The feasibility of producing a practical buried fiber optic sensor with high sensitivity for detecting intruders is demonstrated. Experiments were carried out on such an all fiber Michelson interferometer in which the sensing arm was buried in sand. When a 42 inch sensing arm was buried 8 inches deep in sand, the weight required for a half fringe shift in the sensor output was 22 pounds and the sensitivity was about 10 degrees/pound. The relation between the applied pressure and the phase change was linear. Experimental results indicated that the sensitivity of an optical fiber sensor was sufficient to detect people on foot and vehicles passing over the buried fiber.

A distributed temperature sensor based on Raman scattering in optical fibers has been tested for use as coolant loop monitor in nuclear power plants. Different types of pure- silica-core, polyimide-coated fibers have been subjected to ⁶⁰Co-gamma-ray and fission-reactor irradiation at varying temperatures. ⁶⁰Co-gamma-ray irradiations at dose rates from 4.8 kR/h up to 1 MR/h were done. Simultaneous gamma-ray and high temperature experiments up to 300 degrees Celsius have also been performed. The induced loss of the tested fibers was found to saturate with increasing dose at the anti-Stokes and Stokes wavelengths. This feature was then made use of to develop a model for radiation induced loss which was used to make system lifetime predictions. It has also been demonstrated that the induced loss of the optical fibers is favorably affected by high-temperature use. A 10-fold decrease in the radiation- induced loss levels when the system was operated at 300 degrees Celsius was observed, as compared with room- temperature operation. The experiments have shown that with a pure-silica-core, polyimide-coated fiber the temperature sensing capabilities of the RDTS will not be degraded excessively if used at primary coolant loops with an expected upper radiation level of 200 R/hr.

This paper reports on the feasibility of monitoring the cure of an epoxy-amine resin system using a transmission-based optical fiber sensor and near-infrared spectroscopy. The sensor was prepared from two silica fibers aligned within a notched precision bore capillary tube to produce a robust transmission cell without the need for complicated alignment. The resin system used consisted of Shell Epikote 828 (resin) and 1,6-hexanediamine (hardener). Using the optical fiber sensor, spectra were collected throughout the cure over the wavelength range 1450 - 1700 nm. Cure data from the optical fiber sensor were compared with Fourier transform infrared spectroscopy (FTIR) experiments carried out at similar cure temperatures. The cure kinetic data were generated as a function of temperature for stoichiometric mixtures of the resin and hardener. An attempt was made to fit the cure data from the above mentioned techniques to a semi-empirical model. Good correlation was obtained between the cure model and the optical fiber cure data.

A novel reflectometric birefringent fiber remote strain sensor is reported. The sensor employs the principle of frequency modulation continuous wave interferometry and consists of a single length of single-mode birefringent fiber. The sensor is shown to have several advantages including a resolution of 2 microstrain resolution, a dynamic measurement range of 5000 microstrain, an environment-insensitive lead-in/lead-out signal section and a variable length strain sensing probe. The system is ideally suited to the measurement of absolute and relative strain.

A practical birefringent fiber Sagnac ring force sensor has been demonstrated. The sensor is based on the frequency modulation continuous wave technique and simply consists of a birefringent fiber ring. The intensity and the location of a stress applied to the fiber can be determined simultaneously by detecting the amplitude and the frequency of the beat signal which is produced by two forward-coupled mode beams in the Sagnac ring as a result of the applied stress. Similarly, the strain variation of one section of the fiber ring can also be measured by analyzing the phase shift of this beat signal. The experiments demonstrate that resolutions of 1 meter for distributed stress measurements and 4 microstrains for strain measurements can be obtained with this sensor system.

We present a dynamic scheme north finder using a low accuracy fiber optic gyroscope which the random walk noise is around 1.5 deg/h/(root)Hz. North finder accuracy has been estimated and experimental data also are presented and error sources are discussed. Two lock-in-amplifier algorithm is proposed for signal processing.

Chemical dye immobilization is very commonly used for optical fiber chemical sensors development. The dye may behave differently in aqueous state and in immobilized state. This paper describes the experimental results on absorption, emission and pH response of chemical indicator sodium fluorescein, both as dissolved in water and immobilized in sol-gel thin film, for optical fiber pH sensors development. It was found that in the sol-gel immobilized state, by altering the dye concentration and excitation/emission wavelength, a wide range of measurements from pH 0.5 to pH 10 is possible.

A distributed optical fiber pH sensor based on time resolved fluorescence is investigated. Fluorescein sodium was chosen as a pH indicator for this work because of its well known properties and high fluorescent intensity. A low temperature sol-gel glass manufacturing process was utilized to immobilize the indicator onto the optical fiber core. Thin (approximately 1 micrometer) porus glass films were deposited on the surface of the optical fiber core with indicator molecules entrapped in the matrix. An OTDR technique was employed to obtain the signal at specific positions along the fiber. A dye laser, pumped by a N₂ laser, produced 1 ns light pulses at 490 nm which were launched into a 1 by 2 optical fiber coupler. A 100 meter fiber with eight sensor sites was spliced to the coupler. The indicator molecules were excited via the evanescent wave. Part of the fluorescent emission from the indicator molecules was coupled back into the fiber and transmitted back to the coupler. A fast PMT tube was attached to the other arm of the 1 by 2 coupler to detect the fluorescent light. Results were obtained for solutions of various pH value in the range 6 - 12. The system appears to have potential for applications in environmental and safety monitoring.

The sensitivity of an extrinsic fiber-optic magnetic field detector which uses a gallium doped yttrium iron garnet bulk optic crystal as the sensing medium has been significantly improved by incorporating the sensor head in Fabry-Perot cavity.

Recent research on passive and active resonator fiber optic gyros are discussed. Basic research on the noise factors and the countermeasures in the R-FOG have been accumulated. The research to reduce the size of the system has also been carried out. System configurations of the B-FOG as well as the characteristics of the fiber Brillouin ring laser have been investigated. The B-FOG has the possibility to realize wide dynamic range with a simple configuration.

Significant progress has been made in recent years in multiplexing techniques for in-fiber Bragg grating (FBG) sensors. This paper is intended to give a systematic overview of recent progress in the multiplexing techniques, including wavelength-division-multiplexing, spatial- division-multiplexing, time-division-multiplexing, and their combinations. There is no doubt that these multiplexing techniques will play an important role in the FBG sensor technology as they make FBG sensor systems cost-effective for quasi-distributed measurement.

Advances in fiber optic sensors and, in particular, the technique of electropolymerization have led to a development which allows for porphyrins, the sensing molecules, to be attached directly onto the tip of an optical fiber. The sensing element as a whole is very robust, since during the process of electropolymerization the molecule forms a matrix on the surface of the fiber-film, thus ensuring no leeching of the film constituents to the surrounding environment. Luminescence lifetime decays were obtained using a novel dedicated instrumentation system. The data was analyzed using high level languages incorporating mathematical modeling capabilities. The results of this work are reported as well as a detailed discussion of the electropolymerization process with respect to the porphyrins.

An optical fibre Bragg grating (FBG) sensor was surface mounted onto a carbon fibre reinforced epoxy composite and subjected to static and dynamic loading. The FBG sensor was found to operate satisfactorily up to 700,000 cycles when the fatigue test was terminated. The fatigue test was conducted at a peak stress of 210 MPa and a stress ratio of -0.5. The FBG sensor was also found to operate satisfactorily over the cyclic loading frequency range of 0.1 - 6 Hz used in this study. The feasibility of using the sensor system for monitoring the stiffness ofthe composite during the fatigue test was demonstrated. The signal processing for the sensor system was based on a CCD spectrometer. The sensitivity of the static strain measurements was found to be approximately 80 jtc. A broadening ofthe FBG reflective spectrum was seen to develop as a function of fatigue cycles, and this phenomenon may be due to the delamination ofthe sensor from the surface ofthe composite.

We report the noise limitation of fiber optic gas sensors using laser sources. Interference between signal wave and reflected waves causes signal fluctuation in the output which limits the performance of the sensing system. Sensor resolution limited by these factors is calculated and compared with experimental results.

A novel interferometric detection scheme for measuring wavelength shift in an optical sensing system is described. In this scheme, in addition to the source wavelength to be measured, a further reference wavelength is employed to stabilize the optical path difference of the interferometer. This is designed to make the wavelength detection system insensitive to environment disturbances such as temperature fluctuation and mechanical vibration, and using this scheme a signal-to-noise ratio improvement of 25 db has been demonstrated.

The phase measurement error in an interferometric wavelength shift measurement scheme, such as that used in association with in-fiber Bragg grating sensors, has been investigated experimentally, with appropriate underpinning analytical theory. It has been shown that when a lock-in amplifier is employed to detect the phase shift generated by the Bragg wavelength shift, a pseudo-periodical measurement error can be introduced due to the difference between the amplitude of the optical path difference ramp and the value of Bragg wavelength. If the initial ramp deviation equals 20 nm, the measurement error may be as large as 5% of the total measurement range. By using a double-phase lock-in amplifier approach to measure the AC strain, the measurement error can be decreased to 0.4% of the total measurement range. By using the real-time measured period which corresponds to the Bragg wavelength with the distorted carrier signal of the interferometer as the reference period of a digital lock-in amplifier, the effect of the initial ramp deviation can be principally avoided, and the measurement error can be kept to an acceptably low level, about 0.1% of the total measurement range.

Modulator based on the amorphous Si-Te acousto-optic cell and operating in the mid-IR region has been manufactured and tested using 3.3 micrometer diode laser based on InGaAsSb/InAsSbP double heterostructure. Amplitude modulation efficiency for the laser beam coming from the end of a As₂S₃ fiber appeared to be not less than 70% allowing to use the cell in optical gas sensor applications. Methane gas fiber optic sensing was demonstrated using temperature tuning of the laser diode emission in the 3.28 - 3.34 micrometer range.

We report here the adaptation of an existing optical respiration monitor, the fiber optic respiratory plethysmograph (FORP), to act as a gating tool to compensate for respiratory motion that occurs during scans in magnetic resonance (MR) scanners. The instrument is based on the principle of bending losses in optical fibers, and features a user-friendly graphical interface written in Visual Basic for Windows. One of the novelties of the system is the use of an optical feedback channel to instruct the subject to inhale, exhale or hold their breath. Results are presented that demonstrate that the instrument is useful in helping a test subject reproduce accurate breath holds.

A computer-adapted fiber-optic temperature sensing system has been developed which aims to study both the theoretical aspect of fiber temperature sensing and the experimental aspect of such system. The system consists of a laser source, a fiber sensing element, an electronic fringes counting device, and an on-line personal computer. The temperature measurement is achieved by the conventional double beam fringe counting method with optical path length changes in the sensing beam due to the fiber expansion. The system can automatically measure the temperature changes in a sensing fiber arm which provides an insight of the heat generation and dissipation of the measured system. Unlike the conventional measuring devices such as thermocouples or solid state temperature sensors, the fiber sensor can easily be wrapped and shaped to fit the surface of the measuring object or even inside a molded plastic parts such as a computer case, which gives much more flexibility and applicability to the analysis of heat generation and dissipation in the operation of these machine parts. The reference beam is being set up on a temperature controlled optical bench to facilitate high sensitivity and high temperature resolution. The measuring beam has a motorized beam selection device for multiple fiber beam measurement. The project has been demonstrated in the laboratory and the system sensitivity and resolution are found to be as high as 0.01 degree Celsius. It is expected the system will find its application in many design studies which require thermal budgeting.

This paper reports on the use of a multimode extrinsic fiber Fabry-Perot interferometric sensor for quasi-static and dynamic fatigue loading experiments. A surface mounted extensometer was also used to measure the strain in the composite as a function of applied load. Excellent correlation was obtained between the strain data from the extensometer and the embedded EFPI sensor. With reference to dynamic loading, the sensor was found function reliable up to 1,600,000 cycles when the fatigue test was terminated. The fatigue tests were carried out using a peak stress of 260 MPa with a stress ratio of negative 0.40, and a frequency of 5 Hz. The signal processing technique was based on a channelled spectrum CCD spectrometer. The sensitivity of quasi-static strain measurements was approximately 30 micro-strain with a strain range of approximately negative 1% to 1%. The feasibility of using the EFPI sensor for stiffness-decay measurements during fatigue testing of composites was demonstrated. Preliminary results form the use of a single-mode EFPI sensor design for strain measurements in composites is also presented.

This paper presents a general overview of intensity-based optical fiber sensor systems, including those developed at Brunel University for condition and health monitoring of engineering materials. The sensor systems covered are: crack detection, a novel technique for converting glass reinforcing fibers into light guides for sensing applications, vibration monitoring and a new intensity- independent demodulation technique for fiber Fabry-Perot interferometers.

In many concrete bridges, the deformations are the most relevant parameter to be monitored in both short and long- terms. Strain monitoring gives only local information about the material behavior and too many such sensors would therefore be necessary to gain a complete understanding of the bridge behavior. We have found that fiber optic deformation sensors, with measurement bases of the order of one to a few meters, can give useful information both during the first days after concrete pouring and in the long term. In a first phase it is possible to monitor the thermal expansion due to the exothermic setting reaction and successively the thermal and drying shrinkages. Thanks to the long sensor basis, the detection of a crack traverse to the measurement region becomes probable and the evolution of cracks can therefore be followed with a reduced number of sensors. In the long-term it is possible to measure the geometric deformations and therefore the creeping of the bridge under static loads, especially under its own weight. In the past two years, our laboratory has installed hundreds of fiber optic deformation sensors in more than five concrete, composite steel-concrete, refurbished and enlarged bridges (road, highway and railway bridges). The measuring technique relies on low-coherence interferometry and offers a resolution down to a few microns even for long-term measurements. This contribution briefly discusses the measurement technique and then focuses on the development of a reliable sensor for direct concrete embedding and on the experimental results obtained on these bridges.

A computer-controlled optical fiber sensor system has been developed for the characterization of ultrasonic transducers in the megahertz range. The sensing element used is a short length of highly birefringent optical fiber. When an ultrasonic wave is incident normally upon the fiber, the birefringence, or the phase difference between the two polarized light waves in the fiber, is modulated. The phase modulation is converted into an intensity-modulated signal by means of polarimetry. To optimize and stabilize the signal against environmental effects such as temperature variations, a liquid-crystal phase retarder, controlled by feedback electronics, is placed in the optical path. Intensity noises arising from the laser source and the fiber leads are also eliminated by using signal processing techniques. The spatial intensity profile of an ultrasonic beam can be determined by scanning the sensing fiber across the ultrasonic beam. Fiber scanning and data acquisition are controlled by a personal computer. In this paper, the principle and the implementation of the sensor system are described. Experimental results obtained from characterizing commercial ultrasonic transducers are presented.

A Bragg wavelength shift of about 0.038 nm/degree Celsius was measured for fiber gratings centered around 1550 nm for a temperature range of 0 degrees Celsius to 120 degrees Celsius. This represents an improvement in temperature sensitivity that is 3.2 times than that could be achieved with a bare fiber grating and enables the design of more sensitive temperature sensors.

We present the performance of a sensor with an optical fiber strain gauge. The system adopts a phase-shifting technique with an equal phase shifting modulation to determine the strain on the sensor. It is accomplished by applying a triangle-wave-modulated signal to the injection current of a visible laser diode with precision temperature control, and its demodulation technique employs a digital signal processing (DSP) to calculate the phase of strain and a statistic processing to improve the signal-to-noise ratio. The experiments show that the relation between the optical phase difference and the external strain is linear.

The possibility for using the Faraday magneto-optic effect in direct-current (dc) measurement has not been extensively studied so far. However, the demand for dc measurement in industry is rising. It is valuable to investigate the design problems of such devices. This paper presents the design of a low-cost optical-fiber direct current measurement device in a specific application which requires a measurement range from 2 KA to 20 KA for a bus bar in a particular geometry and an accuracy of plus or minus 10% of full measurement scale. An experimental device had a measured performance of nearly plus or minus 6% accuracy of full scale and a dynamic range of 2 KA to 20 KA. The dynamic range can be increased while retaining an error current of approximately plus or minus 1.2 KA.

The paper covers the description of a fiber optic sensor of linear displacement with a single multimode fiber and a movement mirror positioned near the output end of the fiber perpendicularly to its axis. The value of the signal of the considered sensor is determined by the rate of a beam reflected from mirror and introduced back into the fiber. New methods of increase in the band of measured shifts and enhancement of the sensor sensitivity are described in the paper. In particular, we propose to fill a space between the fiber face and the mirror by the light-absorbing liquid and to use polarization splitting of input and output beams. Mathematical descriptions of the sensitive element and the polarization beam splitting scheme are considered in the paper. We used a method of geometrical optics in Hamiltonian formulation for mathematical sensor modeling. Presented experimental results confirm the theoretical conclusion.

The multimode fiber is one of the important components in optical imaging and multichannel sensing systems. The critical issue in the design of such systems is the level of the crosstalk ratio (light leakage between adjacent fibers or interchannels). The system performance degrades whenever crosstalk leads to a transfer of power from one fiber to another (or one channel from another). This paper develops a unique approach to derive and compute the crosstalk ratio, effective coupling coefficient and field distribution of flexible multimode fibers. Our results also demonstrate that Gaussian approximation can be used to compute the crosstalk ratio successfully. Furthermore, by taking advantage of the Gaussian approximation, we can obtain quantitative correlation between the crosstalk ratio and fiber parameters in order to reduce crosstalk. This may lead to improved contrast and sensitivity of fiber imaging and multichannel sensing systems.

The distributed optical fiber Raman photon temperature sensor (DOFRPTS) system is a new sensor system, use it for the measurement of temperature field in space on time. In this system, the spontaneous Raman photons is temperature signal's carrier, the optical fiber is transmitted medium, also is sensitive medium. The signal analysis of the DOFRPTS system has been discussed in this paper.

In this paper we present an optical scanning, fiber dual- extrinsic Fabry-Perot interferometer (DEFPI) system for measuring small distance absolutely. Taking the scanning wavelength as an 'inter-converter' to compare the gap length of the sensing head with a reference length, we may obtain, in practice, a semi-absolute measurement of the sensing head length. The measurement is independent from the wavelength scanning accuracy and the reference cavity length can be self-calibrated simply by changing the sensing length with a known distance.

Standard of technology of a number of works, as for example in production of microelectronics elements, is defined to a considerable extent by the degree of purity of acids, solvents, photoresist which are used. Concentration of the microparticles in process mediums has to be in range from 100 to 1000 particles per I. That is why particular attention is given for working out of methods and devices for checking the purity of liquid mediums. There is reported briefly about the devices, developed at Applied Physics Institute of Lviv Ivan Franko State University, which main principle of functioning is based on analyzing of light scattered by microparticles suspended in researched liquid in ranges of Mi-theory. Developed complex of the devices can be united in monitoring system intended for control of the content of microparticles in liquid mediums used in certain processes.

A new hybrid current sensor is described in this paper. The sensor uses a conventional current transformer to sense the electric current flowing in the conductor at high potential and converts this signal to an optical phase change in a novel differentiating optic fiber Mach-Zehnder interferometer. The optical signal is then transmitted to ground potential for subsequent processing. By using the technique, a resolution of 0.5 A/(root)Hz and an accuracy of plus or minus 0.7% are obtained at the line frequency of 50 Hz and the dynamic range is 1.58 to approximately 380 A in our prototype architecture.

Today little is known about the behavior of particles in solid-gas two-phase flow due to the lack of suitable measuring methods. In this paper, a new equipment based on optical fiber sensor technology is developed to measure the particle velocity and concentration. The measured results in a gas fluidized bed of 50 cm in four sides and 4.2 m in bed height are shown. This equipment consists of three main parts, the optical fiber sensor, the signal converter and amplifier and the data process system. The sensor is made of a bundle of fine optical fibers and is designed to measure the flow velocity, flow direction and the concentration, on the basis of the light correlation method for flow velocity and light scattering method for concentration. This equipment has 4 kinds of sample rates (1 MHz, 0.5 MHz, 0.25 MHz and 0.125 MHz) so the particle velocities from 0.5 to 25 m/s can be measured by use of different sample rates. The concentration ranges from 0.1 to 20 kg/m³. It has been confirmed that the measuring precision is about plus or minus 3% and plus or minus 5% for the flow velocity and concentration, respectively.

Through the years a number of different optical systems for high voltage applications have been presented. The main field of interest has been devices replacing conventional current/voltage transformers utilizing the non-conductive nature of the optical components. The aim of the reported work was to develop an optical current transducer (OCT) based on the Faraday effect using bulk glass as the sensing element for high voltage applications. An OCT has been developed for utilization in 110 kV substation. A light beam circulates the electric conductor once and returns once. The optical path in the sensing element was designed approximately completely close. Therefore, the effect of the magnetic field, generated by other conductors adjacent to the conductor where the current to be measured was applied, can be eliminated to a high degree. Special attention is also put on the design of the signal processing system. A data acquisition and signal processing system with excellent linearity and high accuracy has been configured. The operating results show that the OCT is satisfactory under common conditions, whose accuracy is I multiplied by 0.2% plus or minus 0.1 A. Further efforts will be made to improve the OCT's stability. The sensor design, the signal processing system and the testing results are described in this paper. The system errors are analyzed.

A conical microlens tipped on the SMF (single mode fiber) endface is evaluated for coupling between DFB laser diode and single-mode fibers. A theoretical model, based on coupling mode theory and Gaussian mode shapes for the laser and fiber fields, is developed to predict the coupling performance of this microlens. The coupling efficiency is calculated nearly 90% theoretically and measured at best to be 73.9%. A new equipment for fabricating the conical microlens is designed, which has the advantage of low-cost, simple manipulation, high finished product rate.

Fiber-optic evanescent wave sensor which consists of two D- fibers is analyzed by vectorial finite element method (VFEM) in this paper. Spurious solutions are eliminated out of the region of effective modes by the penalty variation principle. Utilizing mode coupling theory and choosing a large number of finite elements with a number of nodes N equals 1048, several important results for designing the fiber-optic evanescent wave in sensing region is obtained. The relative parameters, including the interval and distance of coupling region, the radii and refractive indices of the D-shape fibers, and the characteristics of sensing medium, are derived. Consequently, the contour map of those parameters is presented, and for a certain medium in sensing region, it is convenient to design an optimal contribution of those parameters.

In the paper, we gave a phase contrast method to measure the birefringent axis orientation in polarization-maintaining fiber (PMF) with matching refractive-index (MRI). The phase contrast intensity profiles in PANDA fiber and distinguishing characteristics were obtained by image analysis of side view image systems. Experiments and computer simulation showed that the difference between two crests of intensity profile was not only used for determining angular orientation but also for determining the direction of rotation. The angular resolution of orientation was less than 2 degrees in phase contrast method. The difference between geometric and birefringent axes in PMF would be the limit of accuracy in side view image system.

White-light interferometry (WLI) is a powerful technique for distributed fiber-optic sensing system. The sensing regions are determined by the optical path difference between two polarization modes of dual-mode optical fiber and the coupling coefficients are measured by detecting the interferogram. However, the performance of the system is limited by the coherent length of low-coherent source and the crosstalk among the sensing units. In this paper, we propose a method to process interferogram to improve resolution and eliminate crosstalk in distributed sensing system.

A novel fiber-optic pressure sensor with reflecting optical structure for the simultaneous measurement of temperature is presented. The operation principle of the sensor is based on the photoelastic effect and the temperature signal is extracted from the fluctuation of the quasi working point of the sensor due to the thermal effect of the wave plate. The wave plate used here is not the 1/4 lambda as used in typical photoelastic pressure sensors in order to obtain the best response of linearity. Two kinds of bridge compensation techniques are used for the pressure and the temperature respectively. The experimental results show that once the temperature is determined, the fluctuation of the pressure output can be eliminated, and more accurate pressure meter is available.

White-light source synthesis technique has been demonstrated in a 1.3 micrometer all-fiber Michelson interferometer for the first time to our knowledge. The optimal wavelengths of the two sources are 1.3 micrometer and 1.55 micrometer, respectively. The minimum signal to noise ratio required by the system SNR_min has been reduced by 35 dB in theory and 19 dB in experiment. With the source synthesis technique, the all-fiber interferometer has an improved measurement accuracy based on interference packet modulation and an enhanced stability suitable for in situ application.

A sensor using a single monomode low-birefringence (Lo-Bi) fiber for simultaneous measurement of current and voltage has been designed, which uses Faraday effect for detection of current and Kerr effect for detection of voltage. Theoretical analysis proved the current component can be measured free from the influence of the voltage component, and the two components can be easily separated. Experimental results demonstrate the feasibility of the Kerr effect of the Lo-Bi fiber for sensing voltage, which is the main point in this proposal.

We report here the experimentation of an embedded fiber optic sensor applied on cure monitor and strain measurement of composite materials. This sensor using twisted standard communication gradient optical fibers utilizes the optical loss due to fiber microbending dependance on the internal strain on composites. The choices of optical fibers and parameters of this kind of sensors are discussed in this paper. Recently there has been an international interest in embedding optic fiber sensors in composite materials to monitor the cure process and measure the strain and damage. Many ways have been used, such as the methods of interference, grating, polarization and intensity, etc. Our purpose is to select a simple and inexpensive method. So under the present conditions of our experimental house, we have embedded twisted standard communication multi-modes gradient optical fibers in composite materials and made altogether studies of the cure, the strain and the damage. Satisfied results have been obtained and the method is worthy of further research.

This paper reports authors' works on design of an optical fiber sensor which can in situ monitor and analyze the concentration and composition of pharmaceutical in blood. An optical probe is inserted in blood vessels, ultraviolet light is coupled into one branch of Y-type optical fiber to induce fluorescence emitting from the pharmaceutical in blood. The fluorescence is collected by another branch of Y optical fiber and detected by photomultiplier. The detected signal is sampled into computer which can process the data in realtime and display dynamically the fluorescence spectrum on the screen. Compared with ordinary analytical instruments such as various spectrometer and chromatographs, this sensor has the advantages that it can measure in situ and thus omit the process of extracting serum or plasma from blood and reduce the detecting time. This advantage has practical value in clinical diagnosis. In this research, the major difficulty is that the blood is not transparent. Authors apply a membrane adhered to the top of the probe and frustrating the access of hemocytes thus the fluorescence can be collected. This sensor can measure the concentration of pharmaceutical in blood in the grade of micrograms/milliliter.

In this paper, we have proposed a novel wavelength scanning fiber-optic interferometer for absolute distance measurement. A wavelength scanning source is used to simultaneously illuminate two F-P cavities, one as a sensing interferometer, the other as reference interferometer. With this method, we can obtain absolute measurement, and decrease the demands on the light source, such as its stability of wavelength and power, its repeatability of scanning range. The accuracy of 0.2 micrometer and resolution of 0.04 micrometer are achieved, in the range of 0 - 2 mm.

A practical TDM (time division multiplex) fiber sensor network is presented in this paper, which has been applied to measure liquid level, interface and temperature of gasoline. The topology structure of the network has been designed carefully to save the fiber cable, light sources and detectors. The most important components in this network are couplers and fiber delayers, which achieved the distribution of light power and the separation of light signal, respectively. By arranging these components rationally, we have finished a system involving thirty sensors, array of couplers, one light source and one detector. In this paper we describe the time-division theory of the network and calculate the maximum content of fiber sensors by analyzing the loss of power in detail. At the same time, the stability and the reliability of the network also are discussed in detail. As a result, we get the precision of 2 mm, 5 mm and 0.2 degrees Celsius for level, interface and temperature, respectively.

In this paper an exploratory study of fiber optic nuclear radiation sensor focus on nuclear log in oil industry is presented. The principle and structure of a prototype fiber optic nuclear radiation sensor (mainly measuring gamma ray) based on the principle of radiation-induced loss are discussed. Its great advantages over conventional nuclear radiation sensors are described as well. The experiment results about radiation-induced losses of different doped concentration of PbO in sensitive fibers are presented and analyzed. The experiment results and analyses show that this kind of fiber optic nuclear radiation sensor has a vast range of prospects not only in nuclear log but in other nuclear radiation detecting application fields.

Optical current transformer (OCT) has been sought for the past two decades but has not been realized satisfactorily because of the problems in the long term field use of the polarization-preserving optical fibers which are required in the sensors based on the traditional principles such as Faraday rotation, etc. Based on fiber technology and a new physical effect reported, the diffraction angle of a laser beam focused on the ferrofluid thin film being approximately proportional to the field H² (in turn to the current I²) and being independent of the polarization state of the light, a new optical current sensor was designed and tested. When set 1 cm away from the electric power line, the current resolution of the sensor is 1 A and the measuring range is 0 A to 10² A, extendable to 2 multiplied by 10³ A when set 20 cm away from the line. The temperature dependence of the diffraction angle was measured to be proportional to T^-2 in the temperature range from minus 30 degrees Celsius to plus 50 degrees Celsius.

In this paper, we present a new kind of way to produce the fiber Bragg grating, in which a Fresnel prism is used as an interferometer. Comparing with the traditional holograph interferometer, the new method involves a lot of advantages. Based on the grating we have made with this method, we set up a sensor system to research its temperature characteristic. In order to increase the ratio of signal to noise, a tunable extra-cavity semiconductor laser is used as a light source instead of traditional wide-band source. The result of temperature has also been present in this paper, from which the sensitivity coefficient can be gotten.

An intrinsic fiber-optic strain sensor for the health monitoring in civil engineering is described. The results of the application of the sensor to the steel tension and concrete compression which were compared with strain gauge showed good linearity, and can be used to reflect correctly the magnitude of the loads upon the steel or the concrete structure. The size of this kind of the sensor is small. The technique of fixing the sensor is briefly discussed. The sensor is convenient for the application because the sensor protected by glue can be easily attached to the surface of the specimen and no other special method is desired.

This paper describes an acoustic strain effect of a multimode optic-fiber sensor. The transmitted coherent light wave through a multimode fiber produces a complex speckle pattern. This pattern is analyzed with the method of modal interference. The speckle pattern changes with the acoustic phase modulation of the modes. The light intensity has been measured. An experimental system of this sensor has been built up. The spectrum of the acoustic effect has been obtained.

A new constructed fiber thermometer probe using fluorescent decay is presented. The fluorescent material in the probe is substituted for by using a compact sapphire fiber, in which the end part is doped with some fluorescent dopant. The sapphire fiber is coupled with the normal silica fiber for signal transmission. Because the sapphire fiber is of enough length, the coupling can be made at a place away from the severe environment. Then the performance of the probe can be assured by the excellent physical properties of the sapphire fiber if only the doped end is ideally combined with the fiber itself. The sapphire fiber with Cr³⁺ doping in the end was grown using laser heated pedestal growth (LHPG) apparatus. Two kinds of doping methods were compared to achieve an ideally combined sapphire fiber. Using a high bright green LED as the stimulating light source, the fluorescence of the fiber with only end doped was measured using an optical multi-channel analyzer. The fluorescence at the wavelength of 694 nm can be clearly detected. Temperature dependance of the fluorescent decay is being determined between the temperature of 20 to 450 degrees Celsius, on which the temperature can be measured.

This paper reports the development of a sapphire ((alpha) - Al₂O₃) single crystal optical fiber thermometer using two wavelength bands. A thin film of precious metal or ceramic deposited onto one end of the sapphire fiber forms a mini-radiation cavity. The other end of the sapphire fiber is coupled to a low-loss silica fiber. Radiation from the small cavity is transmitted along the silica fiber into a photodetection system which consists of a lens, beam splitter, two interference filters (820 nm and 940 nm center wavelength, 30 nm bandwidth) and two silicon photocells. The temperature measurement is based on the detection of radiation from the small cavity. The sapphire fiber (0.25 - 1.0 mm diameter, 100 - 450 mm length) was grown by the laser heated pedestal growth (LHPG) methods. Transmission loss in the sapphire fiber was experimentally measured. Theoretical analysis shows the apparent emittance of the small cavity with a length to diameter (L/D) ratio greater than eight is a constant value near to one, so the small cavity can be considered as a small black-body cavity. Using the developed sapphire fiber temperature sensor, we have built a sapphire fiber thermometer based on a 8098 single-chip microcomputer system. It was calibrated at some known stable temperature point and uses the fundamental radiation law to extrapolate to other temperatures. By taking the ratio of the optical power at two wavelengths, errors due to changes in the system, such as emissivity and transmission losses, can be canceled out. The thermometer has an operating temperature range of 800 to 1900 degrees Celsius, and an accuracy of 0.2% at 1000 degrees Celsius. There are a number of applications of the thermometer both in science and industry.

A low fineness fiber optic Fabry-Perot interferometric displacement sensor has been developed and tested. With using a high performance He-Ne laser, low noise photodetectors, low drift operational amplifiers, 6-pole Butterworth filters and perfect digital signal processing circuits, a 0.005 nm displacement resolution is obtained.

Distributed fiber optic sensing for methane detection is put forward based on the characteristics of supported catalytic sensor (SCS) in this paper. By making use of the relationship between methane gas density (MGD) and SCS's working temperature, it is possible to convert the distribution detection of MGD to that of temperature. Initial experiment results prove that this method is feasible for the measurement of MGD distribution.

Based on the effects of mode-volume mismatch and lateral bending, a new type of optical fiber intensity sensors are presented. These sensors do not require the use of external structures to impose perturbations on fibers. Instead, the topological structures are formed directly onto the fiber cladding. The geometry of the features is defined by thermal engraving and the structures are formed by chemical etching. The etched fiber sensing elements have been fabricated with asymmetric structures and tested as strain sensors. It has been shown in experiment that the responses of the optical fiber strain gauges are linear, repeatable, have a high cyclic endurance and temperature stability and no measurable hysteresis. The etched fiberoptic sensing array embedded in composites and the principle and technology of array sensing signal processing in artificial neural network are also described.

A method which is theoretically and experimentally proved to have the ability of eliminating the micro-interference to the leading optical fiber in a bulk glass current sensor is presented here. The method is based on the fact that the polarization coupling is more sensitive to the environment than the intensity coupling is in an optical fiber. All of the two orthogonally polarized beams of the leading fiber are used in this method to improve the stability of the input light intensity.

An X-shape optical fiber pressure sensor has been proposed. The sensor is constituted by a single mode optical fiber directional coupler, at one output end of which a layer of Al-film is evaporated. The output fiber with Al-film covered end serves as a sensing element and self-reference arm as well, and the other to monitor the instability of light source. One of two input ends of the directional coupler acts as an input end of the sensor, another as an output end of the return light signal from the Al-covered output end of the coupler. In principle, the sensor is based on polarization interference caused by transverse pressure. From the normalized intensity of the output light beam and its rotation angle, the pressure can be determined, ranging from 0 to 120,000 dyne/cm.

Fiber Bragg grating (FBG) is produced in the core of a germania-doped fiber with a permanent periodic index modulation by specific techniques. Its intrinsic advantages over conventional fiber optic sensors makes FBG sensor an attractive candidate in smart structures. The center wavelength of the grating is sensitive to longitudinal strain. In this paper, we report our studies on FBG strain sensors. After giving a linear relationship between wavelength and strain, we demonstrate our experiments with FBGs to measure strain of a deformed aluminum cantilever by the use of an optical multichannel analyzer (OMA IV).

A theoretical and experimental study is conducted to investigate applicability of a single-mode fiber ultrasonic sensor for detecting the shock-wave in optical breakdown in air induced by a high power laser pulse. The sensor is based on the ultrasonically induced modal birefringence which alters the polarization state of the optical beam propagating through the fiber. The shock-wave signals have been gotten by using the sensor. It is shown that the single-mode fiber sensor has enough sensibility to detect shock-wave in air, but it is dependent on the fiber- ultrasonic interaction length and the intensity of shock- wave.

Beam instability is one important problem of one's interests. Many scientists make a lot of research work for overcoming it by different kinds of methods. Now we discuss it in another way for breaking fresh ground. First, we consider the bunched beam delta function instead of Gaussian distribution. Second, the one dimension process method is employed in analyzing the stability aperture suppressed by statistical filter, one new feedback control system is made up by optical fiber. It is a convenient model for developing a developed control mode in the future.

The sensor head of the high-temperature fiber optic sensor plays a very important role in the measurement, it directly determines the frequency response characteristics, distinguishability and other features of the sensor, so the detailed and advanced research is necessary. In this paper, the frequency response characteristics of high-temperature fiber optic sensor head are studied by means of a laser heated system, relationship between sensor head's response time and its geometrical sizes is obtained, which is in accord with theoretical evaluations.

For the detection of methane (CH₄) gas concentration in some mining complexes, the paper studies and discusses two kinds of easily-realized CH₄ gas opticfiber sensor, that is infrared absorption CH₄ gas optic fiber sensor and thin film transmission CH₄ gas optic fiber sensor. The optic structure of the sensor is discussed, and the paper compares the difference between the single optic structure system and the double one. It puts forward a multipoint long-distance detection system constructed by the micro- computer small system and the upper computer, and discusses the hardware and software system.

A kind of optical fiber sensor mainly used for the terminal winding vibration monitoring in electric generator is discussed. Within this sensor, the light from a LED passes through an optical fiber; the fiber end is mounted on a reflecting cantilever beam, which is sensitive to the vibration of the detected object; the reflected light coupled back through the same fiber is modulated by the vibration and detected by a photodetector. With signal processing, the vibration acceleration, velocity and displacement can be obtained. The cantilever beam, which is the key component of the sensor, is a micromechanical silicon structure. The bandwidth of the sensor is 10 - 1000 Hz, resolution 0.1 m/s², dynamic range 0 - 10 multiplied by 9.8 m/s², weight 15 grams, fiber length 1000 m. The result of the experiment in a real electric generator is proposed.

This paper describes the detailed information about how to design the strain diaphragm used in the microbend fiber- optic pressure sensor. The parameters of the diaphragms and the good tested results are also shown.

In this paper, a new method of liquid level measurement using discrete frequency IMCW ladar and optical fiber is described. The distance measurement is effectively made using the absolute technique of ladar in which the phase of an amplitude modulated light wave reflected from the liquid level is compared with that of the original modulation signal. To compensate the phase drift due to the change of delay time in electric circuit, a symmetry optical fiber is used as a reference path. The signal path and the reference path are measured in turn, and the difference between two paths is in proportion to the distance from the sensor head to the surface of the liquid. The optical unit is installed at a fixed reference point above the surface of liquid, and it connects with the electric unit by optical fibers. The main attributes of this system are that it neither requires electrical supplies or produces electrical signals in situ. It can be used in the oil industry due to the intrinsic safety. According to the test results, the accuracy of this system is better than 0.2%.

In this paper, a fiber optic pressure sensor system based on the photoelastic effect is described. By application of a new balanced bridge referencing technique, the sensor is satisfactorily loss-compensated. In order to improve the long-term stability of this system in practical use, a more stable and compact sensor head is realized. By theoretical analysis and experiment, the system error which is due to drifts in the wavelength of light source has been eliminated using software compensation. In order to compensate the system's time-drifting and temperature-drifting, pattern identification technique and adaptive filter are used. This system has been put into practical operation for oil storage and level measurement in tanks, and the long-term stability of the sensor is proved to be better than 0.2%. This work not only solves a practical problem of fiber optic pressure sensor, but also has a general significance to solve the problem of long-term drifts in intensity-modulated fiber optic sensor.

The theoretical analysis and design of a novel Faraday- effect current sensor are described in this paper. The new Faraday-effect current sensor consists of a spiral conductor carrying current and a Faraday-glass rod placed in the axis of the spiral conductor. Theoretical analysis and experimental research show that this scheme has advantages of easily controlled sensitivity and simple optic arrangement which make it a very suitable current sensor in the range below 500 A.

A new method to reduce the reflection-induced phase between the two orthogonal components of the linearly polarized light after the reflections is presented. The sensing head is introduced, and the result comparing to 'the critical angle head' is given.

In this paper, for optical fiber strain and temperature sensors, we discuss the relation between condition number and the solution of a set of linear equations about strain and temperature, develop the theoretical formulae to calculate the cross-sensitivity and quantitatively calculate the error induced by omitting cross-sensitivity for any values of strain and temperature and obtain some useful conclusions.

A self-calibrating fiber-optic level sensor system composed of a fiber-optic pressure sensor and two optical fiber level probes is described. The pressure sensor is based on the photoelastic effect and compensated with a method of optical bridge. The optic fiber probe is based on an optical intensity modulation method in which the reflected optical power by the probe sensitively depends on the refractive index of the surrounding medium. In the self-calibrating system two optical fiber probes are set at two heights of the oil tank, which are as two basic reference points The pressure sensor is connected to the bottom of the tank to measure the static pressure continuously. As the liquid level passing the reference point the probe gives out a signal to the computer to correct the measurement errors and recalibrate the sensor. The system has been applied to actual measurement in industry and the long term accuracy has reached to 0.2$% of full-scale.

A fiber optical ranging sensor used in laser proximity fuze is described in this paper. In the fuze, pulse laser diode (LD) is used as light source and trigger signal is generated by comparing the reflected light pulses with the reference pulses by a correlator after they were converted into electric signals by PIN photodiodes. Multi-mode fibers and integrated optical devices are used in the system so that the structure can be more compact. Optical fiber delay line is used to offer precise delay time for reference channel.

Plastic optical fibers (POFs) with 2 mm-diameter are arranged in a chest silhouette in 1:20 reduced scale as a sensor and a beam from a small He-Ne laser is used for shooting and aiming practices. The locations and times of hitting points can be repeated after shooting. Optical fiber simulator for shooting and aiming practices has many advantages such as small, light, safe, reliable, low-cost, convenient to use and no restriction of environment and area. It can be used by recruits for shooting and aiming practices and has been put into use in many troops.

In this paper the radiation low temperature measurement with the special optical quartz fiber bundle is researched. An end of the optical fiber bundle is circular, another end of the optical fiber bundle is rectangular, for the coupling efficiency between the optical fiber bundle and the target and between the optical fiber bundle and the detector is enhanced. The theory research demonstrates that the radiation power received and guided by the optical fiber bundle does not depend on the directly coupled distances, which makes this thermometer very convenient for using and calibrating. The temperature measurement range 150 degrees Celsius to 600 degrees Celsius is realized at present.

This is a report on a type of small-sized interferometer, which makes use of the coupling of optical fiber and gradient index lens (GRIN) to form a type of light path which radiates paralled light beams, optical filter is used to divide a beam into two, the interferometer is small-sized and highly sensitive, which can be used to measure the index of refraction of transparent gas and liquid.

It has developed and performed a novel fiberoptic immunosensor instrument with operating wavelength 400 - 760 nm and repeatability cv equals 0.27%. The instrument has many excellent features such as simplified operation, faster testing time, higher sensitivity and economic cost. It has completely eliminated recovery period which traditional immunosensor owned due to use separative sensor structure. It can widely apply to test for bacteria, virus, hormone, parasite and cancer protein in clinical examination. The instrument has operated in laboratory and relevant medicine units and successfully tested monoclonal rat-anti-human of 413 cases in clinic and prepared with existing ELISA method, the coincidence probability reached 94 to 100%.

A new type of optical fiber pressure sensor is introduced in this paper. The ratio measurement by means of the sensing optical fiber and the reference fiber with different beginning positions and the technique to improve the stability of the sensor are first discussed. Then the ability to restrain and compensate the interference of the same nature through the double channel ratio measurement is illustrated. Finally, the performance of sensor and its engineering design are discussed.

Fiber-optic sensors are maturing at a fast pace with multifunction integrated optics making many of these sensors practical. We first demonstrate hybrid integrated optical accelerometer system which combines the Ti:LiNbO₃ chip and the polarization-maintaining fiber to pick up vibration signal. So this system has both advantages of integrated optics and fiber-optic sensors. This paper summarizes of architecture of hybrid integrated optical accelerometer.

Integrated-optic technology can provide compact and rugged fiber-optic sensors. In this paper, we first propose and demonstrate an optical integrated circuits (IC) device in the Ti:LiNbO₃ for a fiber-optic accelerometer, including basic design concepts, fabrication techniques and waveguide components.

Interferometric fiber optic gyroscope (IFOG) has been analyzed with autocontrol theory in this paper. An open-loop IFOG system is not able to restrain the bias drift, but a closed-loop IFOG system can do it very well using negative feedback in order to suppress zero drift. The result of our theoretic analysis and computer simulation indicate that the bias drift of a closed-loop system is smaller than an open- loop one.

This paper describes a mixed fiber optical measuring system for the isolated phase busbar. As the magnetic field in the isolated phase busbar is only related to the busbar current, the current sensor, which makes up of the diamagnetic SF-6 glass with the thin-film polarizer and analyzer at both its ends, is placed inside the enclosed shell but outside the busbar, and the distance from the current sensor to the axis of the busbar depends upon the value of the current measured. The laboratorial experiment shows that the optical measuring system is reliable for using in the power system instead of the conventional current transformer.

A multi-mode fiber-optic accelerometer, based on intensity modulation, designed for vibration measurement in electrical machines is presented. The sensor shows an acceleration sensitivity of 2181 m/s²; range of frequency of 0 - 600 Hz; resolution of 0.01 g and linearity error of less than 5%. This accelerometer has already been used in 100,000 kW high power generator. The wave shape and frequency spectrum of the vibration of stator winding were recorded for the first time in China.

The advantage and disadvantage of the conventional detecting methods of electric or magnetic field sensing signal in the fiber optical sensing system are discussed. A new digital detecting method of electric or magnetic field sensing signal based on the optical modulation and electrical demodulation is proposed in order to eliminate the power frequency and low frequency noises. The digital detecting circuit is designed and the detecting software is developed. In design of the circuit, because the closed-loop synchronous sampling technique is used, not only the leakage effect is controlled and the detecting accuracy is increased, but also the signal processing is simplified, so it has better real-time characteristics. The experiments show that the test results detected by this method have good linearity.

In passive fiber optic components adhered by pure epoxy- adhesive, the coupling efficiency decreased by the maximum of 5.27 dB when temperature increased from 23 degrees Celsius to 100 degrees Celsius, but it only increased by less than 2 dB when temperature decreased from 100 degrees Celsius to 23 degrees Celsius. The coupling efficiency in 23 degrees Celsius differed by nearly 3 dB and the experiment curve was not coincident. When we doped 100 wt% of 200 mesh iron powder in pure epoxy-adhesive, the coupling efficiency was nearly unchanged with the maximum difference of 0.2 dB and the experiment curve was coincident in the course of temperature increasing from 23 degrees Celsius to 100 degrees Celsius and decreasing from 100 degrees Celsius to 23 degrees Celsius. This method improves greatly temperature stability of passive fiber optic components adhered by epoxy-adhesive and enhances effectively reliability of fiber optic sensors used in engineering applications.

The reflective intensity-modulated fiber optic sensor for measuring displacement, the antenna-shaped fiber optic sensor, is usually composed of a fiber bundle with the emitting and receiving fibers in a specific arrangement at the probe tip. The three elementary types of fiber arrangement are: concentric distribution, semicircular distribution and random distribution. In comparison with the size of the fiber optic sensor, the thickness of clad and binding element of the fibers is so small that it can be ignored. The mathematical models of the modulation function for the single fiber couple which is composed of both an emitting fiber and a receiving one have once been presented. Analyzing the distribution of the fibers inside the fiber optic sensor by using the geometric and statistical theories, the general mathematical models of modulation function for the three types of the sensors mentioned above have been proposed. And all the models are simulated with computer and all the simulating results are briefly analyzed.

The design principle, manufacture and technical parameters of optical fiber encoder with coded resin plate is reported in this paper. The resin plate has special superiority compared with glass plate. The resin plate can be adapted to use in vibrative environments (such as spaceflight and elevator and so on). The resin plate is lighter, so it has higher mechanical conversion efficiency. It can be made the super small size to be used in special space.

This paper discusses a real-time monitoring system using embedded fiber-optic sensors and the signal processing of the system. The etched fibers are embedded in composite material perpendicularly to build a two-dimensional fiber- sensor array. The output light signals, by a CCD (charge- coupled device), are converted into the electric signals which are transmitted to A/D (analog-digital) interface and are processed by a computer. So the state of the composite material can be real-time monitored from the monitor. This paper describes the interface sampling and software design and gives the detecting results.

This paper introduces the principle and the electron response characteristics of PSD, describes the structure feature of the new type MCP-PSD photon-counting tube. The following rules of the series working of MCP is expounded. Finally, the application prospect of the MCP-PSD devices have been pointed out.

Numerical aperture is an important parameter in design, manufacturing and application of optical fiber and optical fiber sensor. Numerical aperture of multimode fibers with curvature was rarely investigated. Fu Huaijie e. t. only concluded for numerical aperture of incoming ray on X_o equals 0, y_o equals 0 of optical fiber end surface. Actually, numerical aperture of different incoming point is different, because optical fiber cylindrical symmetrical character was destroyed, the concluded equation doesn't have universal significance. In this paper we derive the numerical aperture equation of bending plane ray, using scaler quality proximate theory and ray equation. We show our conclusion and discuss its significance.

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

It is significant to study and employ interferometric optical fiber sensors which are most sensitive to measurand and can be used to measure some critical parameters of measurands, it is, however, not practical because of the difficulties that lie in the aspect of interferometric signal demodulation, which may be overcome by several different ways extensively studied such as active homodyne phase detection, passive homodyne phase detection and heterodyne phase detection. Passive homodyne phase detection for interferometric sensors uses a passive optical element to provide optical pi/2 phase shift output, the measurand induced phase change is recovered by the detection electronics. A 3 multiplied by 3 directional coupler can be used to obtain the optical pi/2 phase shift output and hence to form interferometric optical sensor. In this article, fundamental principles of the sensor were analyzed using it, which possess characteristics of all-optical fiber, high- sensitivity, high-distinctiveness and easy integration, strain measurements were completed. The experimental results were given and also characteristics of the sensor were analyzed.

In this paper, a non-contact temperature measurement by calculating the decay time of the fluorescence is presented, it uses a phosphor powder material which is painted on the measured surface by mixing some resin, A new math process method is carried in to avoid the influence of dc drift.