperature optic sensors, comparing for Al₂O₃ SCF, it has a higher melting point which can enable sensors to be operated at a higher temperature (> 2000 degree(s)C). In this paper, Y-ZrO₂ SCF is grown by means of Laser Heated Pedestal Growth method, its growth and optical characteristics have been studied, fibers with diameters of 300 - 500 micrometers and lengths of 100 - 250 mm have been obtained. Experimental results show that these Y-ZrO₂ SCFs can be possibly used in high-temperature optic sensors.

A novel method for measurement of rotational speed for reflective (machined or polished) shafts is presented. The method is based on Fourier transforming the scattered field from a single laser beam that illuminates the target. The detected intensity at two spatially separated positions in the Fourier plane will provide two signals, which, to a high degree, are identical except for a time delay. Tracking of the time delay for maximum covariance thus facilitates temporal probing of the instantaneous rotational speed and torsional vibrations. The method is insensitive to the shape and radius of the rotating shaft and to any additional translational motion. Further, the signal level is usually superior to the level in the existing method because direct reflection is detected. Mounting of retroreflective tape is, therefore, not required. A theoretical description is given with measurements based on using a delay-locked loop

Choosing the best optical fiber for a fiber-optic sensor application is a formidable task. There are many types of fiber sensors and a similar number of commercially available fiber types from which the sensor designer must choose. The task is made more difficult by the fact that no general guidelines have been established for selecting and designing fibers for fiber-optic sensors. In this paper, we propose a general approach as the first step toward developing practical guidelines for sensor designers. Our approach emphasizes the interaction between the sensor designer and the fiber supplier in the fiber selection/design process. We have developed the term, Application-Specific Optical Fiber, to highlight the importance of the linkage between application requirements and fiber design attributes. Several design tradeoffs are considered as examples of how to apply our approach.