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.