Progress in fiber-optic gyroscope development at Honeywell is reported here. The results illustrate the versatility of the technology, showing its potential to meet both the low-cost, small-sized needs of tactical guidance, as well as the very high perfomance needs of inertial navigation and precision applications. In the case of inertial navigation, data is presented that illustrates the possibility of employing a low-cost depolarized design for this use.

We present solutions to reduce noise in depolarized gyros using low cost laser sources at 1.3 micrometers . Noise reduction is obtained by operating the source in the coherence collapsed regimen, by having the proper depolarizer design and by setting the proper phase modulation depth for optimum signal-to-noise ratio.

The prototype of an optical gyro encoder (OGE) has been successfully tested on the NTT telescope in September '93. The OGE consists of a ring laser gyro and a fiber optic gyro with their input axis parallel. The gyro outptu signals are compensated for earth rotation and misalignment and are subsequently integrated to get the angles. An adaptive digital control loop locks the fiber optic gyro to the laser gyro data. Thus the combined output has the precision of the laser gyro and the low noise of the fiber optic gyro. Specifically, the bias stability is better than 2 X 10^-3 deg/h, the scale factor accuracy better than 1 ppm, the random walk coefficient better than 5 X 10^-4 deg/(root)h and the resolution better than 3 X 10^-4 arcsec. The OGE has been mounted in the altitude and in the azimuthy axis of the telescope. The data were compared with the telescope disk encoder data. The test data show that the pointing accuracy is about 1 arcsec and the tracking accuracy 0.1 arcsec over a time of 30 seconds. This accuracy is sufficient for the very large telescope, for instance.

Requirements for a gyroscope intended for use in land navigation in a coupled dead- reckoning/GPS navigation system are governed more by economics than by performance. As a result, explicit performance requirements are poorly defined by the users. The development of a low-cost fiber optic gyro for this application is described. Using a short coil length, and simple packaging concepts, it represents an evolutionary approach to meeting evolving specifications. Based on elliptical-core polarization maintaining D fiber, fused fiber couplers and an on-fiber polarizer, the components are assembled by fusion splicing. The optical circuit loss is low, permitting use of a low power optical source. Signal processing is considerably simpler than for stand-alone inertial navigation systems, and the challenge is to minimize cost. The packaging concept is intended to facilitate assembly.

We describe amplitude-type polarization errors in depolarized fiber gyros and show a management scheme for their suppression. Prototypes operating both at 0.8 micrometers and 1.3 micrometers wavelengths exhibiting navigation grade drift and noise performance have been realized.

This paper treats the Brillouin backscattering in a single mode optical fiber and its implications on the Brillouin Ring Laser Gyroscope (BRLG). The BRLG consists of a fiber ring cavity in which stimulated Brillouin scattering is induced and provides two resonant counterpropagating backscattered waves. If this cavity is rotating around its axis, the backscattered waves get different resonant frequencies because of the Sagnac effect. The frequency difference is proportional to the rotation rate (Omega) by inducing a frequency offset between the counterpropagating waves. Some reported Brillouin spectra exhibit several peaks, which means that one pump wave provides at least two backscattered waves with distinguishable frequencies. In order to understand this multi-backscattering and to take advantage of it for the BRLG, we present results of a simulation of the Brillouin backscattering in a single mode optical fiber.

A complex optical transfer function of the Sagnac interferometer consisting of an integrated optical chip and a single-mode fiber coil is calculated. The fiber and the chip attenuation coefficients, refractive indices, and the lengths of the paths in the fiber and in the chip were included. To that purpose, the multiple Fresnel reflections as well as the gap width between the fiber and the chip were taken into account. By means of this transfer function, the influence of the spectral width of the light source on the level of the output signal and on the interferometer selectivity are determined. Finally, an antireflection configuration is proposed and analyzed and the influence of the polarizer and the phase modulator chip position on the interferometer selectivity are discussed.

This paper describes to the best of our knowledge the first implementation of a lithium niobate based 8 bit electroded integrated optic waveguide fiber optic gyro chip referred here as 'Digi- MIOC' (digital-electroded multifunction integrated optic chip, which has been used in a Sagnac effect exploiting microfiber optic rate sensor ((mu) -FORS) developed by LITEF. The paper highlights various features of a Digi-MIOC, such as design philosophy, fabrication aspects, and test procedures to evaluate static and dynamic characteristics of the electro-optic parameters. When used in closed loop operation, the Digi-MIOC forms the key optical component of a (mu) -FORS to aid the required optical-to-electrical signal processing to give linear output for input rates of rotation. Various test results and features of LITEF's (mu) - FORS, such as small size, large rotation rate measurement potential, low drive power, and high reliabliity are also highlighted.

The polarization-rotating resonator was developed to reduce temperature dependent polarization errors of a resonator fiber optic gyroscope for navigation-grade applications. Residual temperature dependent fluctuation of the symmetry of the resonance features limits the gyroscope performance. We present a fabrication technique, involving white-light interferometry, that yields a passive stabilized resonator. Experimental results show greatly improved resonator thermal stability.

A mutual phase shift of two counterrotating optical waves in a coil is placed. For the given temperature field, an exact formula describing the total Sagnac phase shift of both the waves is derived in the paper. On the basis of this formula, all the temperature effects are discussed generally and in two special cases: in the linear and periodic temperature fields. At the end of the paper, two possibilites of thermal stabilization of the fiber coil are proposed and discussed.

This paper will describe the implementation of a twin Mach-Zehnder reference interferometer in an integrated optics substrate. From measurements of the fringe visibilites an identification of the fringe order is effected, thus providing an absolute sensor for any parameter capable of modifying the difference in path length between two interfering optical paths. Such interferometers also are readily multiplexed into a quasi-distributed system.

It has been known for some time that the presence of NO plays an important part in the degradation of organic pollutants and in the formation of ozone and nitric acid in the troposphere. In recent years, there has been a significant increase in the concentration of atmospheric NO_x and a consequent decrease in air quality. The authors believe that there is now a need for a computer-controlled, near-real time monitoring system for atmospheric gas samples taken from a large urban area. This paper describes a laser-based REMPI procedure which utilizes a high power pulsed laser, atmospheric pressure ionization chamber and data acquisition system and, with detection limits as low as 1 ppb, it may well form the basis of such a system.

A simple fiber optic microphone was developed. The sensor operates on the well known principle of reflective sensors where the optical fibers are used as a source and modulated light collecting medium. The optical fiber reflective sensor was applied as a vibration detector of a membrane isntrument. The sensor characteristic was found linear for displacement amplitudes up to 0.6 mm for the large core fiber optic sensor. The measured signals were compared to signals from a commercial dynamic microphone. The test results indicate that the fiber optic microphone is capable of detecting lower frequencies that the high quality dynamic audio microphone.

In the paper-making process, wood chips are cooked to form a pulp, which is subsequently washed, bleached, and rolled into sheets. The mechanical strength, uniformity, and amount of bleach necessary to whiten the paper all depend on the lignin concentration in the wood pulp. In this presentation, we describe the developement of a laser-induced fluorescence method to measure lignin concentration in wood pulp, application of the method to characterize hundreds of different pulp samples obtained from different kinds of wood, and correlation of the results with industry-standard wet chemical Kappa number tests. We report the results of detailed characterization tests performed to determine the sensitivity and repeatability of the method and to quantify cross-sensitivity to other variables such as temperature, consistency, and pH.

This paper discloses a new fiber optic differential pressure sensor for liquid level measurement and control. The intended application is for US Navy use in automated shipboard machinery control and monitoring and damage control systems. The sensor has been developed in response to the need for an inexpensive, yet rugged and reliable liquid level sensor, compatible with advanced automated control systems, and suitable for use in hostile and difficult environments. The sensor is developed from an existing commerical design of a low- finesse, short-cavity Fabry-Perot pressure sensor. The sensor consists of a glass micro-chip etched with a shallow, optical cavity capped by a pressure sensitive silicon diaphragm. The Fabry-Perot cavity is vented to the chip base so that a differential pressure can be developed across the diaphragm. The micro-chip is fused to the optical fiber and housed in a protective capillary tube. The differential pressure developed across the diaphragm changes the depth of the Fabry-Perot cavity. This is sensed by measuring the shift in the reflected spectrum of the source LED using a dichroic ratio technique. Experimental models of the senosrs have been evaluated successfully on a US Navy test ship, the ex-USS SHADWELL. Since it is a true differential pressure sensor, it can be used in both pressurized and unpressurized fluid tanks. The sensor's performance and cost attributes should make this technology suitable for many industrial process and control applications.

A Tm-Ho co-doped optical fiber laser exhibits significant fluorescence between 1.6 and 2.1 micrometers . Such a fiber can from the basis of a gas detection system, since many gases of interest have overtone absorption bands in this wavelength region: in particular, carbon dioxide, methane, arsine, replacement gases for refrigerants, and nitrous oxide. Using this fiber we have demonstrated a simple shceme for the detection of overtone absorption bands of carbon dioxide in the 2 micrometers region. The detection sensitivity for carbon dioxide with this present method is of the order of 1%.

We discuss two of the latest demonstrations of the extrinsic Fabry-Perot interferometer (EFPI) sensor, namely a novel silica fiber-based hydrogen sensor and a high-temperature, sapphire fiber-based displacement sensor for surface strain measurements at temperatures up to 2000 degrees C. To modify the EFPI sensor for the detection of hydrogen, the sensor is sputter coated with a 2 micrometers layer of palladium. Based on the signal-to-noise ratio of the sensor, a minimum detectable hydrogen concentration of 35 ppm has been obtained. For displacement measurements at temperatures above the melting point of silica, we discuss results using a sapphire fiber EFPI sensing head demodulated using white light scanning Michelson interferometer.

Experimental and theoretical investigations demonstrate the possible performance of a distributed temperature sensor based on Brillouin optical time domain analysis. The Brillouin frequency, its thermal coefficient and the gain bandwidth were measured for several standard telecommunication fibers at 1.3 micrometers . Theoretical investigations show that especially for sensor fibers with lengths of several ten kilometers the powers of the pump and the stokes laser in a pump-probe configuration are very critical parmaters. The optimum power level and the resulting sensor performance are calculated for different fiber lengths. A possible sensor configuration is presented.

Under contract to the Morgantown (WV) Energy Technology Center for the Office of Technology Development (EM-50), US Department of Energy, we are developing a multipoint radiation monitoring system for long-term, continuous monitoring of radiation levels in the vadose zone of radioactive waste sites. The system is based on gamma detection with lightguide-coupled scintillator built into a probe buried in the ground. The lightguide transmits the visible light pulses produced by the scintillator to the surface where detection and signal multiplexing take place. The system is to be capable of monitoring large numbers of such passive probes which are to be permanently installed throughout the waste site. We have recently completed tests of a prototype single-probe system. In this paper, we report on the development and testing of the single-probe system.

We report design considerations and performance data of a fiber optic pressure sensor system that is suitable for continouus cobustion pressure measurements. The sensor is designed for 0 to 1000 psi pressure range and sensor housing temperatures ranging from -40 degrees C to 300 degrees C. A durable metal diaphragm design ensures fatigue-resistant long-term sensor operation and linear response. An intelligent autoreferencing technique provides drift- free output and compensates for high temperature and other environmental effects. Performance data is presented from tests performed in passenger cars and large-bore stationary engines. Typical sensor accuracy is +/- 1% at constant temperature and when connected to different interface units. Continuing endurance tests demonstrate excellent sensor durability for over 2000 hours continuous operation or 200 million pressure cycles that the sensors have been exposed to so far. The FiberPSI^TM pressure sensor system, commercially viable at this time, meets or exceeds the performance of research grade pressure sensors at a fraction of the cost.

For a highly accurate electro-optic sensor, the tolerance of the quarter-wave plate phase retardation should be at least (lambda) /250, and the azimuthal alignment error should be within +/- 0.5 degrees. Also the phase retardation depends on the angle of incidence, which makes the alignment more difficult. The method we present uses the extinction ratio as a measure of the quality of alignment. It enables in-situ alignment of the quarter-wave plate to the phase retardation accuracy of +/- 0.5 degrees using only the components of the electro- optic sensor. The method can easily be generalized for any application and for an automated and direct measurement of the phase retardation of a wave plate with high accuracy.

Two detection schemes utilizing a two-mode fiber waveguide as an intrinsic sensor are presented in the case when a low-coherence source is used and no observable interference pattern exists at the exit face of the fiber waveguide. In the first detection scheme the sensor configuration is used which consists of a two-mode fiber waveguide and a high-resolution spectrometer placed at its output. In the second detection scheme the output optical field of the two-mode fiber waveguide is analyzed in the Michelson interferometer configuration by a low- resolution spectrometer. It has theoretically been shown that in both detection schemes the spectral modulation is present which is closely connected with both the measured and intermodal dispersion. However, the sensor operation of the second detection scheme is constrained by the optical path difference (OPD) in the Michelson interfermeter which is not only greater than the source coherence length, but is also adjusted to match the group OPD between guided modes.

For the desired improvement of electromagnetic compatibility using optical current transformers a separation of optical sensor head and electronic components by an optical link is required. Intensity modulated optical output signals of a polarimetric fiber optic current transformer can easily be transmitted by standard multimode fibers. A realization of the supply of a sensor fiber with linearly polarized light employing low cost standard monomode fiber is presented here. It is based on the transportation of depolarized optical waves and recovery of lineraly polarized light by a linear polarizer. First three methods of depolarizing optical waves emerging a semiconductor laser source using birefringent materials are theoretically described. They make use of a crystal wedge depolarizer, a crystal Lyot-depolarizer and a fiber Lyot- depolarizer. All methods are reflected on simplicity in handling and possiblity of low cost realization. A Lyot depolarizer employing a high birefringent fiber is chosen and tested. A single ended device of a polarimetric fiber optic current transformer with twisted sensor fiber is provided with such an optical link which transfer characteristics are not influenced by the birefringence properties of standard single mode fibers.

A differentiating interferometer is proposed for measuring time varying signals. The system comprising a modified fiber ring resonator was implemented to measure electrical current. The modified ring resonator consists of a length of fiber between one of the input and output ports of a directional coupler. This length of fiber forms a delay line resulting in a constant delay time. The other coupler output port is connected to the sensing element and a reflector. By means of the delay time, the interferometer detects the derivative of the unknown perturbation signal at the common input/output port of the interferometer. Since the total path length imbalance is zero, a short coherence length source such as a light emitting diode can be used. The inherent properties of the interferometer also ensures insensitivity to slowly varying fluctuations such as temperature drift. With the introduction of frequency domain multiplexing, the sensor can easily be expanded into a multiplexed sensor system to measure multiple signals. Current measurement is achieved by means of a current transformer terminated with a resisitive load. The resulting potential difference across the load drives a piezoelectric ring which in turn phase modulates the optical signal. Results of a frequency multiplexed two element 50Hz current sonsor will be discussed.

We present optical sensors for the measurement of electric and magnetic fields in an anatomically and dielectrically correct biological phantom of the human head generated by a personal communication device. The sensor is based on all-dielectric optical probes, coupled by fiber optics to the remote light sources and signal processing electronics. The electric field probe utilizes Pockel's effect in cadmium telluride, while the magnetic field probe is based on Faraday effect in cadmium manganese telluride. The anticipated measurement sensitivity is 2 V/m (E field) and 0.25 (mu) T (H field), with spatial resolution of 1 cm. Frequency range is 1.8 GHz, and dynamic range is > 60 dB. Both sensors utilize polarimetric optical scheme.

A high-accuracy optical current sensor (OCS) utilizing the Faraday effect is proposed. By making use of the characteristics of wide bandwidth of OCS and according to superposition theory, a reference sinusoidal wave ac current with stable amplitude and different frequency from measuring ac current is added to the same one SF-6 glass bulk ring which is used as sensing element. Then comparative measurement is carried out and the ratio of two output signals of the Faraday rotation is shown independent of ligh intensity, Verdet constant, and temperature. Experiments performed at room temperature to 60 degrees C show that good linearity and accuracy can be obtained by using this method. The application of this method in actual environment is discussed.

A fiber-optic sensor has been developed to measure the lightening current. The lightening current which induces birefringence in a glass loop is to modulate a linearly polarized optical beam ((lambda) equals 0.85 micrometers ). The modulated optical information is transmitted to a PIN through an optical cable and converted to the electrical signal. A high-speed data acquisition system is used to sample the pulse signal. The waveform, rise time, peak value, and frequency components of the pulse signal can be shown on the screen of the computer.

The simple observation that the temperature coefficient of most structural materials in which strain may need to be measured differs from that of optical fiber measuring systems indicates immediately that both temperature and strain fields should be mapped with comparable accuracy in order to arrive at a reliable indication of mechanical strain. This paper initially defines the criteria for adequate compatibility between temperature and strain field measuement and then compares the techniques which have emerged in the past five years to address this problem. All techniques require the measurement of two optical parameters which are typically differential delays e.g. in interferometers and grating sensors or combined dellay and dispersion characteristics. The basic features of these measurement techniques will be addressed and comparisons made between the applicability of the various techniques. As an example, our own work measured temperature and strain to within +/- 2 C and 10 (mu) (epsilon) . Other work, e.g. with Bragg gratings achieves +/- a few tens of (mu) (epsilon) and a few degrees centrigrade.

We report noncontact measurement of temperature profiles in fluids by means of a novel laser beam deflection probe. We use optoacoustic generation by a pulsed Nd:YAG laser to emit a short acoustic transient wave within the fluid region under study. Propagation region several times before it reaches the deflection-detecting photodetector. A single oscilloscope trace of the photodetector output gives us then the timing of the acoustic wavefront at several distances from the source. By measuring the acoustic wavefront transit times and the distance between the probe beam segments we can determine local sound velocity and there from the local temperature.

Rare-earth materials doped into low-loss silica fibers are of interest for temperature sensing applications since the absorption properties of such are temperature dependant. Such absorption properties have been studied in ytterbium doped silica fiber using relative absorption and cut-back techniques at temperatures between 77 and 1163 K in the wavelength range 800 to 1150 nm. The wavelength dependant thermal sensitivity varies from -0.012 to 0.033 dB/K for a standardized one meter long 1000 ppm-doped fiber. These significant changes in absorption with temperature have been attributed to homogeneous line broadening. The fibers investigated show excellent potential for use as the sensing element in intrinsic fiber-optic high-temperture sensors.

The application of the processing technique based on straightforward detection of output spectrum of sensing interferometer for simultaneous measurement of temperature and strain is demonstrated. The processing algorithm includes the construction of an analytical signal from a nearly periodic part of the output signal in the spectral domain, and further analysis of its phase. The parameters of spectrometer, visibility, and signal-to-noise ratio of interference pattern also as the spectral bandwidth of the light source were optimized to provide the desired accuracy of temperature and strain definition and low level of cross-sensitivity.

Polymer dispersed liquid crystal inserted between two multimode optical fiber end faces forms the basis of an electric field probe. This probe has an active volume of about 0.001 mm³ and approximates a point measurement. The linear relation between detector output and electric field in the 600-800 V/cm range is adequate for most electric power distribution systems. As the contrast ratio of this transducer is large, it can be used as an on-off detector for high voltage equipment.

An all-fiber Fabry-Perot interferometer using coherence demultiplexing and rugate mirror reflectors grown with electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) on the fiber ends is proposed. The interferometer consists of a laser diode source, two optical fiber cavities, three rugate mirrors, a phase modulator and phase detection system. Coherence demultiplexing allowed the use of fiber cavities of several meters in length with a partially coherent illuminating light source. Truly inhomogeneous refractive index mirrors were designed taking into account dispersion and losses of SiO_xN_y at the required wavelength of 1.3 micrometers . The reflectance/transmittance ratio during growth were adjustable from 0.05/0.95 to 0.95/0.05 and mirrors used in the experimental interferometer had no inal reflectances of 40%, 68%, and 40% respectively. Design and fabrication procedures permit implementation of window functions and matching layers for flexible control over transmittance and reflectance charateristics. The long-cavity Fabry-Perot sensor was demonstrated for use as a strain gauge. Good agreement was shown with results obtained by a conventional strain gauge.