Direct measurement of temperature in coal gasifiers requires a sensor technology that can withstand the extremely harsh environment posed by the high temperatures and corrosive agents present in these systems. An optical ultrahigh temperature measurement system is developed to address this critical need. This sensor is based on the broadband polarimetric differential interferometry (BPDI) sensing technology, in which optical spectrum is measured instead of direct detection of optical intensity. Resolution better than 0.1oC and high precision are achieved over a wide dynamic measurement range from room temperature up to 1600oC. This optical thermometer is immune to optical source power fluctuations and fiber losses. The other advantages of this thermometer are its simplicity, low-cost and long-term stability in harsh environments.

A fiber thermometer using the cross detection of the fluorescence decay and background radiation was presented to measure the temperature from room temperature to over 1600 °C. A YAG crystal fiber with a Tm doped tip was used as the sensing material. A phase-locked detection scheme was used for the fluorescence detection and background radiation compensation. The compensation current was also used for the background radiation detection. The fluorescence characteristics of the Tm doped YAG crystal fiber was analyzed in a temperature range from room temperature to over 1200 °C. The annealing effect on the probe material under high temperature was also investigated. The preliminary result showed that the system could achieve a resolution much better than 1 °C over the whole temperature range from room temperature to 1400 °C.

A sapphire fiber thermometer probe with Cr3+ ion doped tip end was grown from the laser heated pedestal growth method. The fiber probe offers advantages of compact construct, high performance and ability to withstand high temperature. The temperature dependence of fluorescence of the probe was investigated, and a sapphire fiber thermometer based on its fluorescent decay was presented. Among the detection rang from the room temperature to 450 c , the thermometer has an average temperature resolution of 10C.The thermometer may be used in microwave treatment and thermal monitoring of Medium Voltage substations.

Detection of mechanical vibration with a fiber Bragg grating (FBG) based on the intensity-modulation method provides us with simplicity and compactness of the sensor as well as high sensitivity, wide dynamic range and wide frequency response in sensing. The slope of the FBG transmittance or reflectance spectrum curve at the operation wavelength determines the sensitivity of the sensor. Since the Bragg reflection wavelength of an FBG changes as the temperature of an FBG changes, it is known that the sensitivity of the sensor is dependent on temperature of the FBG and may vary considerably when the environmental temperature varies. Except for the operation under the situation in which the temperature change is small, therefore, it is generally required to stabilize the sensor against the temperature change in the environment. In this paper we propose a new method to stabilize the sensitivity of an FBG vibration sensor in the temperaturevarying environment by automatically shifting the wavelength of the source laser. The sensitivity variation of the thermally stabilized sensor is reduced down to 3 dB, which is more than 55 dB without the stabilization.

A phase-locked optical-fiber fluorescence temperature sensor based on double-reference light sources is proposed, which results in a significant improvement in the measurement resolution. The system uses the methods of phase-locked, frequency modulation and phase modulation. The double-reference light sources is used to solve the leakage of intrinsic exciting light which has influence on fluorescence decay signal. Ruby of fluorescent substance is used as sensor material in the system. The probe is tested in the temperature range from 0°C to 200°C. The experimental result shows that the system of measurement temperature is feasible and also proposed to be used for the highly accurate monitoring of the real time.

In this paper, we report novel long-period fiber gratings (LPFGs) fabricated by using a new writing method, which is mainly based on the thermal shock effect of focused high-frequency CO2 laser pulses at several kHz. A number of unique characteristics of such a LPFG, such as bend, torsion and transverse-load, et al, are observed by experiment, for the first time, to our knowledge. Based on these unique characteristics, a novel bend-insensitive LPFG sensor that could solve the problem of cross-sensitivity between bend and other measurands, a novel torsion sensor that can realize absolute measurement of twist rate and a load sensor that can achieve simultaneous measurement of transverse load and temperature using a single LPFG element are demonstrated. These unique features are mainly due to the asymmetrical distribution of the refractive index on the cross-section of the LPFG induced by highfrequency CO2 laser pulses.

We have developed the all optical high-precision water level sensors based on fiber Bragg grating (FBG) technique, which are applied for actual fields such as rivers, lakes, sewage systems and so on. The sensor head consists of a diaphragm, a customized Bourdon tube and two FBGs, one for tensile measurement and other for temperature compensation. The FBG attached to the Bourdon tube is strained as the water level increases, and causes center wavelength shift of the reflected light fromt he FBG, which is detected by the wavelength interrogation equipment composed of a tunable Fabry-Perot filer. We have achieved the sensor accuracy of +/- 0.1% F.S., i.e. +/- 1 cm in case of full measurement range of 10 m. Several sensor heads can be connected in series through one optical fiber and each water level at different places can be measured simultaneously by one wavelength interrogation equipment.

Fiber Bragg grating (FBG) sensor systems have been widely developed and the feasibility of their application to various fields has been demonstrated. However, from the viewpoint of the combination of highly multiplexed system and hybrid sensing of static parameter and dynamic parameter, investigations are not adequate yet. In this paper an interrogation technique for static and dynamic FBG sensors is developed. We demonstrated that the method could measure the temperature within 1°C and detect a frequency signal up to 300Hz. We designed a multiplexing method and evaluated that the multiplexed FBG sensor system was able to monitor a maximum of 192 FBG sensors. As a result, we confirmed the applicability of the system for large-scale monitoring of temperature, strain and vibration.

In this paper, a single long-period fiber grating (LPFG) element written by focused high-frequency CO2 laser pulses is demonstrated for simultaneous measurement of transverse load and temperature, for the first time, to our knowledge. Temperature and transverse load can be directly measured by detecting the resonant wavelength shift and the resonant peak amplitude change of the LPFG respectively, as there are two special circular orientations along the fiber axis where the resonant peak amplitude change of the LPFG has a linear relationship with the load applied and is insensitive to the resonant wavelength shift. Such a sensor could solve the cross-sensitivity problem between transverse load and temperature due to the unique feature of this type of LPFG, i.e. the wavelength-load-sensitivity of the LPFG strongly depends on loading orientations due to the non-uniform distribution of the refractive index on the cross-section of the LPFG caused by the thermal shock effect and other effects of the high-frequency CO2 laser pulses exposure method used.

A novel bend-insensitive LPFG sensor written by high-frequency CO2 laser pulses is demonstrated, for the first time, to our knowledge. Experiment results shows that the bend-sensitivity of the novel LPFG depends strongly on curved orientation. The resonant wavelength shifted merely —0. 01 8 nm even for a curvature of 1 . 1m-1at the most bend-insensitive position. Such a bend-insensitive sensor could be used to solve the problem of cross-sensitivity between bend and other measurands, such as temperature, strain or refractive index, which is an unsolved problem for LPFG sensors in practice. In addition, the bend sensitivity of the LPFG can be adjusted by selecting its circular positions.

The paper reports a novel optical fiber fluid flow sensor which is based on the measurement of magnetic-field-induced displacement. This sensor can be used to achieve volumetric flow and mass flow as well. The mechanical part of the sensor is similar as that of conventional turbine flowmeter, except that the single turbine is replaced by a dual-turbine structure. The two turbines are connected with a spring, and their relative position is specially designed that, the rotation phase delay between the two turbines is proportional to the mass flow through the conduit. Two magnets are embedded in the two turbines respectively, and two magnetic field probes are used to measure the rotation phase of turbine by detecting the position of each magnet. The signals from the probes are transformed into light pulses by optical fiber shutter sensors and then transmitted to the central controlling room. A post processing unit receives the light signals, and then calculates out volumetric flow and mass flow value. Compared with other kinds of mass flowmeter, this sensor is rather cheap and inherently safe. Experimental results show that the error of less than I % could he achieved with this sensor.

The monitoring of the fluorescence lifetime of selected materials has been one of the more successful schemes in optical fiber temperature sensing. In principle, both the rise of the fluorescent signal at constant excitation and its decay are described by a first-order exponential, where the time constant ? is a function of the temperature. However few corrections must be introduced to account for instrumental contributions resulting in a baseline offset B, noise and radiation leakage from the excitation source into the detection channel. These corrections can be better applied by means of a digital signal processing circuit. The system uses modified digital phase sensitive detection with phase locked to a fixed value and the modulation period tracking the measured lifetime. It can compensate for correlated and uncorrelated offsets of the decay signal and to work with very low signal-to-noise ratio. The test results give a typical resolution of 0. 1 % for decay. Such a system has been applied to measuring the fluorescence decay time of a chromium-doped YAG crystal used as s sensing element of a optical fiber thermometer The calibration of the thermometer has shown a temperature resolution of 0. 1 0C from OC to 100 0C.

The research of the optical level gauge is to realize its use in oil tank. Its fundamental structure and principle of operation are introduced, especially the technique of double light paths is adopted in order to avoid the influence caused by temperature and the bending resulted from installing and own weight. The experimental set-up and measured data of 40m alignment experiment, the basic experiment using cube corner retroreflector(CCR) and experiment using single wavelength coupler are respectively presented. Some adjustment problems of optical path are analyzed and resolved. It is proved that the selections of single-mode and multimode fibers are suitable through experiments. The right method of optical design is given through experiments and analysis, which effectively reduces the demand for linearity of CCR in moving, that is, to extend the effective diameter of receiving light spot as possible. Finally, the further improvement of optical design-using polarized light and further reducing diameter of CCR are presented in order to easily mount the device on the tank on the basis of the above researches.

Based on the characteristic of thermal induced nonreciprocity in coil of fiber optic gyroscope (FOG) and the heat-conduction model, a simple and universal model was worked out. It is a low-pass and time delay response to temperature. The model was digitized with a digital smooth filter process and a time delay process and the experimental study was done with an open-loop FOG. The bias drift due to temperature was reduced to 18.2% of that before compensation.

The characteristic of Erbium-doped superfluorescent fiber source was introduced. The double pass backward configuration superfluorescent fiber source was demonstrated mainly and two wavelength selected reflector, thin file filter and fiber bragg grating, were taken to form two superfluorescent fiber source. Their whole parameters, including power, spectrum and spectrum width, were tested, the coherence was calculated and the mean wavelength temperature stability is tested too. The result proved the superfluorescent fiber source with thin film filter and fiber bragg grating are both suitable to inertial grade fiber optic gyroscope.

Fiber Optic Gyro (FOG) is the most typical application example of fiber optic rate sensor. Theoretically, as the potential inertial sensor of next generation, FOG shows considerable advantages over mechanical gyro in many aspects, such as all-solid-state configuration, no-spinning part and etc. Its promising features bring the following performance: vibration-proof and interference-proof and high reliability. As to the practical application, shock and vibration should be considered when the potential drift sources are concerned. The stress change of fiber coil, the vibration of the optical device pigtail and structural resonance would increase dynamic error. Recently, the engineers on development of FOG and its strapdown system focus on how to eliminate or decrease the vibration error of FOG and make good advantage of this kind of gyro.

Based oii quantum theory and combined with the nonlinear effects of both Stimulated Raman Scattering (SRS) and Simulated FoLirth-photon Mixing (SFPM), the correlation among the pump, the input signal and the output in the Raman amplified fiber-optic transmission systems, is calculated and analyzed. Synthesize the correlation function group and program the corresponding software package. And when the ratio of the pump to the Stocks waves is in a certain field, the correlation is comparatively high, the corresponding input signal amplification multiple ? gets to the extreme field. And when the ratio of the pump to the Stocks waves is oversize or undersize, the correlation is decreasing correspondingly. The conclusion of this letter is benefit to optimize the design and experimental research of Fiber Raman Amplifier (FRA).

Digital speckle correlation method (DSCM) is one of the most important tools for deformation measurement and fluid inspection. Definitions of the correlation coefficient, search schemes and sub-pixel estimation methods are three key problems to the development of DSCM. In this paper, various improvements in literatures concerned on these three key problems are compared and some new techniques are developed according to the comparison. An experiment using SEM images is completed to reveal the ability of micro-deformation of DSCM.

A new scanning mechanism for a long optical path change in an interferometer is proposed. It consists of corner reflectors, arranged on a rotating disk at regular intervals, and an outer mirror. A reference beam in the interferometer is reflected on the corner reflector and the mirror, and then comes back to the same way whenever the reflector moves along to the disk rotation. This action makes it possible to obtain a long path change with nearly linear motion. An optical path length change, a scanning speed, and a repetition rate can be designed suitably. The rotating disk of the diameter 120mm gives the optical path change of more than 40mm. The deviation of the optical path change against the linear motion is less than 0.3%. An optical coherence tomography system with the proposed long path optical scanner has been developed and evaluated the motion characteristics. With the disk size mentioned above, the maximum repetition rate was designed as 15scans/s at the disk rotation of 60rpm. We have demonstrated the fundamental experiment of samples such as stacked slide glasses and a mirror separated from a slide glass. The experiment was in good agreement with the prediction.

In this paper we present a new filtering scheme for processing of DSPI fringes and implemented the same to measure the out-of-plane vibration in a rectangular plate fixed at one end and free at another end. Values of the amplitude measured by DSPI and accelerometer are in good agreement. Also mode shapes obtained from the experimental data and from the theory are almost similar.

Power management is an increasingly concerned issue in all-optical network, where the continuous adjustment of the transmitted power is required. In this paper, the diffractive optical propagation inside a magnetic actuated, surface micromachined variable optical attenuator has been modeled and characterized. The modeling of the diffractive optical propagation is based on a gaussian beam approximation to the fiber mode, a calculation of the free space diffraction past a square aperture based on the Fresnel-Kirkhoff diffraction integral, and the mode-overlap integral between the diffracted beam and the fiber mode. The fabrication of the attenuator is based on the nonsilicon surface micromachine technology. The experimental data is in good agreement with the theoretical calculation result. Based on the work, a variable optical attenuator (VOA) has been successfully developed.

A digital processing method for quasi-white light interference signal is proposed in the paper. A circuit based on EPP (Enhanced Parallel Port) is designed for high speed synchronous collecting. Envelope signals collecting is realized by means of interference fringe pulses synchronization, with the result that the space-domain interference envelope signals can be restored with high accuracy. A high accuracy algorithm for finding the acme of interference envelope signals, namely the point of zero optical path difference, is proposed in the paper. Compared with the traditional processing method based on analog circuit, the new method overcomes the time-domain wave distortion of quasi-white light signal caused by the uneven moving velocity, therefore, the errors caused by the distortion are eliminated. The method is applied in the interference signal processing of long coherent length. In the paper, the proposed method is emulated with computer and proved by experiments, and the results indicate that the locating accuracy of the points of zero optical path difference of fiber quasi-white interference signal is better than 0.5 interference fringes.

In smart structures applications where fiber sensors are embedded within structural materials, multiple lead in/out fibers are preferred for redundancy and improving reliability. The use of only one lead/out fiber is not optimal because the breakage of fiber at one location due to for example local structural damage would cause the failure of the whole sensing system. The multiplexing and networking techniques suitable for such applications have attracted considerable research recently. In this paper, we summaries the results of our recent investigation on the bi-directional interrogation techniques (BDIT) for white light interferometric sensor arrays.

A single-component dual-optic paths acceleration seismic geophone based on all-fiber Michelson interferometer is developed, which can detect the acceleration less than 0.01g. In order to obtain the elastic modulus changing of compliant cylinder after rolling fiber, the key component of the sensitive unit, a compressing test and a stretching test are carried out. And at the end of the paper a three-component acceleration seismic geophone based on the single-component one is discussed.

ZnSe and InGaN based white-LEDs have been utilized for an interferometer. These white-LED consist of blue-LED light and yellowish green one. When these white-LED were modulated by rectangular wave, there were differences in response speed between blue-LED light and yellowish light. The response speed of blue-LED light of ZnSe type white-LED was 50ns, while that of yellowish light was 5?s. The spectral bandwidths of the blue-LED light and the yellowish light were 10nm and 100nm, respectively. Coherence lengths of these lights were 10?m and 2?m, respectively. Combining the blue-LED light with the yellowish light, we observe an unique interference when scanning the optical path of the low coherence interferometer. We also propose a method for a color separation of an interference in a low coherence interferometer with the ZnSe white-LED modulation. The ZnSe white-LED was modulated with much higher frequency (100kHz) than the Doppler frequency of the above interference. The interference fringe of white light appeared at the upper side on the rectangular modulated light emission, while that of the residual yellowish light was presented at the bottom. The interference fringe of the blue light was derived by subtracting the yellowish light interference from the white light one.

The principle of all fiber Mach-Zehnder interferometer as an optical filter was investigated in this paper. All fiber Mach-Zehnder interferometers with single-pass and double-pass configuration were manufactured and used in the measurement of spontaneous Brillouin scattering. The separation of backscattered spontaneous Brillouin from Rayleigh with low losses was achieved effectively. With the Mach-Zehnder interferometer, a direct optical detection method was used in Brillouin OTDR, by which a new detection method for distributed sensing system based on spontaneous Brillouin scattering was proposed.

In the paper, a set for measuring terrain atmospheric visibility is put forward. Principle of the set operating is discussed. The processing of the signals in the set is analyzed. Optical fiber beams are utilized. The fiber beams act as both a field stop and a spatial filter. The errors caused by the limit of the end faces of fiber are smaller than 3.0 % in the set.The errors can be eliminated by means of adjusting the instrument constant of the set. The effect by the forward scattered light on the measuring of transmission light is cut down due to the spatial filter. The measuring of angular scattering coefficient is not affected by the change in the intensity of probing beam, and change in the properties ofpropagation by the depositing of dust. The set can be used in the real-time measuring of visibility. The relative error is about 3.7 % between the total scattering coefficient and that by the transmission light method.

A long-period grating (LPG) fiber optic sensor has been developed for monitoring the relative humidity levels and toxic chemicals, especially the chemical warfare agents. The principle of operation of this sensor is based on monitoring the refractive index changes exhibited by the reactive coating applied to the surface of the LPG region in response to analytes. Specific interaction of the analyte with the thin film polymer coating produces as the output a wavelength shift that can be correlated with the concentration of the analyte. Thin polymer coating for relative humidity sensor is made of carboxymethylcellulose (CMC) covalently bound to the surface of the fiber. Coating for chemical warfare agent detection employs metal nanoclusters imbedded in polyethylenimine (PEI) for specific reaction. The relative humidity level can be determined from 0% to 95% and the level of toxic chemicals can be determined is at least on the scale of 1 ppm. This small-size and low-cost LPG fiber optic sensor exhibited high sensitivity, rapid response, repeatability and durability. The goal of developing relative humidity sensor is to produce a fiber optic sensor-based health monitoring system for building, while the chemical sensor has found its application in point detection network for chemical warfare agent monitoring.

A new fiber optic glucose biosensor based on oxygen fluorescence quenching using lock-in technology has been presented. Ruthenium(II) complex, Ru(bpy)3Cl2, were used as the fluorescence indicator and cellulose acetate(CA) were used as the matrix membrane to immobilize the indicator and GOD, and the optimal conditions for the preparation of CA membrane has been studied. For the immobilization of GOD to CA membrane, albumin of bovine serum(BSA) and glutaraldehyde(GA) were used through covalence—cross bonding process. The relationship between the concentration of glucose and the phase delay??? has been studied, the results show that ??? has good relationship within the range of 50mg/dl—500mg/dl and the response time is less than 30 sec. Several factors to influence the sensor such as pH of the medium, the additional membrane layers, the properties of CA membrane have also been studied. The results indicate that its best pH range is between pH6.0 and 7.0, and the thickness of the additional membrane layers on the sensor head will influence the response time greatly, that is, the response time is controlled by the speed of dispersion of the dissolved oxygen into the fluorescence dye layer.

The sensitivity of output power of erbium fiber laser to intra-cavity loss is investigated theoretically and experimentally. The laser rate equations are modified to analyze the output characteristics of fiber laser under different pump powers and intra-cavity losses. The high sensitivity can be achieved when pump power is close to threshold value. Experiments are carried out and the results agree with the theoretical expectations. An intra-cavity gas sensor is demonstrated experimentally.

Permanently microbent fibers are potential candidates for chemical sensing 1. They behave more or less like an unclad optical fiber in many respects and the basic mechanism involved in chemical sensing application is the evanescent wave absorption. In this manuscript we propose its usage for refractive index measurement of solutions. The sensing configuration employed here is the dark field detection configuration which essentially involves the detection of cladding modes generated in and near the microbent region.

Delayed light emission (DLE), which mostly produced from chioroplast, can be an indicator of plant living ability. We have proved that environment stress can reduce the intensity of DLE. Our prior experimental results showed that there exists a linear relationship between DLE intensity and chloroplast concentration in a certain concentration range. Plant chloroplast's energy is sensitive to environmental stress. Considering the close relationship between DLE and environment stress we directly detected environment pollution by measuring DLE with a sensitive imaging system, which consists of a tungsten lamp excitation source, an ICCD digital camera, a controller and computer. Instrumental parameters (optical excitation time, optical source power, and exposure time) were adjusted independently to optimize measurements. Computer through controller collected all data. All images were analyzed with WINVIEW software. This experiments conducted with plant leaves treated with model acid rain (vitriol, pH 5.0) and exposed to moderately elevated troposphere sulfur dioxide environment demonstrated the environment stress could be inspected sensitively by measuring plant DLE. Our experimental results showed that when acid rain less than five zero could be inspected sensitively. It was also indicated that moderately elevated sulfur dioxide cause direct damage to the plant by reducing photosynthetic activity through partial stomata closure and other mechanics.

Chlorine (C12) gas sensors were newly developed using metal-phthalocyanines (MPc) such as CuPc, MgPc, ZnPc and FePc. All gas sensors using MPc thin films deposited by a vacuum evaporation method exhibited an increase in conductance with exposure to C12 gas at an operating temperature in the rage from 25 to approximately 200°C. The obtainable sensitivity of sensors was considerably affected by the MPc material used and the deposition conditions. The transient response of sensitivity was strongly dependent on the operating temperature of the MPc thin-film sensors. The increase in conductivity of the MPc thin films used in sensors that results from an increase in C12 gas concentration can be explained by the increase of carrier concentration dominating the effect of a decrease in Hall mobility. A high sensitivity as well as a fast response were realized for CuPc and MgPc thin-film sensors operated at approximately 200°C; C12 gas at a concentration of 0.18 ppm could be detected using these thin-film sensors operated in the range from 25 to 200°C.

A cost-effective multiplexing fiber-optic remote monitoring system, which laboratory prototype, has been demonstrated. This monitoring system will help personnel to measure a spatial distribution of methane or other gases in a wide area. And the fundamentals of the remote detection are based on Frequency-Modulation Spectroscopy (FMS) technique and harmonic detection technique. By utilizing fiber-optic splitter, a component of telecommunications industry, the remote monitoring system is feasible employing single laser source to get multicenter measurement in the near infrared region. The system described here performs sufficient sensibility, considerably increased reliability and marketability over the presently available system. It results in a large potential for applying extensively to various strategic points within the environment, such as solid-waste landfill sites and mines as well as urban and residential areas and otherwise.

novel handy oil tank liquid level measuring system with optically powered is presented. To realize handy and simple structure, optical powered and micro- consumption detection, the system has taken the PWMIPPM modulation, time division multiplexing (ThM), ratio measurement and pulse width division multiplexing techniques. So, the multiple parameters measurement driven by optical power and transmitted by single optical fiber is also realized. This new transducer has provided with high characteristics: experimental transmitting distance is 500m; total power consumption of the probes is less than 150uw; measurement error: ±0.10( in the measured temperature range of —20-50C) and ±0.04KPa(in the measured pressure range of 0-100Kpa). The measurement accuracy of the liquid level and reserves is mainly determined by the pressure accuracy.

In this paper, a portable fluorescence optical-fiber measurement system for identification of oil species is presented, which is based on fluorescence spectrum analysis, and combines the optical-fiber sensing technique and computer data processing technique. Fluorescence spectroscopy is enjoying increasing popularity as a technique for qualitative and quantitative analysis. Because of its great sensitivity, it is becoming an important tool for the identification of the type pf oil especially at low concentration levels. Conventional fluorescence methods suffer from low selectivity and are generally ineffective in spectral structural elucidation of carious oils because the different oil has fluorescence spectrum overlapping to great extent. The three-dimensional fluorescence spectroscopy overcomes the above-mentioned shortcomings. In this paper, the principle of 3-D fluorescence spectrum parameterization is introduced as a new spectral analysis method. The main feature parameters are mean, standard deviation, origin moment, marginal distribution, center moment, correlation coefficient and compression ellipse. We obtain the 3-D fluorescence spectrum of four kinds oils (crude oil, diesel fuel, kerosene, machine oil) by using fluorescence spectrophotometer in the lab and extract the feature parameters, which are weighting processed according to their sensitivity to the oil species for identification. The result suggests the degree of accuracy is as high as 95%.

The distributed optical fiber Raman Photons Temperature Sensors (DFRS) is a real time, on line and multi-point (30k points) measuring system for multi-parameter measurement of temperature etc. According to temperature effect of optical fiber Raman backscattering, the intensity of anti-stokes Raman backscattering of optical fiber is modulated by the spatial temperature field where the optical fiber is laid. Then after signal processing and demodulation, the information of temperature can be extracted from the noise and can be displayed in real time. It is a typical optical fiber sensors measuring network. In time domain, using the velocity of light wave in optical fiber, the time interval of back-direction light wave and optical fiber OTDR technology, the DFRS can locate the temperature spots. In this case, it is a typical optical fiber laser temperature radar system as well. The backscattering spectrum of optical fiber has been measured by fiber laser and optical spectrum analyzer. Raman backscattering spectrum and ZX band backscattering spectrum has been first observed. The amplification of anti-stokes Raman spontaneous scattering (ARS) and the temperature effect have been first observed and applied to DFRS. The performance of DOFS is following: fiber length : 25.2km;temperature measuring range: 0-1000C(can be expand) temperature uncertainty: ±200C : temperature resolution: 0. 1; spatial resolution: 5m: measurement time: 10mm; Main unit operation temperature range: 0—400C . The optical fiber sensor probes and the software for signal processing are also discussed.

Brillouin optical time domain reflectometer (BOTDR) using microwave heterodyne detection is able to measure the longitudinal strain distribution along an optical fiber with high accuracy and high stability, and is thus regarded as an effective tool for structural monitoring. However, the frequency shift of Brillouin scattered light varies in proportion to the fiber's temperature as well as to the strain applied to it, and thus the measured Brillouin frequency shift simultaneously includes strain and temperature information. By combining BOTDR with OTDR, we propose a method whereby it is possible to make precise separate measurements of the temperature distribution and strain distribution along an optical fiber. This method involves making simultaneous measurements of an optical fiber's Brillouin scattering distribution and Rayleigh scattering distribution (loss distribution). The net change in the Brillouin scattering light power is then determined using the Rayleigh scattered light, which does not depend on temperature or strain. In this way, it is possible to accurately separate the temperature and strain effects by solving a simultaneous equation related to Brillouin frequency shift and Brillouin scattering light power. Since the measurement ofthe loss distribution by OTDR is affected little by polarization noise and fading noise, the net fluctuation ofthe Brillouin scattered light power can be determined with greater accuracy. We have used this method to measure temperature and strain distributions with a spatial resolution of 1 m. The strain measurements have an accuracy of±50 ??, and the temperature measurements have an accuracy of ±50C

In this paper, a novel technique for multiplexed fiber Bragg grating (FBG) sensors is proposed. Applying the synthesis of optical coherence function, we can select the signal, which has a specific time delay with the reference light wave, and therefore FBG array with the same reflection wavelength can be used.

In the development of distributed optical fiber temperature sensors, there is big noise in the measured temperature curve. The noise is caused by the fluctuation of laser power. If the laser power fluctuates more than 5%, then there will be very large noise in the demodulated temperature OTDR curve. A new method called dynamic base line matching is taken to eliminate this noise. The experiment result is quite well

This paper describes a novel correlation-based technique for fiber optic distributed strain sensors using Brillouin scattering. Conventional Brillouin-based sensors utilize a pulsed-pump similar to that of OTDR and are capable of distributed strain sensing over large distances, but suffer an inherent spatial resolution limit of around 1m. In addition, unlike FBG-based strain sensors which are competent of measuring dynamic strain, the pulse-based Brillouin sensors have large measurement times of several minutes, making them inadequate for dynamic strain measurements. On the other hand, using the correlation-based continuous-wave technique, we have achieved static distributed strain measurements of up to 1cm spatial resolution, and dynamic strain measurements of up to 8.8Hz from a 5cm strained section.

A Brillouin scattering based fiber sensor system has been developed by our Fiber Optics Group for the structural monitoring and civil engineering related applications. In this paper, the Brillouin loss spectrum has been characterized in terms of its center frequency, peak power, line-width and shape. These parameters have been considered as a function of the input pump and probe laser powers, the pump pulse duration, strain and temperature. The measurement accuracy has been studied at different Brillouin frequency steps to study the uncertainty of the Brillouin frequency, line-width, peak power and shape factor vs. signal to noise ratio, so that we can optimize the system performance. Characterization of the Brillouin loss spectrum led to the development of an innovative technique to measure the strain and temperature simultaneously using the strain and temperature dependence on the peak power in conjunction with the Brillouin frequency for the single mode fiber with 3m spatial resolution, 3°C temperature resolution and 200 ?? (?m/m) strain accuracy.

We present a simple method for the localization of a loss region for a fiber-optic alarm-condition sensor based on the measurement of transmitted and Rayleigh backscattered power. Bending the sensing fiber affects both the transmitted and backscattered power of unmodulated continuous-wave light that is launched into the fiber. The position of the loss region is determined from unique relationships between normalized transmitted and backscattered powers for different locations of the disturbance along the test fiber. The localization of a strong disturbance with an estimated accuracy of few meters along a few km-length single-mode test fiber was demonstrated.

Temperature dependence of spontaneous Brillouin intensity in a dispersion-shifted fiber has been investigated in a wide temperature range theoretically and experimentally. It has been found that Brillouin intensity varied with temperature linearly in the range —27 °C to 819 °C by a coefficient of(0.26±0.02)%/°C after the fiber coating was pyrolyzed totally. Temperature measurement in the range above has been realized with a spatial resolution of 13 m at the end of 4 km long test fiber, which demonstrates the feasibility of the present system for the distributed sensing of wide-range temperature.

A distributed temperature sensing system based on optical fiber Brillouin scattering is presented in this paper. A distributed temperature sensing measurement was achieved with a BOTDR system. The light source was a narrow linewidth LD. The light from the LD was modulated by an AOM and amplified by a high gain EDFA to generate high power light pulses. So a high intensity spontaneous Brillouin scattering can be achieved. A double-pass all-fiber Mach-Zehnder interferometer was designed and used to separate Brillouin scattering from Rayleigh scattering.

A wide variety of techniques for manipulating 3D objects in VR (Virtual Reality) systems have been implemented recently. But the shortcomings of the present interaction devices limit the types of manipulation that the user can perform in the virtual world. In this paper an interaction device that enables the user to interact with the virtual environment with different gestures is presented. By measuring the joint angles of the individual fingers with fiber optic sensors and tracking the relative position and orientation of the palm with AC (Alternating Current) pulsed magnetic tracker, the proposed interaction device can track an enormous variety of gestures and give the VR system remarkably rich expressive power. The relationship between the output of the fiber optic sensor and the actual flexure angle is studied. A digital phase sensitive detector is constructed and an iteration algorithm is used to extract the amplitudes of the received signals of the magnetoresistive sensors. The algorithm to calculate the spherical coordinates from the output of the accelerometers and magnetoresistive sensors is deducted. The design of the proposed interaction device and the experiment result are also presented.

Nippon Telegraph and Telephone Corporation (NTT) has developed a device (BOTDR) for measuring the strain occurring in optical fibers as a means of monitoring the condition of optical fiber telecommunications cables. The authors are promoting development of a system that uses this device to measure and monitor structural and ground deformation. This paper first introduces the measurement principle of the strain measurement method using optical fibers (BOTDR method). It then presents case studies of application to the deformation of telecommunications tunnels, ground subject to landslides and so on, and also an outline of an automatic measuring system.

This paper describes a novel fiber-optic level sensor designed to measure the level of benzene, diesel oil and other chemical liquid discretely or continuously. It is an intensity-modulated on-off switching sensor whose operating principle is based on the frustrated-total-internal-reflection effect caused by the refraction index change of the surrounding medium. The sensor head is made from standard multi-mode communication silica fiber with a taper tip. Different tip shapes and fabrication methods were studied and the maximum signal contrast of 15 dB of the sensor tip has been obtained. The experiment results demonstrated that the resolution of the system of 10?m and the level measurement accuracy of ±0.5 mm have been achieved in a continuous measurement range of 2m.

This paper introduces a non-contact measuring system —measuring thread system using laser fiber sensor. It can solve some problems of the traditional measuring methods, such as complicated technical process, long re-testing periods, waste workpiece. A low noise amplifier used to match the photo-electronic detecting element due to the weak signal is applied in this system. Furthermore, it presents a new measuring system with phase-sensitive detecting circuit controlled by computer program, an interface circuit of microcomputer, laser fiber sensor system and digital processing system, the system based on the above elements has high resolution and sensitivity, the measuring errors ?20 ?m.

Fiber Bragg gratings (FBGs) have attracted a lot of attention in recent years due to their wide applications in optical telecommunications and smart sensing. They have been used as DWDM filters, dispersion compensators, gain flattening filters, optical switch and connection devices, and temperature/strain sensors. FBGs have been found to exhibit four different type structures according to their different growth mechanisms. Each type of FBG exhibits unique thermal and strain properties. Generally, the Type I gratings in hydrogenated and hydrogen-free fibers are used most for applications. However, some novel devices may be achieved by combinational structure of different types of gratings in the future. In this paper, we propose a novel concept of fabrication and application of FBGs with hybrid grating types. We have observed a complex growth behavior of a hybrid-type grating in the UV exposure to a B/Ge codoped fiber through a phase mask. A new model has been developed to simulate the complex growth behavior of the hybrid-type gratings, giving results in excellent agreement with experiment.

This paper presents a review of the sensor research at Virginia Tech Center for Photonics Technology. Some of these sensors are intended for energy-production and energy-intensive industries, such as power, oil, coal, transportation, metal casting, and glass manufacturing. The sensors of different types are presented. Some recent experimental results are briefly discussed.

Potential low-cost strain, vibration and temperature sensor systems based on draw-tower fabricated fiber Bragg grating arrays and spectral high-resolution polychromator interrogation have been developed. Performance has been demonstrated in field tests of electric power generators, aircrafts and spacecraft structures, railway tracks, and in rock-bolts for mining and geotechnical engineering.

Extinction ratio is an important parameter of a polarizer, and the bias angle of the polarizer used in optical current sensing systems is also an important adjustable parameter. Both them can certainly affect the performance of the sensing systems. In this paper, the effects of the extinction ratio and bias angle error of polarizers upon the output characteristics of an optical current sensor are investigated theoretically and experimentally, some useful results are given for the optical current sensor designers.

In a Faraday optical-fiber current sensor, it has many kinds of linear double refraction inevitably because of the circular degree error of the optical fiber, deformation of pressure, temperature effect and other reasons. It results in an additional phase difference, which will affect the detecting sensitivity and even decrease it to zero. A new method that can eliminate the effect of linear double refraction is offered in this paper with phase conjugate device after analyzing the foundational operation principle of the Faraday optical-fiber current sensor and the effect of the linear double refraction.

The report describes a 110kV active optical fiber current transducer (AOCT). The transducer is different from the passive one, because a special power supply is designed for high-voltage unit and none optical crystal or magneto-optical fiber is used. The AOCT consist of three parts: a high-voltage measurement unit, a low-voltage signal processing unit and an optical fiber link which connects theses two units. As a result, the safe protection is reliable for the low-voltage equipment and the operation staff. Compared to the conventional current transformer, the advantages of the AOCT are high accuracy, low cast, small size, wide bandwidth, excellent dynamic characteristics and immunity from electromagnetic interference. The 110kV AOCT has been tested and its accuracy could achieve ±0.2%.

In the testing and control of electricity system, Magnetism-photo optical fiber electricity sensor modules based on Faraday Effect of the main electricity wire can be made. We can play these sensor modules at the spots where the electricity need to be tested and controlled real-timely and make use of the Wavelength Division Multiplexing (WDM) technique of optical fiber network to transmit the real time data from all spots to the central computer, so the system of distributed optical fiber electricity current supervision and control is constructed.

An optical electric-power sensor is proposed and experimentally carried out. Only one block of bismuth germanate crystal is utilized as the sensing element, which exhibits both the Faraday effect and the Pockels effect. The polarized light passing through the crystal can be modulated by the product signal of applied electric and magnetic fields, therefore, instantaneous electric power signal can be obtained when load current and load voltage are simultaneously applied to the sensing crystal by use of an air-cored coil and two plane electrodes. The active power and apparent power within 2000W(or VA) have been measured simultaneously under different power factors. The maximum relative errors are 2.7% for active power measurement and 1 .9% for apparent power measurement. The sensitivity and uncertainty ofthe sensing system are also discussed.

Based on the fiber-optic measurement technology, an experimental prototype is established for the inspection of dynamic gap between the gas turbine stator and blade. The structure of fiber optic sensor and encoding technology are proposed. A novel probe and the circuit with APC and soft startup are designed. The experimental results show that the fiber-optic sensor system could implement the vane dynamic gap measurement in the formidable on-site operation conditions with high temperature and rotating speed. Because of the superiorities of this kind of sensor such as simple structure, convenient to use, and the high measurement accuracy, there is an attractive application foreground on the turbine and other complex measurement problems.

This paper discusses the working principle of reflective fiber optic sensor with intensity compensation for simultaneous measurement of displacement and surface roughness. The sensor with a single sensing head is a combination of an illuminating fiber bundle transmitting incoming light beam and two receiving fiber bundles employed to collect the reflected beam from the workpiece surface. Three fiber bundles with same type are put together and arranged side by side, but the two receiving fiber bundles endface have different distances from the workpiece surface. The output characteristics of the sensor are analyzed. Although the sensor can simultaneously output two different readings containing displacement and surface roughness information using such a sensing head, it suffers from the influence of the cross-sensitivity and non-linearity. An intelligent signal processing method based on artificial neural network for the sensor output is proposed. The artificial neural network is trained to properly represent the complex nonlinear mapping between the sensor outputs information and the actual sensed measuring values. The example shows that the method can be used for both separation and linearization of the sensor output signals. Wide measuring range and high measuring precision of the two parameters are also obtained by means of the artificial neural network.

Turbine blade is high-reflective metal surface, which has much difficulty in measurement. Based on vision measurement technique and the metal superficial polarization characteristic, the probe system with three cameras is developed. On the basis of geometry model, the impacts of structure parameters on vertical resolution ratio of the system are analyzed and the parameters are designed, which offer the theoretical foundation of sculptured high accuracy surface measurement online. In measurement, the CCD calibration is very important. Combining with Tsai algorithm, the camera model is built, the uncertainty image scale factor sx scan be got, and the other parameters can be received easily. With the method of the paper, the experiment of high-reflective surface measurement of gauge block is carried on. The results indicate that the measuring device has high measurement accuracy, which can be widely used in practice.

Based on vision inspection technique, the measurement system for measuring complexity free form surface is developed. For getting the high-accuracy object surface, subpixel subdivision technology is studied. For the sake of the data got from the measurement are scatted measuring points, modeling technique for triangular meshes should be used. The basic idea of the approach based on Bezier interpolation can be expressed. A practical algorithm for free form surface reconstruction combining Bezier triangulation modeling and NURBS rectangular modeling is proposed. In 3-D digital image modeling the merging of depth images is one of the key techniques, which directly affects the quality of depth image merging. The multi-view image data processing is introduced. Serve the turbine blade as the object, with coordinate measuring machine, the demonstrations of the designed measuring system and the image processing method are proved. The results indicate that the studied method of the paper is high accuracy, speediness practicality characteristics for measuring the complexity free form surface.

A novel of bend sensor is demonstrated firstly. The device uses a simple support beam composing of two beams with a metal line winded on each beam and multimode fiber of a few meters in length which is placed between two beams having metal teeth profile such that the fiber experiences multiple bends. The experiment shows that the microbend loss of the multimode optical fiber is sensitive to the simple support beam bend curvature. The microbend loss with curvatures from 0 to 4.4m-1 is examined. The microbend loss with curvature is nonlinear, with a minimum detectable curvature change of 0.0175m-1.

Using the microbend characteristic of the multimode optical fiber, a novel twisted fiber strain gauge is demonstrated. The experimental principle is analyzed, and the experiment shows that the microbend loss of the multimode optical fiber is sensitive to the distortion. The sensitivity is 3.5dB /?? . The experiment results agree well with the theory.

The linear fiber sensor of torsional angle with biderectional tuning has been designed and realized by using multi-mode fiber and torsion beam. The optical power loss of the multi-mode fiber is linear to the torsional angle of the torsion beam under the torsional strain is not large. In the range between -40 and +40 , we obtained that the sensitivity of the torsional angle is 0.376dB/degree for positive torsion and —0.374dB/degree for negative torsion, respectively. The experimental results are good agreement with the theoretical analyses.

A new approach for displacement sensing based on chirp effect of fiber Bragg grating under strain-gradient is proposed and demonstrated in this paper. Strain gradient chirp of fiber Bragg grating is realized by attaching the grating slantways on a side face of a simple cantilever beam. The strain gradient, which is formed along the grating when the free of the beam is curved, produces a linear variation in the grating pitch .The theoretical formulae are derived and the experimental results are given. Because bandwidth of the grating is temperature-insensitive, the cross talk between displacement and temperature is avoided. This device has many characteristics, such as simple configuration, good noise immunity, and good linearity (about 0.9992). It is promising to be used into in-process displacement measurement.

A new approach of sensing low frequency vibration is discussed. Fiber optic gyro (FOG) is used as pendulum bob of a simple pendulum in this sensor system to sense angular vibration. The pendulum can be vibrated when the external force in one direction excites the whole system. The angular velocity must be measured firstly. The relationship between angular velocity and accelerated velocity can be given if known natural frequency of the simple pendulum, which can be obtained before measurement. Consequently vibration frequency can be derived. The result shows that this sensor system is sensitive to vibration frequency lower than 2Hz, but insensitive to higher frequency. The breakthrough lies on the different way to measure the vibration frequency. This approach is fit to the measurement of earthquake wave or other construction vibration.

This paper presents the angle detecting principle based on Position Sensitive Detector (PSD). Two approaches are compared, which are plane-reflection and image-reflection. The calculations executed show the former scheme requires lens with longer focal distance, and that the sensor will have bigger size. Because of miniaturization of sensors for ESG theoretical work is mainly done on the latter approach in this paper. After analyzing the angle detecting principle, the mathematical model is derived and steps to calculate displacement of ESG 's momentum are presented. Since the model is a non-linear and implicit function, it is simplified to be easy to realize in engineering application. Based on the simplified model, it is shown that the direct component in the output of PSD is proportional to the polar axis displacement of ESG in a certain range. The result verifies possibility to use PSD as the angle detecting sensor of ESG.

The structure of triaxis fiber optic gyroscopes with frequency division multiplexing and frequency distribution characters of the system were introduced. The relationship among the output signal with modulation frequency and depth was focused on. The simulation results show that the output signal intensity of FOG presents the "hump" effect on condition that the modulation depth varies in a certain range. Then the modulation frequency and the depth of each fiber optic gyro can be optimized. And the cosine-modulated filter banks based on wavelet theory was designed to process the output signal of gyroscopes.

This paper presents a large range, high accuracy measuring method on base of quasi-light fiber interference technology. The system consists of quasi-light fiber locating interferometer and scanning interferometer. The light source of the locating interferometer adopts LD whose light spectrum has been widened by current injection. The locating interferometer has several fiber groups that have different light difference. Furthermore, several fibers are placed in the interference light path to multiply the measuring range two times. Therefore, the system can fulfill large range measurement (more than lOm) only using short guide (200mm). Moreover, the system sets up a zero position fiber group to fix an absolute zero position and fulfills the criterion transfer using light wavelength. The experimental results illustrate that the measuring accuracy is ±2?m and the repetition accuracy is better than 10-5. This paper demonstrates the basic principle of this method, introduces how to achieve the absolute zero position and the multiplication of the measuring range and at last, gives the corresponding experiment data.

We present a new device for determining the state of polarization (SOP) during the measurement of spatial distribution of mode coupling in high birefringent. polarization-maintaining (PM) fibers. The linear polarization light can be randomly rotate to obtain the best experimental result through it. And we draw a conclusion that in the distributed polarization coupling analyzer (DPCA) the fringe contrast is equal to 0.943 when the amplitude ratio is equal to 1. It can be widely used in the PM fiber testing and linearly polarized light interference system.

A direct current sensor based on all-fiber Mach-Zehnder interferometer is demonstrated in this paper. The phases of interferometric lights in the interferometer is modulated by heat effect when current flowing through a thin metal tube. The charactersistics of current sensing are studied experimentally. Adopting the wavelength scale method, in the case of elimination of environmental perturbation, the wavelength changing range is 32nm when the current changes from 0 to 1.8A. The shifting wavelength is linear to the power and the linear fitting is 0.9987. The tuning efficiency is approximately 19.47nm/W.

A new method of fibre-optic sensor for measuring the steam quality is presented in this paper. A sensor based on refractive index modulation is employed. The sensor is made up of a sapphire probe and fiber, the fiber transmits the optical signal and the sapphire probe detects reflectivity of steam. The surface of sapphire probe can be considered as an assemblage of infinitesimal square-meshes, and each mesh can distinguish between water and vapor, because water and vapor has different refractive index. After measuring temperature and reflectivity as well as analyzing the relation between them and steam quality, we can obtain the steam quality. The result obtained in this paper is also important to optimize the system of fibre-optic sensor.

Experimental setup of a reflex dual-differential sensor for salinity measurement is developed. The sensor exploits the beam deviation due to optical refraction at the receiving end face of the measurement cell, which is caused by changes in refractive index with different concentration of salt water. With the help of a right-angle reflecting prism and in the presence of a referenced distilled water cell with an inclined optical window, optical differential measurement of incident beam deviations is implement, and the deviation caused by changes in salinity will be detected by a PSD with an electrical differential signal processing technique. Experimental setup and measurement principle are discussed. Salinity measurement based on this method avoids the influences by intensity fluctuation of the incident light and temperature drift. Preliminary experimental results indicate that the estimated salinity measurement resolution can reach 0.02 ‰ depending on the performance of PSD.

Real-time detecting of the fault gas dissolved in the transformer oil is very important to the safe operation of the transformer. The traditional measuring method, that is chromatogram method, has many shortcomings, such as complicated operating, long analysis period, etc. The article adopted the spectrum absorption method to realize highly sensitive, on-line, remote measuring the main fault gas in the transformer oil, obtained the purpose of watching the transformer's work condition. It was a novel optical fiber sensor. This method offered high selectivity, long life, no influence of surroundings gases, no electric induction and so on. It is adapted to be used in the foul and hazardous environment. Fiber detecting will be realized on the base of separating the gas dissolved in the transformer oil. So the key technology is how to separate the fault gas from the transformer oil. Experiment indicates that polyflon membrane is an excellent medium for the main fault gas (CH4) permeation. A measuring method under unbalanced state based on equal time interval sampling is proposed. It not only decreases the difficulty in designing the gas cell, but also increases the real-time of measurement.

In this paper, a novel method to measure the distributed polarization mode coupling in polarization-maintaining (PM) fibers is introduced. The measurement system is based on white light interference. A super luminescent diode is used as the broadband light source in the system. The whole test system is working on 1300nm wavelength. There are two main parts of the measurement equipment: polarization adjustment and a scanned Michelson interferometer. In order to improve the accuracy, a piezoelectric transducer (PZT) is applied in the scanned Michelson interferometer. The maximum length of tested polarization-maintaining fiber is one kilometer, and the spatial resolution of this method reached 60 mm along the tested PM fiber. The degree of polarization mode coupling that could be detected is —75dB.

Anisotropy in the dielectric constant of a medium having a periodic structure whose period is less than the wavelength of light is known as "form birefringence". Axisymmetric periodic media such as annular layers are expected to have axisymmetric birefringence and mode coupling phenomena in such a waveguide is analyzed theoretically. This paper reports the experimental characterization of the axisymmetric birefringence in an axisymmetric optical fiber. An axisymmetric optical fiber is drawn from an annular layered structure preform rod, whose core diameter and the relative refractive index difference between the core and the cladding are 4 ?m and 1.14 %, respectively. There can be 6 modes in total at a wavelength of 1.319 ?m and some of these modes couple with each other during propagation along the test fiber. The polarization behavior through the mode coupling is investigated theoretically and the axisymmetric birefringence of the test fiber is evaluated experimentally to be 4.1 × 10-5 from the fiber length dependence of the output light polarization state. This value is in good agreement with the theoretical value 4.7 × 10-5 estimated from the structural parameters of the preform rod from which the test fiber is drawn. The stress induced birefringence is also evaluated to be 5.9 × 10-8, which coincides with those of the standard single mode fibers and much less than the axisymmetric birefringence by three orders of magnitude.

Brillouin active fibers, based on stimulated Brillouin scattering (sBs), have been extensively studied as ambient sensors by exploiting quartz fiber intrinsic acoustooptic properties[5-7]. Thus, the fiber is inherently a sensor, as opposed to fiber Bragg gratings, in which lines have to be photolithographically etched on the fiber by UV light. The sBs threshold enables sensing to be switched on and off in standard communication fibers, leading to fiber dual use. They have also been examined as combined optical and acoustic waveguides for joint optical and acoustic sensing. Success of these sensors lies in lowering the sBs threshold to achieve low power, short fiber length and multi-Stokes line generation. Numerous schemes have been proposed and tested, such as fiber rings, and they will be surveyed. The inherent optical feedback by the back-scattered Stokes wave leads to instabilities in the form of optical chaos. This paradigm of optical chaos serves as a test for fundamental study of chaos and its suppression and exploitation in practical application in communication and sensing.

The time-division multiplexing of polarization-insensitive fiber optic Michelson interferometric sensors (TDM-PIFOMI) with compensating interferometer is presented. The crosstalk of lead fiber in a general time-division multiplexing of the fiber optic interferometric sensors is described and demonstrated. The experimental results match excellently with theoretical derivation. According to the experimental result and derived theory, only the induced phase signal of the sensitive lead fiber results in lead crosstalk , the sensing fiber of one sensor in the time-division multiplexing should not be placed on the effectively sensitive lead fiber of the other sensor to avoid the sensor crosstalk from lead crosstalk .

This paper described the distributed optical fiber temperature sensing system based on Brillouin amplifier structure, which combined Brillouin amplifier effect with optical time domain reflection(OTDR). With the relationship of temperature and stimulated Brillouin frequency shift, we can obtain the temperature on each point. Based on this principle, some experiments were taken, then the linear relationship and experimental data were given, which provided powerful foundation for future research.

As a developing novel technology recently distributed optic fiber temperature sensor has received considerable attentions. By optic fiber back spontaneity Raman dispersion phenomenon and OTDR theory, the system works. In this paper Rayleigh scattering curve demodulating anti-Stokes Raman scattering curve instead of traditional demodulation to mend SNR is adopted. And because of the differences of the two back dispersion parameter, wastage parameter and so on, signal groups grow indistinct by any demodulation method. Therefore, it is necessary for us to dispose micro-signal.

Screw assembly takes certain proportion in assembly work, and to achieve automatic screw flexible assembly is a difficulty in automatic flexible assembly system. In view of special requirements in robot screw flexible assembly, the paper proposes a new optic fiber sensing structure which detects the orientation and position errors of screws. The paper proposes a novel multi-optic-fiber-sensor measurement and treatment method based on SSPA that works under photoelectric diode electrical charge storage style and has high detecting sensitivity. At the same time, the multi-route signals going through the same SSPA apparatus make the system have higher capability/price ratio. As the signals are serially sampled in an instant by the same apparatus (SSPA), the measured object's actual situation is reflected and the influent factors such as changes caused in different time by light path and measured object are eliminated. And the precision of the sensor is also increased. A new method by changing clock frequency of SSPA and controlling the output of light source power is proposed to enlarge SSPA's detecting range. Through the treatment method of partitioning the multi-output BP network into several single-output ones and the subsection of variables' value between input and output, the dynamic capability is improved consumedly; At the experimental platform based on the opticfiber- sensing-technology the experiment successively accomplishes the initial screwing process of M8 screw and bolt with orientation warp of 0~100 and position error of 4—12mm. When the orientation warp is 9.24° and initial position error is 8.72mm, the time spent at initial screwing process is 20 seconds. If the pose warp is smaller, the time will be shorter.

In Japan, number of human lives and assets are being lost due to collapse of slopes at number of occasions during rainy season each year. Pleasantly, a main form of forecasts for such collapse of slopes consists of forecasts by precipitation. However, collapse of slopes can take many different shapes depending on the land formation, geological characteristics, vegetation, etc. and in some cases, a collapse happens with no relation to precipitation at all. Under such circumstances, there is an expectation for development of more reliable technology of slope collapse forecast. Based on this background, we developed our original technology, namely, optical fiber displacement sensors and slope monitoring system. We have been undertaking functional testing of this system since April 2001. We are currently collecting valuable data for building a system which shall enable us to give successful forecasts of collapse of slope. So far, successful forecasts using the system include detection of collapse of slope occurred in June, 2001.

This paper discusses the basic theory and structure of radiation temperature measurement instrument whose quartz optical fiber bundle couples directly with optic-electronic detector. The paper also presents theoretical analyses and experimental result, and proposes a concrete manner to increase the measurement precision of the instrument

Ultra-weak bio-chemiluminescence (UBC) from germinating soybean (Glycine max L. Merr) cotyledon under mechanical wounding was observed by a high sensitive single photon counter (SPC) device. SPC measuring results showed that the UBC intensity of wounding green cotyledon was very high firstly and reached to a stationary state after about 5 minutes. Wounding-induced emission could be suppressed by wounding treatment with sodium azide. While the intensity increase of the wounded etiolated soybean cotyledon was less than the green one. Deutenum oxide both amplified the emission intensity of green and etiolated. Singlet oxygen (102) is a main cause of the emission during the wounding phase. We suggested that the main process was probably that chioroplast and mitochondria damage at the wounded place and leaded to ROS generation, such as H202, 102 etc. The electronic excitation energy transfered from the excited molecules by ROS to Chl-a in the thylakoid membranes by way of relatively high quantum yields, so the intensity of UBC in the wounded soybean green cotyledon was obviously higher than in the wounded etiolated soybean cotyledon.

Fluorescence optical fiber sensor is one of the hot-spot problems in the field of modem optical fiber sensor technology. The concentration of measured materials is decided by measuring its special fluorescence spectrum. This paper presents a novel type of fluorescence optical fiber measurement system for measuring oil concentration in seawater, which combines fluorescence spectrum processing with optical fiber sensing technique. The basic principle and characteristic of fluorescence measurement method are discussed. The fluorescence specific properties of oil in seawater are analyzed. And then the total scheme of the fluorescence optical fiber measurement system is designed. According to the comparative study of energy spectrum distribution of light source, the pulse xenon lamp with UV spectrum, which has low-power consumption, high strength, and low-repeat frequency, is used as the excitation light source. And low-loss silicon optical fiber bundle has been used as transfer channel of light signal. We also redesign the optical fiber probe to effectively eliminate light noise and make seawater exchange real time. In order to effectively separate the fluorescence produced by oil in seawater and the scatter light from the exciting light, high block coefficient, narrow band interference filters are used as spectrum filters. The detecting method of double light route and double channel at the same time is used to eliminate the signal variation due to undulation of the exciting light source. Experiments indicate that the prototype processes many advantages, such as good relativity and repeatability, high-precision, good real time, and anti-jamming. It seems that it will get wide applications foreground in the field of environment measurement.

Because of cross sensitivity of multiple parameters and unknown dynamic environments, the data fusion used in optic fiber sensors is important. This paper describes a new distributed sensing system, which is used to solve this coupling problem in distributed optical fiber strain and temperature sensors. The sensors consist of fiber Fabry-Perot interferometers, and there are two Fabry-Perot interferometers in each position needed to monitor, one is for strain and temperature sensing, and another is only for temperature. Correspondingly, those sensors are distributed along two optical fibers and an optical time-domain reflectometer(OTDR) with dual-wavelengths is used to determine the trouble location and reflectivity of sensors. Then a data fusion mathematic model is established and applied to provide the precise information about strain and temperature of pipeline. Through this system, monitoring of the deformations of pipeline can be realized.

A fiber Bragg grating (FBG) sensor system for multi point, dynamic strain or temperature measurement is reported. The system uses a combination of an unbalanced fiber interferometer and phase locked loops and is capable of measuring dynamic signals with frequencies ranging from 100Hz to10kHz. Strain measurements with parallel FBG sensor arrays demonstrate strain resolution of better than 27.5n?/?Hz and measurement range of 0-3400?? at10kHz.

We propose and demonstrate a novel method of distribution sensing of Doppler-Shift frequency, by applying Synthesis of delta-function-like Optical Coherence Function (SOCF) to laser Doppler velocimetry. SOCF is a technique to resolve longitudinal position information along one arm of a laser-interferometric system. Distribution of the Doppler frequency is successfully measured in experiments.

Optical fiber sensors for the measurement of electric power are reviewed. We focus on the direct measurement approach, which allows electric-power-sensing signal to be directly obtained from light wave canier. Based on Pockels and Faraday effects, three kinds of optical electric-power sensors have been developed, including the combination of a Faraday medium with a Pockels medium in cascade; utilization of the single crystal exhibiting both Faraday effect and Pockels effect; and application of the electro-optic crystal multiplier. Potential applications of optical electric-power sensors lie in electric power industry and the field of electromagnetic compatibility. Measurement of active power, uncertainty and effects of temperature variations and vibration are key problems to be solved for optical electric-power sensor. Some corresponding solutions are proposed.