Real-time hoop strain measurement at multiple points along a flowline provides a way to monitor changes in the internal pressure gradient within the flowline. This information could be used to provide an early warning that a flow restriction is forming, locate the area of the blockage, and allow early intervention to control or eliminate deposition of material on the pipe wall. In the event of compete flow blockage, the method could be used to precisely locate the blockage. In this project, we evaluated fiber Bragg grating (FBG) sensors for measurement of hoop strain present in the wall of pressure pipe. The test were performed on a section of pipe to which multiple sensor were attached. The purpose of the testing was to characterize the hoop strain and axial strain. The advantage of FBG sensors for this application is that multiple sensors can be embedded in a single optical fiber which can then be attached to a pipeline. Each FBG sensor is wavelength encoded so that each sensors strain output signal corresponds to a known location along the length of the pipeline. Thus, it is possible to identify the location of a blockage in a pipeline by monitoring many locations along the pipe for small changes in hoop strain indicative of increased pressure drop. The presentation will include a description of the tests and analysis of the performance characterization work. The result of the tests were positive. Analysis of the data for this application shows that it is possible to achieve submicrostrain resolution and better than 2 microstrain repeatability with FBG sensors.

An optical fiber sensor with two fiber Bragg gratings in serial connection which is multiplexed in an optical wavelength domain is constructed to sense an acoustic field in water. Both the gratings are inserted between optical isolators in order to stabilize the sensor by suppressing Fabry-Perot interference in fiber that is caused by small reflections from fiber end facet, connectors and an optical coupler. The two gratings in the sensor are confirmed to work independently and have little influence on each other. Comparison of the experimental data to the theoretical prediction shows that the developed sensor can detect the relative phase between two points in the acoustic field and thereby determine the direction of the acoustic source. Since a fiber Bragg grating can make an optical sensor of high sensitivity and wide dynamic range and can be easily multiplexed with an arrayed structure in either one or two dimensions, it will then offer a convenient tool to measure distribution of amplitude and phase of an acoustic field in water.

We demonstrate that short in-fiber Bragg gratings coupled with an appropriate desensitization of the fiber, may be successfully used to measure MHz ultrasonic fields.

New digital demodulation algorithm for recently announced twin-grating fiber-optic sensor is presented. The sensor is built with two short, identical, low reflectance, closely spaced Bragg gratings imprinted in a telecommunications fiber. Because of such a design the reflection spectrum of this sensor is a sinusoidal wave within an envelope of the reflection spectrum of a single Bragg grating. Similar to traditional sensor based on Bragg gratings, the change of the temperature or strain leads to a shift of the reflection spectrum along the wavelength axis. However the reflection spectrum of the twin-grating sensor has more complicated structure and instead of measuring the position of gravity center of the spectrum we use more sophisticated algorithm to evaluate the measurands. Two computational methods are used to estimate the shift of the spectrum: evaluation of the phase of the sinusoidal wave and calculation of the position of the envelope. This combination of two different methods provides high accuracy of temperature or strain measurements. The ability of this sensor to provide simultaneous measurement of both temperature and axial strain is also demonstrated using computer simulation of twin-grating sensor in a Hi-Bi fiber.

A closed loop technique for measuring Bragg wavelength shifts based on active wavelength tuning of a WDM coupler is presented. By stretching the coupling region of a fused biconical WDM, the 3 dB point is set by the feedback loop to always match the reflected Bragg wavelength. With this scheme, sensitivities usually associated with highly selective WDM can be obtained without compromising the measurement range.

This paper describes SHAPE TAPE, a thin array of fiber optic curvature sensor laminated on a ribbon substrate, arranged to sense bend and twist. The resulting signals are used to build a 3D computer model containing six degrees of freedom position and orientation information for any location along the ribbon. The tape can be used to derive dynamic or static shape information from objects to which it is attached or scanned over. This is particularly useful where attachment is only partial, since shape tape 'knows where it is' relative to a starting location. Measurements can be performed where cameras cannot see, without the use of magnetic fields. Applications include simulation, film animation, computer aided design, robotics, biomechanics, and crash testing.

Brillouin Fiber Optic Gyro (B-FOG) can detect angular velocity from the beat frequency between the two lasing Stokes lights that circulate in opposite directions in the fiber ring resonator. This means the B-FOG has inherently the beat output format suitable for navigation applications. However, B-FOG has a serious problem called 'lock-in phenomenon'. In lower rotation rate, frequency pulling effect occurs between the two Stokes lights due to backscattering in the resonant, and the beat signal is getting distorted and finally locked to zero. In this report, at first, we realize B-FOG and observe its output characteristics, including optical Kerr-effect induced bias and the lock-in phenomenon. Then, the details of the lock-in phenomenon are evaluated theoretically. Additionally, we propose a novel method to avoid the lock-in phenomenon by modulating the gyro output through the optical Kerr-effect in the fiber resonator. Finally, we verify this method experimentally.

In this paper, we report a novel configuration of micro optic gyro (MOG), which is monolithically integrated on silica Planar Lightwave Circuit (PLC) with countermeasures for noise factors. Optical ring-resonator gyros suffer mainly form polarization fluctuation induced noise and backscattering induced noise. We adopt a stress applying amorphus silicon film as the countermeasure for the former, and binary phase shift keying (b-PSK) as the one for the latter. However, to apply b-PSK, thermo-optic (TO) phase modulation is the only one scheme available in silica waveguide, whose bandwidth is limited to approximately 1 KHz. To utilize the narrow bandwidth of the TO modulator effectively, we propose an electrical signal processing scheme and frequency compensating modulation waveform. We demonstrate the suppression of the backscattering induced noise as 7.6dB. Additionally the gyro output is observed with applying an equivalent rotation.

We have developed a technology to bend both singlemode and multimode optical fibers in radii as small as 0.45 mm without significant optical loss or breakage. This technology is of tremendous benefit for compact optical sensors in which it may be desired to reverse the direction of travel of the fiber within a very small sensing head. The bends utilize 'air cladding' to guide the light around the tight radius of the bend without loss. The bends can be packaged in small capsules 1.5 mm in diameter and less than 1 cm long. This miniature-bend technology avoids the 50 mm bend diameter required to reverse the direction of travel for conventional fibers. Miniature 180 degrees bends have been demonstrated with very low optical losses across the entire 1250 to 1650 nm spectral band. The same performance can be obtained in the 820 nm wavelength region. This revolutionary 'kernel' can be included within the sensing head, providing a very small cylindrical sensor whose pigtails exist from the same direction. This paper describes the optical and physical performance of the miniature fiber bend. Particular attention is paid to the measured IR attenuation spectra, polarization dependent loss, and reflectance. A long lifetime is estimated as a consequence of the annealing of the bend region during the fabrication procedure.

We have utilized a traveling acoustic pulse in a two-mode optical fiber to create a moving beam splitter to couple light from LP₀₁ to LP₁₁ mode. As these optical modes have different group velocities, a variable intermodal delay is generated as a function acoustic pulse position in the fiber. The device can be used in low-coherence interferometry to scan time delay for making fast extended range absolute measurement using simple analog electronic circuits. With this scanning technique we demonstrate measurement of absolute strain over 1600 (mu) (epsilon) in the temperature range 20-60 degrees C with resolutions of the order of 40 (mu) (epsilon) and 0.7 degrees C, respectively, employing highly birefringent fibers as sensing elements.

We have developed a fiberized OCT system which can deliver transversal and longitudinal images. The features and performance of the system are presented in terms of mode of operation, modulation method and image processing method.

Ford Motor Company had a requirement to measure fan belt vibration on their 4.6 liter Cobra-Mustang engine. While this sensor was to be used in the laboratory, it would also be used for field testing of this engine. The general operation temperature was -40 to 120 degrees C, but there was an engine 'soak-back' requirement of up to 200 degrees C. The vibration requirement was 3g continuous at 10 Hz with 20g shock. Humidity was 0-95 percent. Without active cooling, the temperature environment eliminated engine mounted electronics and with it some more common approaches such as laser triangulation based sensing. A laser radar concept was developed which features remotely located electronics, fiber optic delivery and return of the signal and an engine mounted optic head. The three lens design of the receive optics is a compromise choice designed to maximize power at the receiver over the full travel of the belt. The electronic scheme consists of a time-to-amplitude converter based on a precise time interval derived from the phase difference of logic level pulse trains which in turn are formed by the 'exclusive O Ring' of the transmit and receive pulses. In practice, a 10 MHz pulse train is transmitted to the vibrating belt which coupled with some fast electronics results in about 1 0.1 mm resolution, sufficient for this application.

In a conventional FTIR, the spectral content of the light is analyzed by a Michelson interferometer or other interferometer with a moving arm. The transmitted light intensity is measured by a wavelength-insensitive detector. The interferogram derived from a Michelson interferometer lies in the temporal domain. An alternative method for obtaining the interferogram involving no moving parts is demonstrated. For this, the interferogram lies in the spatial domain. This concept has many applications to sensor systems, for instance, forming a low-cost demodulator for Bragg-grating systems or field-portable spectrometers.

A new intensity modulated optical fiber vibration sensor has been employed to monitor the vibration signal in the smart composite structures in this paper. The advantages of this sensor ar the lower cost and the easy-to-use system. The sensor were fabricated using conventional 50/125 step-index multimode optical fibers and the custom-drawn epoxy resin capillary tube. The construction of this sensor is like the extrinsic Fabry-Perot interferometric. A face coupling theory of the intensity modulated fiber optic vibration sensor is developed. This optical fiber sensor has been embedded in the end of the smart composite cantilevered beam. The static and dynamic characteristics of this optical fiber vibration sensor have been tested. At the same time, the compared test of this sensor with commercial piezoelectric transducer are also finished. The experimental results show that the new type of intensity modulated optical fiber vibration sensor has higher sensitivity and better dynamic and static properties. The spectrum response of this sensor are also agreeable to that of the commercial transducer.

Fiber-optic displacement and vibration sensor are described in a single set up with higher dynamic range. Hard polymer clad silica fiber is used for both transmission and reception of light. The sensor system consists of coherent optical source, transmitting fiber, bi-convex lens, receiving fiber array, detectors and electronic circuitry. Light of (lambda) equals 980 nm is launched to transmitting fiber and light reflected from the target is received by fiber array and detected by p-i-n diode. Detected power of two adjacent fibers is subtracted by difference amplifier and followed by a level shifter. A mathematical model relating focal length of lens, radius of fiber, spacing between transmitting and receiving fiber, distance of the fiber from optical axis has been developed. The range of linear displacement, and angular displacement using four receiving fiber array is 0 to 1365 micrometers and 0 degrees to 0.5, respectively. The same concept of measurement is also applied to develop a vibration sensor. The range of measurement of peak to peak amplitude of vibration using three fiber array is obtained as 910 micrometers .

This paper presents a fiber-optic temperature measuring system which can be used for measuring the temperature in many occasions. The system is of reflective type and composed of thermostatic bimetal-plate, lever-piston framework, optical grating and optical fiber probes. When the temperature changes, the thermostatic bimetal-plate deforms. Through lever-piston framework, the optical grating produces displacement in the upright direction. Thus the change of the temperature is transformed into the upright displacement of the optical grating. Optical fiber probes are used for detecting the number of streak lines of the optical grating's displacement depending on the change of temperature. The detected signal can be transmitted to the control center through optical fiber cable up to distance of 1km. The measurable range of this system reaches 100 degrees C with accuracy of +/- 0.2 degrees C.

Optical fiber sensors, because of the small size, low weight, extremely high information carrying capability, immunity to electromagnetic interference, and large operational temperature range, provide numerous advantages over conventional electrically based sensors. This paper presents preliminary results from optical fiber sensor design for monitoring acceleration on aircraft. Flight testing of the final accelerometer design will be conducted on the F-18 Systems Research Aircraft at NASA Dryden Flight Research Center in Edwards, CA.

Fly-by-light has been a research and development area for the last 10 years, and much progress has been made in many areas and applications. Developments in fly-by-light component technologies such as vertical cavity surface emitting lasers (VCSELs) will be discussed to include the application of these types of laser to high-speed fiber- optic transmitters. Data will include digital transmission performance characteristics, the effects of temperature changes on the laser output and transmitter performance, and gigabit per second operation. A comparison will be made between typical edge emitter operation and VCSEL operation over similar temperature ranges. Both packaging and connectorization of individual transmitters and transmitter arrays will be discussed. Other VCSEL applications will be discussed including the application to Fiber Channel data links and networks. Fiber Channel data links can provide much larger data rates than current fly-by-light systems. The usefulness of redundant ring architectures and DWDM schemes will be discussed for both enhanced network reliability and speed.

We will report on the design and testing of a precision, remote, via fiber optics position transducer suitable for incorporation in a closed loop fly-by-light positioning system. The design is based on Visidyne developed technology for an ultra high resolution optical radar based on Continuous Wave modulated light at a frequency of 1 GHz. It produces digital position data with 12 bit precision e.g., for a travel distance, stroke of 6 inches or greater at a bandwidth, update rate of 1 KHz. The passive nature of the transducer at the actuator location and the high operating frequency makes it highly tolerant to even extreme levels of Electro Magnetic Interference and when constructed from high temperature material is can operate at temperatures well in excess of 300 degrees C. We will discuss transducer performance, precision and position stability with particular emphasis on the effects of length changes within the multi-mode optical fibers used to deliver and collect the light to and from the transducer. We will also discuss cost aspects of the design and their effect on overcoming market entry barriers.

Efficient, linear, broadband optical modulators are an essential component in wide bandwidth optical links for high fidelity distribution and processing of wideband signals. We discuss the packaging issues and remedies for the packaging of electroabsorption modulators for greater than 20 GHz link applications. The EAM is a waveguide semiconductor quantum well device which we have demonstrated to have a excellent linearity and electrical to optical conversion efficiency. Several important issues require resolution in order to produce a high bandwidth, packaged product. These include temperature control, EAM back-side metallization, attachment of EAM to submount, Product hermeticity, alignment and attachment of input and output fibers to the device at sub- micron tolerances, retaining this alignment over operational temperatures and anticipated vibration environments, and elimination of outgassing materials that may serve as failure initiators to optical facets. This paper addresses these issues.

The development of an aircraft-qualified 18-fiber optical ribbon cable was accomplished under the fly-by-light advanced system hardware program, sponsored by the Defense Advanced Research Projects Agency. This cable was developed because there was no suitable ribbon cable available which could survive the requirements of commercial transport and military tactical aircraft. In addition to developing this cable, aircraft-qualified of commercial transport and military tactical aircraft. In addition to developing this cable, aircraft-qualified connectors and conversion units to convert from the ribbon configuration to single-fiber configuration, referred to as 'fan-out boxes,' were also designed and constructed. All of this developed hardware flew aboard Boeing Company Aircraft Group-Long Beach Division's MD-90 test vehicle as part of the Fly-By-Light Optical Aileron Trim program.

In January of 1998 Boeing conducted successful flight testing of a prototype fly-by-light/power-by-wire concept demonstration system performing a flight control function. This paper discusses the demonstration system and the concepts it was designed to illustrate. Additionally, the aircraft installation and flight test effort will be overviewed.

Technology development in photonics is rapidly progressing. The concept of a Unified Network will provide re- configurable network access to platform sensors, Vehicle Management Systems, Stores and avionics. The re-configurable taps into the network will accommodate present interface standards and provide scaleability for the insertion of future interfaces. Significant to this development is the design and test of the Optical Backplane Interconnect System funded by Naval Air Systems Command and developed by Lockheed Martin Tactical Defense Systems - Eagan. OBIS results in the merging of the electrical backplane and the optical backplane, with interconnect fabric and card edge connectors finally providing adequate electrical and optical card access. Presently OBIS will support 1.2 Gb/s per fiber over multiples of 12 fibers per ribbon cable.

Sanders, a Lockheed Martin Company, is leading the development and integration of the Vehicle Health Management (VHM) system for Lockheed Martin's VentureStar Reusable Launch Vehicle. The primary objective of this effort is to provide an automated health status and decision-making system for the vehicle. A detailed simulation of the VHM system on RLV is currently being developed using the Foresight Design and Modeling Tool. The simulation will consists of models of key components of the RLV VHM system. An effective detailed system simulation will allow for system and design engineering, as well as program management teams, to accurately and efficiently system designs, analyze the behavior of current systems, and predict the feasibility of making smooth and cost-efficient transitions form older technologies to newer ones. This methodology will reduce program costs, decrease total program life-cycle time, and ultimately increase mission success.

As widely known, fiberoptics (FO) are being used in a large variety of sensor an systems particularly for their small dimensions and low cost, large bandwidth and favorable dielectric properties. These properties have allowed us to develop sensor and systems for general applications and, particularly, for biomedical engineering. The intravasculator pressure sensor was designed for small dimensions and high bandwidth. The system is based on light- intensity modulation technique and use a 2 mm-diameter elastomer membrane as the sensor element and a pigtailed laser as a light source. The optical power out put curve was linear for pressures within the range of 0 to 300 mmHg. The real time optical biosensor uses the evanescent field technique for monitoring Escherichia coli growth in culture media. The optical biosensor monitors interactions between the analytic and the evanescent field of an optical fiber passing through it. The FO based high voltage and current sensor is a measuring system designed for monitoring voltage and current in high voltage transmission lines. The linearity of the system is better than 2 percent in both ranges of 0 to 25 kV and 0 to 1000 A. The optical flowmeter uses a cross-correlation technique that analyzes two light beams crossing the flow separated by a fixed distance. The x-ray image sensor uses a scintillating FO array, one FO for each image pixel to form an image of the x-ray field. The systems described in this paper use general-purpose components including optical fibers and optoelectronic devices, which are readily available, and of low cost.

The concept of robust sensor of current and magnetic field was under consideration based on the use of polarization interferometer scheme. The scheme utilized broadband lightsource and single mode fiber with significant intrinsic birefringence comparable with the period of birefringence axes revolution, their ratio N being the main parameter both for sensor robustness and sensitivity determination. The external forces-originated perturbations were taken into account in the 'method of averaging' approximation and an optimal condition for number N was determined to suppress perturbations' influence. Even for perturbed case the polarization retardation in such a fiber was found not accumulating but varying periodically. Conditions for these varying terms to vanish due to source bandwidth averaging were evaluating.

This paper introduces optical fiber pressure senor nowadays in the world and describes their sensing principle, structure, test and application.

The work introduces an optical fiber voltage transformer based on the Pockels effect. The transformer is different from a conventional electric-magnetic voltage transformer. A crystal BGO is used as sensor that is sealed in SF₆ gas container; the measured signal is transferred by optical fiber in the Electro-Optical Voltage Transformer (EOVT). The principles and composition of EOVT is described here. The system consists of three parts: capacitive divider, optical sensor and electronics module. According to the analysis of factors that influence on the accuracy of measurement, the main ones, temperature and pressure of SF₆, are corrected by means of signal digital process. The performances of 110kV EOVT were tested. The results show that the accuracy of EOVT could achieve 0.5 percent. Compared to a conventional electric-magnetic voltage transformer, the advantages of 110kV EOVT are higher accuracy, low cost, small volume, excellent dynamic characteristics and immunity from electromagnetic interference. In particular the low voltage is effectively isolated from the high voltage by means of the optical fiber.

The application of the technique of synthesis of optical coherence function for detection in scattering medium is investigated. By modulating the optical frequency, the technique synthesize the coherence function into a delta- function-like peak at an arbitrary location, and thus can detect interferometrically the information at that location. The location is adjustable by the modulation parameter or additional phase modulation. A multi-section super-structure grating distributed Bragg reflector laser diode of THz-order tunable range is employed to enhance the spatial resolution for suppression the multiple scattering form locations other than that detected. In a primary experimental demonstration, a reflectometry of 550 micrometers spatial resolution has been built up and was used to detect scattering medium.

We describe work on a system able to measure the temperature at a number of points along a single optical fiber probe, designed for in-vivo temperature profile monitoring. The sensing elements are in-fiber Bragg grating sensor and three forms of signal processing have been investigated. System 1 uses interferometric wavelength shift detection with a monochromator providing the WDM. System 2 used a scanning in-line Fabry-Perot filter and system 3 uses a monochromator with a CCD based readout scheme. The performances of the three approaches are compared.

As part of a project to optimize hybrid laminates for resistance to fatigue failure, arrays of fiber Bragg gratings are being used to monitor small-scale strain perturbations in composite materials. A remote multiplexed sensing system with 40 remote sensing sties using fiber optic technology, has been developed to monitor the strain field developed across the composite lamina of a hybrid laminate in the vicinity of a fatigue crack. Developed primarily for fatigue-critical aerospace applications, i.e. fuselage and lower wing skins, the hybrid laminates are orthotropic materials having lower density and higher strength than a simple alloy monolith without reinforcement. Fatigue crack growth in hybrid laminates is a complex process that involves a combination of delamination and fiber bridging. The fiber optic system has been applied to the problem of characterizing delamination zone development about a fatigue crack, initiated at a through-thickness fastener hole.

The development of a new fiber Bragg grating multiplexing technique is reported. The technique is based on a twin Bragg grating sensor configuration and exploits a combination of wavelength- and frequency-domain multiplexing. We demonstrate that very weak Bragg gratings with reflexivity of approximately 0.5 percent or less can be efficiently used by this technique. Experimental results presented in the paper and theoretical estimates indicate that the interrogation of more than 100-element serial array sensor system is feasible.

We report on the integration of optical fiber containing Bragg gratings in the structure of both optical and power cables. It is hon that fiber Bragg gratings provide an efficient method to monitor quasi-distributed mechanical strength along optical cables. This technology is also applied to the monitoring of temperature in power cables for transmission/distribution infrastructures. We show that there are no losses introduced during the cabling process, and the temperature sensitivity of the fiber Bragg grating was found to be only slightly affected by the extrusion process. Results are presented for cable operation in real environment.

Distributed optical fiber temperature sensing (DTS) provides an elegant way of monitoring the temperature at many points without necessitating the accurate positioning of individual discrete sensors. This paper demonstrates recent advances in distributed temperature sensing based on spontaneous Brillouin scattering. A high spatial and temperature resolution is achieved by exploiting a novel low cost detection system. The experimental configuration consists of two key components; a Q-switched laser source to generate the backscattered signal and the low cost detection system which comprises an in-fiber double pass Mach-Zehnder interferometer and a sensitive InGaAs APD connected to a computer based averaging system. It is the relative low cost of these components which has made the Brillouin based temperature sensor so attractive for commercial exploitation. A spatial resolution of 3.0 meters with a Brillouin temperature resolution of 0.9 degrees C at a range of 16km has been achieved.

Two high resolution optical-fiber system for the distributed measurement of strain or temperature have been investigated. The first is a fully distributed system, based on a high spatial resolution POTDR which benefits from photon-counting detection, with a spatial resolution of 50mm. The second is a novel quasi-distributed system which uses coherent coupling of backscattered light in a high birefringence fiber, and also uses photon counting detection.

This paper present a new concept in the design of distributed fiber-optic sensor systems for in situ monitoring of leaks in lined landfills. The concept utilizes disposable sensor that cut the fiber selectivity and thereby disclose the location of the leak. The demonstrated advantage of the sensor is simplicity and the ability to operate reliably in harsh environments. The anticipated advantages are low cost, high long-term reliability and simple installation. The novel features of the leak detection systems are that in addition to its potential for detecting leaks in situ, it can pinpoint leak location and the rate of spread. the leak detection system has two major benefits, it can lower the cost of ground water and soil sampling and it can play an important role in risk assessments of landfills and hazardous waste sites.

A modified reciprocal reflection interferometer (MRRI) with passive demodulation scheme (PDS) has been proposed for the implementations of time-division multiplexing optical fiber current senor (OFCS) system. The PDS to simplify the demodulating systems of OFCS has been developed. Descriptions of theory as well as experimental verification are presented. A good linear demodulation result is obtained. The Verdet constant measured experimentally is 4.2 (mu) rad/A*turns, in good agreement with the literatural data. By using the proposed modified reciprocal reflection interferometer, an OFCS is able to become insensitive to environment perturbations. The OFCS's noises that arise from its lead fiber disturbed by vibrating perturbations can be retrained over 20dB compared with the noises of an OFCS using a conventional configuration. It is believed that this work could significantly lead an OFCS not only to the developments of a multiplexing current sensor system, but also to a long-distance remote monitoring of HV-lines because of both the geometric feasibility of fiber optic mechanism of the MRRI and the effectively demodulated circuit reduction of the PDS.

Optical time domain reflectometer (OTDR) is a very effective technique for distributed fiber sensing, in spite of its disadvantages including low spatial resolution, high cost and relatively noisy return. In order to improve the performance of OTDR, the concept of wavelet transform is introduced into OTDR in this paper. Wavelet transform is used to transform analysis from the time domain to the time- frequency domain, so not only the location of measurand can be detected more exactly, but also the character of frequency of the measurand can be analyzed. It has a wide use in distributed fiber sensors such as pressure, temperature, especially disturbance detection of one or more different physical measurand fiber sensor. In this paper, first the basic concept of OTDR is introduced and the fiber loss along the length of fiber is also analyzed. Second the principle of wavelet theory is described, it suggest that wavelet transform has a perfect character of localization and also a satisfying performance in the transient signal detection and signal decomposition from noisy background. At last results of analysis and experiment of wavelet transform in OTDR are presented by data and graph. The conclusion is that signals which is difficult to be analyzed and recognized in time or frequency domain can have a better resolution in time-frequency domain, it is important not only to backscattered OTDR but also other distributed fiber sensors.

This paper introduces a new type of optical electric field sensor which is used to detect high voltage and electric field and describes the principle and design of the sensor. The relation among electric field strength, modulation depth and linearity is established. Test results are also shown in the paper.

The report describes a 220kV Active Optical Fiber Voltage Transformer (AOVT). The transformer is different from the passive optical fiber voltage transformer, for no optical crystal is used in the 220kV AOVT. Its principle is that a low voltage is divided for the 220kV high voltage by a capacitive divider and then is converted into a digital signal. The optical fiber is used to transfer the measured digital signal and control signal. The 220kV AOVT consists of an outdoors-high voltage measurement unit and an indoors low voltage metering and controlling unit. The optical fiber connects these units. The low voltage is effectively isolated from the high voltage by means of the optical fiber and a special power supply method which is specially designed for the outdoor high voltage unit. As a result, the safe protection is reliable for the indoor low voltage equipment and the operation staff. Compared to the conventional voltage transformer, the advantages of the 220kV AOVT are high accuracy, low cost, excellent dynamic characteristics and immunity from electromagnetic interference. The 220kV AOVT has been tested, and its accuracy could achieve +/- 0.2 percent.