In this paper, we report recent progress in long-period fiber gratings (LPFGs) fabricated by using a new writing technique that is mainly based on the thermal shock effect of focused high-frequency CO₂ laser pulses at several kHz. The writing mechanism of this technique is reported for the first time to our knowledge. Novel sensor systems for low-cost measurement of strain and dynamic transverse load are proposed and demonstrated. In addition, phase-shifted LPFGs are fabricated and used for sensing of strain and temperature. Finally, the etching characteristics of these LPFG sensors are investigated.

In this paper, a brief review of recent advances on high-temperature distributed fiber optic sensors is presented, which includes (1) background on fiber gratings, (2) in-fiber grating fabrication methods in single crystal sapphire fiber, (3) reflection-type fiber specklegram generated in single crystal sapphire fiber, and (4) preliminary experimental results on high temperature sensing.

A number of embedded sensor protection system (ESPS) and surface-mountable sensor protection system (SSPS) for fibre optic sensor (FOS) have been developed in this paper. Fibre Bragg Grating (FBG) sensor protected by the designed protections system have been used to monitor the cure progress and structural health status of concrete cylinders. Results indicate that the sensor protection systems for the FOS perform adequately and effectively in concrete environment. The protected fibre optic sensors are suitable achieve the structural health monitoring in practical. It is also revealed that there is excellent correlation between the results obtained from the protected FOS and reference electrical resistance strain gauges.

We present a simple technique for the interrogation of fiber Bragg grating (FBG) sensors using a self-seeded Fabry-Perot laser diode (FP-LD). The FBG sensor is configured in such a way that its reflection spectrum consists of two peaks, whose separation depends on the physical parameter to be measured. When the modulating frequency of the FP-LD is set properly, stable short pulses at the two wavelengths selected from the same FP-LD mode with the FBG are generated simultaneously. The wavelength separation of the dual-wavelength pulses is converted into a time difference by transmitting the pulses through a dispersive fiber. In this way, accurate wavelength measurement is replaced by the less expensive time measurement. To multiplex similar sensors that are sufficiently far apart spectrally, it is only necessary to change the modulating frequency of the FP-LD. To balance the pulse intensities at the two wavelengths for a particular sensor, the temperature of the FP-LD can be adjusted. Using this technique, we demonstrated experimentally a number of FBG-based sensors, including displacement/bending sensors, temperature-compensated current sensors, and transverse force sensors. This technique provides an intensity-referencing-free demodulation scheme, an easy way to interrogate a series of sensors, and an effective means to overcome drifts.

LPFGs written by high-frequency CO₂ laser pulses have great potential for use in optical fiber sensing and communication. It is of importance to study the fundamental characteristics of these novel LPFGs. In this paper, a more systematic analysis is carried out to investigate the resonant wavelength-bend sensitivity of the LPFG and its bend loss of resonant peaks based on the mode field theory. It is for the first time to our knowledge, that a method is proposed for analysis of the bend orientation-dependence of the LPFG. The simulation is in agreement with experimental results. This paper provides a more systematic analysis for the bending characteristics analysis of the LPFG written by the high-frequency CO2 laser pulses exposure method.

By using the edge-filtering approach, a low-cost strain sensor system with the long-period fiber grating (LPFG) written by high frequency CO₂ laser pulses is demonstrated for the measurement of both static and dynamic strains. In this system, the wavelength-shift induced by the strain applied to the LPFG is interrogated by using a single-frequency DFB laser source. The intensity change due to the wavelength-shift is received by a photodetector. In addition, the intensity fluctuation due to instability of the fiber link is compensated by using a reference light source at 1310nm. In the static measurement, the result shows that the relationship between the electrical output of the sensor and the strain is very linear. The resolution of this sensing system is better than 10με and the error is ±10με. Dynamic strain measurement over 5kHz is also demonstrated. This sensor system offers the advantages of low-cost and fast response.

A low-cost fiber optic sensor system based on multimode fiber and an LED light source is presented. A multimode fiber Bragg grating (MMFBG) element is used as a strain sensor. In a matched grating scheme, a MMFBG similar to the sensing one was used as a reference in the receiving unit. For detection of large wavelength shift we demonstrated the feasibility of MMFBG wavelength detection using a single mode fiber fused coupler edge filter. The high cost normally associated with wavelength interrogators for single mode fiber FBG sensors was overcome by the utilization of a low cost multimode fiber pigtailed LED light source. The multimode fiber sensing system has the potential of maintaining much of the advantages of its single mode FBG sensor system counterparts. The MMFBG sensing schemes could be used for short distance, high sensitivity, high speed, strain, temperature and acoustic sensing applications

A novel fiber Bragg grating (FBG) sensor for the measurement of high temperature is studied. The sensing head is comprised of one FBG and two metal strips with different lengths and different coefficients of thermal-expansion (CTE). The temperature to be measured can be converted into the strain of the FBG. One can know the temperature according to the peak wavelength shift of the FBG induced by the strain. A dynamic range of 800°C and a resolution of 1°C can be obtained by this sensor system. The experiment results well agree with the theoretical analysis.

This paper reports the development of a wavelength detection system that can be used to detect the Bragg wavelength of fiber Bragg grating sensors. The system can interrogate up to 100 sensors with wavelength detection resolution on the order of picometers. The results of medium-term test will be reported. Possible applications will be discussed.

With decades of research experience on optical sensors, Optoelectronic Technology Lab of Chongqing University (OTLCU) has studied on a variety of sensors system designed for practical use in health monitoring. In OTLCU, embedded and surface mounted fiber Fabry-Perot strain sensor has been developed for monitoring the local strain of both concrete and steel truss bridge. Optoelectronic deflect meter, with a group of optical level sensor in a series connected pipe, was developed for deflection monitoring and line shape monitoring of the bridges. Laser deflect meter, with a laser pointer and a sensors array, has been also developed for a dynamic deflection monitoring of the bridges. To monitoring the 2-Dimentional displacement of the bridge, a self-calibrating imaging system was developed. All these sensor systems have been applied in different bridges successfully. This paper briefly describes principle of these optical sensing systems, and also gives some representative results of the system in practical application of bridges.

Historically, due to the high cost of optical devices, fiber-optics sensor systems were only employed in niche areas where conventional electrical sensors are not suitable. This scenario changed dramatically in the last few years following the explosion of the Internet which caused the rapid expansion of the optical fiber telecommunication industry and substantially driven down the cost of optical components. In recent years, fiber-optic sensors and particularly fiber Bragg grating (FBG) sensors have attracted a lot of interests and are being used in numerous applications. We have conducted several field trials of FBG sensors for railway applications and structural monitoring. About 30 FBG sensors were installed on the rail tracks of Kowloon-Canton Railway Corp. for train identification and speed measurements and the results obtained show that FBG sensors exhibit very good performance and could play a major role in the realization of "Smart Railway". FBG sensors were also installed on Hong Kong's landmark TsingMa Bridge, which is the world longest suspension bridge (2.2 km) that carries both trains and regular road traffic. The trials were carried out with a high-speed (up to 20 kHz) interrogation system based on CCD and also with a interrogation unit that based on scanning optical filter (up to 70 Hz). Forty FBGs sensors were divided into 3 arrays and installed on different parts of the bridge (suspension cable, rocker bearing and truss girders). The objectives of the field trial on the TsingMa Bridge are to monitor the strain of different parts of the bridge under railway load and highway load, and to compare the FBG sensors' performance with conventional resistive strain gauges already installed on the bridge. The measured results show that excellent agreement was obtained between the 2 types of sensors.

Optical fiber sensors have received increasing attention in the fields of aeronautic and civil engineering for their superior ability of explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment. In this paper, a novel FBG (fiber Bragg grating) strain sensor, which was packaged in a 1.2mm stainless steel tube by epoxy resin, was developed. Experiments were conducted on the universal material testing machine to calibrate its strain transferring characteristics. The sensor has the advantages of small size, high precision and flexible use, and demonstrates promising potentials. Ten of tube-packaged strain FBG sensors were applied in the vibration experiment of submarine pipeline model. The strain measured by FBG sensor agrees well with the electric resistance strain sensor.

Quasi-static testing of the fabric material mechanically with a novel embedded strain measurement system, which aimed at mechanical analysis of the dynamic characteristics of the parachute canopy textile with fiber optic technology, and using a tensile tester were aimed at correlating the results obtained by using the fiber optic sensors to the mechanical parameters, and in calibrating the system. To achieve better and more consistent results, FBG sensor took part in fabric samples testing in the warp, fill, and 45° directions. The mechanical tensile tests provided a traditional correlation between the loads and the elongation of the fabric structure, and were correlated to the fiber optic sensor output calibration. The comparison shows clearly that the two curves converged in the loading region before the structural failure started. The achieved results were consistent with each other, which dues primarily to the consistency in the fiber embedded technique, and will be discussed in detail in this paper.

In order to improve the initial and the response times of the Laser Dew-Point Hygrometer (LDH), the measurement simulation was developed on the basis of the loop computation of the surface temperature of a gold plate for dew depostition, the quantity of deposited dew and the intensity of scattered light from the surface of the plate at time interval of 5 sec during measurement. A more detailed relationship between the surface temperature of the plate and the cooling current, and the time constant of the integrator in the control circuit of the LDH were introduced in the simulation program as a function of atmospheric temperature. The simulation was more close to the actual measurement by the LDH. The simulation results indicated the possibility of improving both the times of teh LDH by the increase of the sensitivity of dew and that of the mass transfer coefficient of dew deposited on the plate surface. It was concluded that the initial and the response times could be improved to below 100sec and 120 sec, respectively in the dew-point range at room temperature, that are almost half of the those times of the original LDH.

We develop a simple strain sensor using polymer optical fibre Bragg grating and long period fibre grating. The sensor head is formed by a polymer optical fiber Bragg grating. A long period fibre grating is used for strain related wavelength shift demodulation. This particular combination of two quite different gratings could offer very large dynamic, up to tens of thousands micro-strains, for strain sensing. The preliminary experimental results have demonstrated that this sensing scheme provides good linearity, high resolution and large dynamic range.

In this paper, the rule of transmission characteristic of Photonic Crystal Fiber (PCF) is discussed when it is injected with different kinds of medium and stressed. Based on Finite-Different Time-Domain (FDTD) algorithm, the Maxwell equation group that changes in time-domain can be transformed into different equation on Yee Lattice. Absorbing boundary condition is added in proper position around the lattice, in order to truncate the algorithm space, and to transform the electromagnetic problem with infinite extending structure into the one with finite extending structure. Through simulating the photonic field distribution of PCF in this way, the transmission characteristics of PCF which is different from the ordinary optic fiber can be gotten. When the medium in the air holes changes, for example, they are injected with gas or liquid that has special refraction index, strong interaction will be brought about between the medium and the light that has conduction mode. In this article, the rule of transmission characteristic of PCF is analyzed, when PCF is stressed and injected with different kinds of medium.

Chlorine content in drinking water is hazardous for health. In this presentation a fiber optic evanescent field absorption sensor is demonstrated which can be implemented for the detection of the content of chlorine in drinking water. The method of demonstration is based on the absorption of evanescent waves through the development of color, which is achieved due to the reaction of diethyl phenylene diamine with chlorine present in water. A bent U-shaped probe is implemented in order to improve the sensitivity.

A dual-parameter optical sensor has been realized by UV-writing a long-period and a Bragg grating structure in D-fiber. The hybrid configuration permits the detection of the temperature from the latter and measuring the external refractive index from the former responses, respectively. The employment of the D-fiber allows as effective modification and enhancement of the device sensitivity by cladding etching. The grating sensor has been used to measure the concentrations of aqueous sugar solutions, demonstrating the potential capability to detect concentration changes as small as 0.01%.

As a chemiluminescence (CL) probe, 3,7-dihydro-6-{4-{2-(N’-(5-fluoresceinyl) thioureido)ethoxy}phenyl}-2-met -hylimi-dazo{1,2-a}pyrazin-3-one dosium salt (FCLA) can sensitively and specifically react with singlet oxygen (¹O₂ ) and superoxide(O₂""). BSA (Bovine Serum Albumin) can enlarge the CL intensity of FCLA to 860%. This report presents a novel method for determination of Aflatoxin B1 (AfB1) mediated by FCLA+BSA. The concentration of AFB1 showed an obvious positive correlation with the CL intensity mediated by FCLA+BSA. This method could measure accurately ng/ml of AfB1 concentration. At the same time, the fluorescence spectrum of FCLA+BSA and FCLA+BSA+AfB1 were measured respectively, which showed that the fluorescence intensity of FCLA+BSA+AfB1 was higher than FCLA+BSA. Comparing the peak value of FCLA, FCLA+BSA and FCLA+BSA+AfB1 had a 6nm Einstein shift (red shift). The study suggested that CL method mediated by FCLA+BSA might be applicable to the determination of AfB1 concentration.

To realize the on-line fluorescence monitoring of mineral oil pollution in water, three-dimensional spectral characteristic of oil-water intermixtures must be studied and the characteristic must be extracted. Using excitation wavelength, fluorescence wavelength and fluorescence intensity as three-dimensional system of coordinate, through sampling and surface fitting, three-dimensional fluorogram is gotten, which can provide gist for oil discrimination when presented in contour chart (finger-print map of oils). But there is little difference between characteristics of three-dimensional fluorogram because of the similarity of constituent and structure of similar oils. Therefore this paper introduces quantitative analysis method-characteristic parameter method which starts with analyzing statistical characteristic of three-dimensional fluorogram. Using RFPC fluorescence spectrometer (Shimadzu, Japan), three-dimensional fluorescence spectra of diesel oil, machine oil, gasoline oil, crude oil are measured and parameterized. The result shows that as a quantitative classified discrimination method of three-dimensional fluorescence spectra, the parameter of characteristic parameter method possesses definiteness for three-dimensional fluorescence spectra, and it is applicable, available when used in oil discrimination.

By dividing both the object and reference beam in an OCT interferometer, two independent OCT imaging channels are assembled. The depth scanning proceeds simultaneously in the two OCT channels and from the same range, however a differential optical path difference can be introduced between the two channels. In this way, two simultaneous images are generated where the depth differs in each pixel by the differential optical path difference. A dual OCT system working at 850 nm was devised and we demonstrate the capability of the method by simultaneously acquiring images from the optic nerve and fovea of a volunteer. The configuration devised insures a strict pixel to pixel correspondence between the two images irrespective of the axial eye movements while the depth difference between the corresponding pixels is exactly the differential optical path difference. The images are collected by fast en-face scanning (T-scan) which allows both B-scan and C-scan acquisition.

A Surface plasmon resonance (SPR) biosensor constructed with common path, heterodyne inteferometric system has been developed. The sensor ship consists of a BK7 substrate coated with gold film on which the receptor of the specific biomolecular or protein has been immobilized. The light source consisting of the s and p polarizations with heterodyne frequency of 60kHz is used to measure the phase difference between these two polarizations. Because the SPR sensor probes the changes of refractive index near the gold film (i.e. about one wave-length), the more the binding of molecules on the sensing surface results in the less sensitivity of the detection. In order to overcome this shortage, we set two quarter-wave plates before and after the SPR prism to make the sensitivity of measurement to be tunable. This sensor could detect the concentration of antibody of sheep IgG as low as several nanograms per milliliter. The results indicate that this system provides high sensitivity and is capable for detecting biomolecular interactions.

With high-sensitivity single-photon counter, spontaneous chemiluminescence (CL) spectrum and different temperature study on rice (Oryza sativa L.) seeds during early imbibition were carried out. The emission spectrum of whole rice seed, rice and coat had a greater proportion of red light during early imbibition. Comparing with spontaneous CL of barley (Hordeum vulgare L.) and soybean (Glycine max L. Merr) seeds, the spontaneous CL of rice seeds had a nonlinear, logarithmic-like increase of intensity in the T range 30-50°C, the Van't Hoff coefficient Q10=IT+10/IT is equal to 2, which led us to the conclusion that spontaneous CL of rice seed during early imbibition partly came from enzyme catalyzing chemistry reaction.

A 30km long distance distributed optical fiber Raman temperature sensor (DOFRTS) system has been made, it use new measuring temperature principle of optical fiber amplified anti-Stokes Raman spontaneous scattering. In the system, 1550nm erbium-doped optical fiber laser, a highness speed data acquisition card and signal processing technique are used. By using these technique, the problem of weak signal detection is resolved and signal to noise ratio is increased. All components of system are put into an intellectualized constant temperature box and work in constant temperature condition. Stability and environment adaptability are improved. By appraisal, performance of the system is listed as follows: length of single mode fiber: 31km, temperature rang:0-100°C (can be expanded), temperature measuring uncertainty:±2°C, temperature resolution:0.1°C, measurement time:432s, spatial resolution :3m.

In order to demodulate frequency division multiplexed optical fiber Fabry-Perot sensors with high accuracy and absolute cavity length, an improved cross-correlation method was presented. As the applying of a special correlating factor in it, the cross correlation function at every sensor's cavity length is a single peak and multiplexed sensors that cavity length is close to each other can be easily distinguished, and segment golden search method was employed to reduce computation and demodulating speed is fast. The multiplexing experiment of two sensors was accomplished with the help of general demodulating system constituted by broadband light source, spectrometer etc. The results showed that the system can demodulate the frequency division multiplexed signal of optical fiber Fabry-Perot sensors, and the least cavity length difference that can be distinguished among multiplexed sensors is less than 6μm and fluctuation of the cavity length is less than 0.073%.

Due to their variability Fibre Bragg Grating (FBG) sensors are introduced in a growing number of applications. Furthermore using their spectral selectivity and adjustable reflectivity these sensors are predestined for serial networking, whereby presently in most cases the addressing is realised by time division multiple access (TDMA) or wavelength division multiple access (WDMA). But these technologies have big disadvantages regarding the effective use of the prevailing resources time and wavelength, respectively. In this paper a new scheme capable of addressing a large number of FBGs in a single serial network is proposed and compared to TDMA and WDMA. Using all optical sequence inversion keyed (SIK) direct sequence (DS) code division multiple access (CDMA) it overcomes the restrictions handling the resources time and wavelength without loosing accuracy. A simulation with 20 FBGs in a spectral range of 2nm shows the abilities of this system, which can be build up with nearly the same components as TDMA systems.

In order to increase the number of channels available to a grating based strain sensor system specialised gratings were designed that would allow the sensor system to be able to distinguish between a number of gratings located in the one WDM channel independently of the amount by which they overlap each other in the wavelength domain. Distinguishing between gratings is achieved by inscribing a carrier frequency in the grating spectrum, so that each grating can be addressed in the Fourier domain via the spectral information centred around the inscribed carrier frequency. Tests performed on the gratings successfully show the ability to distinguish between three spectrally overlapping gratings. The calculated value for Young's modulus, 72+/-3GPa, was found to be in keeping with the standard value of 70.3GPa for fused silica.

Fiber Bragg grating (FBG) sensing is gaining attention in both scientific research areas and engineering applications thanks to its distinguishing advantages including wavelength multiplexing capability, miniature size, high sensitivity, immunity from electro-magnetic interference, etc. FBG sensing is based on the detection of the shifted Bragg wavelength of the light reflected by a fiber grating which is sensitive to various physical parameters such as strain and temperature. One of the challenging tasks in FBG sensing is to determine the Bragg wavelength shift, which can be done by using an optical spectrum analyzer (OSA). An OSA is suitable for laboratory tests, but not an ideal solution for field applications in term of cost and convenience. Different wavelength demodulation methods have been developed for FBG sensing purpose. One of them is employing a bulk linear edge filter to convert the wavelength shifts to intensity variations. This method offers several obvious advantages including low cost and ability for dynamic measurements. However, most of the edge-filter based FBG sensing systems are designed for single-channel measurement. In this study, we propose and develop a multi-channel FBG sensing system based on the edge-filtering technique. In order to demodulate multi-channel signal from FBG sensors, we propose to use a dense wavelength division multiplexing (DWDM) module. The light signals coming from wavelength-multiplexed FBG sensors are demultiplexed into individual channels and demodulated by the pass-band edges. In the present study, a four-channel FBG sensing system has been demonstrated.

In this paper, a novel method for multiplexing extrinsic fiber Fabry-Perot interferometric sensors (EFPIs) using the coarse wavelength-division-multiplexing technology (CWDM) is proposed and demonstrated, for the first time to our knowledge. The system and principle for sensing and multiplexing are described. A 1×4 CWDM is used to multiplex signals from four EFPIs with identical cavity length. The experimental results show that a strain accuracy of 2.5me is achieved. There is little cross-talk between adjacent sensor channels. This system improves the multiplexing capability of EFPIs by a factor of four. It is anticipated that such a sensor system could find important applications in smart materials and health monitoring for large structures.

The spatial resolution of a 30km distributed optical fiber sensor is optimized to 3m. Two methods to measure the spatial resolution of distributed optical fiber sensor were demonstrated. The lower limit of the spatial resolution of the system is determined by the width of the input laser pulse. The bandwidth of optoelectronic receiving system and the electronic system also affect the spatial resolution of the system. The bandwidth of the electronic system shall be matched with the pulse width of the laser. The spatial resolution of system can be measured directly or evaluated indirectly by the half width of the Fresnel reflection at the end of the fiber. The spatial resolution of the system reached 3m after the optimization.

This paper demonstrates the recent achievements in the field of Brillouin based distributed optical fiber temperature sensing. When a dispersion-shifted fiber was subjected to a temperature cycle between 20 and 820 °C, the Brillouin shift exhibited an undesired hysteresis with a maximum frequency discrepancy of larger than 48 MHz between heating and cooling processes. After the fiber was annealed for 9 h at 850 °C, however, the hysteresis almost disappeared for repeated temperature cycles in the ranges of 20-820 °C and of 500-800 °C with deviations of the measurements from the best-fit curve of less than ±12.5MHz. The temperature dependence of Brillouin shift in the range of 20-820 °C in the annealed fiber was well expressed by a second order function of temperature. A sensing scheme that utilizes both output signals of the fiber Mach-Zehnder interferometer used as an optical frequency discriminator has been proposed. The scheme that has the advantages of less system adjustment and fast measurement, combined with a suitably annealed fiber, offers a reliable means for the Brillouin shift-based distributed sensing over the wide temperature range.

This paper firstly introduces the principle of distributed sensing system based on Polarization sensitive Optical Time-Domain Reflectometer (P-OTDR). As known, the change of State of Polarization (SOP) in fiber is sensitive to environment, consequently this sensing method can extract very little perturbation of extra temperature or strain; another significant advantage is that the sensing information can be achieved nondestructively at one end. Hence, this technique has become a practical and helpful tool in distributed optical fiber sensing system. However backscattered light in single-mode fiber is very weak, and the optical pulse width limits the spatial resolution, so there is a compromise between SNR and sensor spatial resolution. We investigate two signal-process methods to extract the state polarization (SOP) evolution from backscatted signal. From the experiment results, we find that both the digital average and deconvolution can be used for enhancing SNR and system spatial resolution. And we also find hundred of digital average is enough, the more time we average the less improvement of SNR we get. At the same time, we view that the SOP of backscattered signal is the response of sensing system. By mean of deconvolution the actual SOP evolution is not lost, and the spatial resolution of POTDR System doesn’t degrade with a wider pulse. Compared with previous deconvolution case, the deconvolution method can effectively improve the system spatial resolution without decreasing the transmitting pulse width. Finally we give some experiment results with strain perturbation, our system can detect the point where the environment changes, which is suitable for smart structure and optic-fiber sensor application.

Laser interferometers with better than10 picometer (pm) accuracy in displacement measurement and 1-3 microns in absolute distance ranging accuracy are sought in several of NASA's planned missions, such as the Space Interferometry Mission (SIM) and Terrestrial Planet Finder (TPF). Over the past several years, we have made significant progress at JPL toward a laser heterodyne interferometer system that can provide both picometer displacement measurement and micron level absolute distance measurement. This paper presents an review on the development of high precision metrology gauges for these missions.

A Michelson based fiber optic low-coherence interferometric quasi-distributed sensing system permitting absolute length measurement in the sensors array is proposed. The main part of the sensing system is a fiber optic 3x3 star coupler. The architecture of the fiber optic sensors can be easy realized as a linear sensor array, twin sensor arrays or a loop sensor array. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application could be deformation sensing in smart structures. Experimentally, a 6 sensors array has been demonstrated.

We demonstrate a method of displacement measurement based on polarization hopping of laser with optical feedback. The measurement system is composed of a half-intracavity He-Ne laser, a quarter wave plate and an external feedback mirror. When the conditions of the second polarization flipping are satisfied, the frequency of intensity modulation can be doubled, and one polarization switching corresponds to displacement of external mirror. Meanwhile, the intensity transfer between two polarization states will come out, i.e., an increase of one polarization light intensity always accompanies a decrease of another polarization light intensity. One period of intensity transfer can be divided into four domains: e-light, e and o-light, o-light, and no light, and each domain corresponds to change of external cavity length. According to appearing sequence of the four domains, the movement direction of external mirror can be distinguished. Our method can improve the resolution of displacement measurement 8 times that of conventional optical feedback, and reaches 40nm for a laser wavelength of 632.8nm.

Most fiber optic interferometric refractometers suffer from large temperature sensitivities, especially those that employ long-period gratings. This paper presents results on a compound-cavity Michelson interferometer whose phase shift is only dependent on the refractive index of the analyte surrounding the fiber probe. This single probe Michelson interferometer uses mode coupling in a long-period grating to establish the two optical paths in a single fiber, and therefore presents a compact sensor for measuring the refractive index and other related properties (such as chemical concentration and composition) of various types of substances. It can also be used to measure the level of liquid in a container. Experimentally, we measured a phase change of 1.374 rad for a change in refractive index of 0.0132. The temperature sensitivity of one such compensated device is only -0.01 rad/°C, which is less than the temperature gradient of the refractive index of solutions of glycerine in water.

The Space Interferometer Mission (SIM), scheduled for launch in 2009, is a space-born visible light stellar interferometer capable of micro-arcsecond-level astrometry. The Micro-Arcsecond Metrology testbed (MAM) is the ground-based testbed that incorporates all the functionalities of SIM minus the telescope, for mission-enabling technology development and verification. MAM employs a laser heterodyne metrology system using the Sub-Aperture Vertex-to-Vertex (SAVV) concept. In this paper, we describe the development and modification of the SAVV metrology launchers and the metrology instrument electronics, precision alignments and pointing control, locating cyclic error sources in the MAM testbed and methods to mitigate the cyclic errors, as well as the performance under the MAM performance metrics.

A novel method for multiplexing fiber-optic Fizeau strain sensors with optical amplification is proposed and demonstrated. This method overcomes the two intrinsic disadvantages of fiber-optic Fabry-Perot (F-P) strain sensors, i.e. weak signal and difficult multiplexing. The amplified spontaneous emission (ASE) and optical amplification of an Erbium-doped fiber (EDF) pumped by a 980nm laser diode are used simultaneously to enhance the interferometric signal considerably. A Fizeau interferometer formed by two fiber ends with a quite different reflectivity is used to replace the F-P cavity in sensor head design. Such a Fizeau cavity can enlarge the cavity length by at least an order of magnitude and allows more than ten sensors to be multiplexed simultaneously by using spatial-frequency multiplexing. The operating principle of the sensor system is discussed and an experiment is carried out to verify the concept of the method proposed. It is anticipated that such a sensor system could find important applications for health monitoring of large structures.

A novel scheme of a fringe count interferometric accelerometer is proposed. In view of practicability, the sensor must be made up of only fiber. Two 3dB directional couplers and singlemode fibers are used in this scheme to compose an imbalance Mach-Zehnder interferometer. Phase modulation is achieved by modulating LD frequency to scan the interference fringes. With special technique, only one PIN is needed to count and identify the moving direction of the interference fringes. The signal can be transmitted more than several kilometers in a pair of fibers. The two arms of the interferometer work at push-pull mode, which is favorable for temperature compensation. The resolution is significantly improved by fringe sub-division. A real-time dynamic vibration signal can be measured without distortion by this system.

With the development of the technique of the digital signal processor, the using of digital signal processor in the open loop IFOG (interferometric fiber optic gyroscope) signal processing brings a great improvement of the performance of IFOG, especially in the technique of digital filtering, acquisition the values of arcsine and inverse tan function. The traditional way to get the values of inverse tan function is linear interpolation technique in digital signal circuit. This article put forward a new way to acquire the values of inverse tan function, the proportion of the second order Bessel function to the first order Bessel function and the proportion of the fourth order Bessel function to the second order Bessel function by using of the virtue of DSP, high speed of data processing. The fundamental, second and fourth harmonic signals from photoelectrical detector are sampled and demodulated by analog circuit. Then the signals from analog circuit are sampled into DSP by a 24-bit analog-to-digital converter, which is used to improve the dynamical range of the system. Then DSP computes the values mentioned above by polynomial approach. The simulation in Mathematic and Microsoft Visual C++ 6.0 proved that the method of polynomial approach to the functions has higher precision compared to the method of linear interpolation. Meanwhile the designed circuit shows it can meet the demand of real time data process. The tested results of designed circuit prove it has a great improvement in the dynamic range and precision of IFOG.

The combined two-ring-resonator schemes of fiber optic gyroscope are developed and demonstrated. The two-ring topology structure has been classified 2 kinds: two-ring in series and in parallel. The cavity lengths L1 and L2 of the two-ring-resonator are chosen as 623m and 1260m, respectively. A theoretical model of the two-ring Rayleigh backscattering fiber optic gyroscope which including the Sagnac effect is established. The experimental results are agreement with the theoretical prediction.

Fiber Ring Laser Gyroscope (FRLG) is a novel resonant gyroscope which uses erbium-doped optical fiber as the gain medium and optical fiber as the ring resonant cavity. FRLG have advantages over conventional Interferential Fiber Optical Gyroscope (IFOG) with its simplicity in both the optical configuration and the electronic signal processing. The precision of FRLG depend on the linewidth of fiber ring laser output. So how to get narrower laser linewidth is key technology for FRLG. According to recently report, FRLG's laser linewidth reach 100 kHz, can not directly applicable to rotation sensing at present. A Stand-wave in the un-pumped erbium-doped fiber can induce self-written fiber grating, which have self-adaptable narrow band pass characteristics. Base on this, we propose a novel FRLG's structure. Two filter sections were used in this structure to make sure FRLG run in narrow linewidth and single mode. Fiber circulator, un-pumped erbium-doped optical fiber and Bragg grating (FBG) as the reflect mirror make up of the filter section. In this paper, we have optimized the parameters through a computing simulation. The theoretical and experimental study on FRLG has been finished. We get experimental results from them. FRLG which use this structure can get bidirectional laser output, the linewidth of laser can reach about tens kHz level and the power of laser output can reach 1dbm.

Re-entrant fiber optic gyroscope (Re-FOG), using a shorter Sangnac sensitive ring (SSR), makes the two counter-propagandizing lights re-enter the ring before they interference with each other when they reach the photo-detector. By this means, the Re-FOG gets the same detecting accuracy as the conventional interferometric fiber optic gyroscope (IFOG) that has several times length of the sensitive ring. In this paper, the principle of the Re-FOG is first reviewed. Then the output signal is analyzed. Finally a method of signal detection is presented.

A double-pass super-fluorescent fiber source with a wavelength-selective reflector fabricated using thin film filter technology was demonstrated. The simulation on output power and bandwidth and meanwavelength were made. The optimized parameters have been obtained and the desired reflector has been fabricated. A practical prototype was made and tested, its output power is great than 8.5 mW, the bandwidth is great than 28nm. The instability of power and meanwavelength are less than 3% and 3ppm/°C within -40 °C ~+60 °C temperature range respectively.

Torque sensing on rotating shafts is important for monitoring electrical and internal combustion machines, especially for real-time computer control. Optical fiber sensors are ideally suited to this application because of many desirable properties such as immunity to electromagnetic interference, their multiplexing capability and small size. This paper discusses a dual fiber Bragg grating sensor for the independent measurement of temperature and torsion in a rotating shaft. It shows theoretically that whereas torsion affects the differential wavelength of the gratings in the proposed configuration, temperature changes in principle only the common-mode wavelength. These characteristics of the system allow one to measure both torsion and temperature with the same sensing system. For the particular system investigated experimentally, the differential wavelength change was 19.4 pm/Nm, and the corresponding temperature sensitivity was -0.67 pm/°C. In contrast to these values, the temperature sensitivity of the common-mode wavelength was 25.4 pm/°C, and its torque cross-sensitivity was -0.19 pm/Nm.

In many industrial systems, the sensor is desirable to directly respond to a vector component associated with some physical phenomenon, such as the acceleration, velocity or displacement. This paper focuses on the application of fiber-optic accelerometers in oil well logging, presents a new design utilizing the combination of bellows structure and compliant material to enhance the unidirectional response of the fiber optic accelerometer. Furthermore, we accomplished a three components (3-C) acceleration sensing system by multiplexing three unidirectional sensing elements. Theory and experimental results show that our sensor can fulfill the demand of application in oil well logging, including responsivity, operation frequency range and directivity. The demodulated signal and the acceleration of vibration measured exhibit a linear relationship, and the suitable measurement frequency range of the system is between 3Hz and 800Hz. The on-axis sensitivity, cross-sensitivity and minimum detectable level is -101dB re V/ug, -135dB re V/ug and 39.3ug/Hz1/2, respectively.

A robust-fusion optic fiber sensor technology of proximity distance and orientation integration is studied in this paper. A novel optic fiber sensing head with redundant information, which can measure distance and orientation in any pose as well as compensate fluctuation caused by changing parameters such as surface reflectivity, light intensity and characteristic shifting from photoelectric-converter device, is proposed. The implement method of sensor network compensation is introduced. An improved BP network arithmetic, which can enhance the dynamic characteristic and measurement accuracy of the sensing system, is presented. To speed up the convergence rate of BP network training, GA -BP training method is applied. An intelligent signal detecting and processing system based on DSP is designed, the strong data processing ability of DSP makes the system hardware structure simplified. The method of moderate output light power control is put forward for enlarging the measuring range. Experiment result shows that robust-fusion optic fiber proximity sensor system has the distance measuring range of 0.1~19.9mm and the orientation measuring range of 0~25°. The measuring time of each point is 92.5ms.

A miniature optical sensor for laser particle counter is described, and some calculated and test results are reported in this paper. A reflective spherical mirror coated with highly reflective optical film is applied as collecting element for scattered light, and a PIN photodiode with high performance is used as the photo-detector. A band-pass preamplifier is used to eliminate lower-frequency electromagnetic interference from external environment, as well as to filter high-frequency components from electronic noise. An air sampling system can provide a very constant flow rate. The smallest particle diameter of the optical sensor is 0.3 microns with a signal-to-noise ratio exceeding 2:1.

A novel optical fiber null coupler (OFNC) sensor based on acousto-optic interaction is developed, which can be used in the structure health monitoring of the medical materials. The OFNC sensors can be response to 10MHz supersonic wave, and their signal-to noise ratio are higher then Piezo Ceramic Transducers(PZT). A kind of Perspex with a 1mm hole is employed as the sample, where the OFNC sensor is glued on, and the reflected signal of ultrasonic wave by the hole is detected .

A fiber thermometer using the cross detection of the fluorescence lifetime and blackbody radiation was presented to measure temperature from -10°C up to 1400°C. Using a long pure YAG crystal fiber as the seed and a 0.1 at. % Cr₂O₃-doped Y₃Al₅O₁₂ sintered powder rod as the source rod, a YAG fiber thermal probe with Cr³⁺ -ions doped end was grown by laser heated pedestal growth method. A blackbody cavity was constructed by sintered a thin ceramic layer around the Cr³⁺: YAG fiber end. A phase-locked detection scheme was used for the fluorescence lifetime detection. The fluorescence characteristics of the Cr³⁺-ions doped YAG was analyzed in a temperature range from -10°C up to 500°C. From 350°C to 1400°C the blackbody radiation signal in a narrow waveband were detected. Because the fluorescence lifetime was intensity independent, it should have the long-term stability and would not change if the fiber connectors of the probes were realigned. So the fluorescence lifetime based temperature measurement could be used to recalibrate that based on the blackbody radiation detection. Preliminary experimental results showed that the system could achieve a resolution much better than 1°C over the whole temperature range from -10°C to 1400°C.

The present work reports the design and implementation of an optical-sensor based virtual instrument for visualizing and estimating the degree of corrosion of metal surfaces exposed to atmosphere. A platform carrying the specimen plates was driven by a stepper motor assembly horizontally in XY directions. An opto-electronic transmitter-receiver unit was fixed vertically very close to the platform so that the sample surfaces may be scanned by a light beam. The reflected and scattered optical signals from each point in the scanned area were acquired by the sensor module. A parameter incorporating the relative values of these signals proved to be a fairly reliable measure of the surface texture, which in turn consistently represented the degree of corrosion. These signals interfaced with a personal computer enabled 3D visualization of the magnitude of the corrosion level of the surface and 2D mapping of the surface corrosion.

In order to successfully implement the extended-life operation plan of the nuclear power plant (NPP), predictive maintenance based on on-line monitoring of deteriorated components becomes highly important. Pipe wall-thinning is usually caused by Flow-Accelerated Corrosion (FAC) under the undesirable combination of water chemistry, flow velocity and material composition. In order to increase the confidence of understanding on underlying process, a multi-disciplinary approach has been adopted in this work. Here, we apply a combination of several advanced sensors, ranging from chemical electrodes to mechanical vibration sensors to monitor the thickness change of the elbow, which can be still economical option. Electrochemical Corrosion Potential (ECP) and pH are chosen as electrochemical parameters, the change of vibration mode, displacement, and etc. are chosen as mechanical parameters to monitor the wall thinning phenomena. Electrodes are developed for the on-line monitoring of pH and ECP. Vibration is considered as a promising candidate as a mechanical parameter. Various sensors are surveyed and some are chosen based on FEM analysis result, which shows the approximate vibration range according to the thickness change. Mechanical sensors need to be sensitive enough to detect small thickness change with adequate safety margin to a pipe rupture. A few sensors are suggested to detect vibration or displacement quantitatively. Fiber optic sensors are chosen for their non-contacting property, which is appropriate for the high temperature application. Accelerometer and capacitance gage are suggested for their applicability fit to the test purpose.

Low-loss optical wave guiding along a subwavelength-diameter silica wire leaves a large amount of the guided field outside the solid core as evanescent wave and at the same time maintains the coherence of the light, making it possible to develop sensitive and miniaturized optical sensors for physical, chemical and biological applications. Here we introduce, for the first time to our knowledge, a scheme to develop optical sensors based on evanescent-wave-guiding properties of subwavelength-diameter wires. Optical wave guiding properties of these wires that are pertinent to a waveguide sensor, such as single-mode condition, evanescent field, Poynting vector and optical loss are investigated. By measuring the phase shift of the guided light, we propose a Mach-Zehnder-type sensor assembled with two silica wires. The sensitivity and size of the sensor are also estimated, which shows that, subwavelength-diameter silica wires are promising for developing optical sensors with high sensitivity and small size.

Hybrid-integrated Optical acceleration seismometer and its digital signal processing system are researched and developed. The simple system figure of the seismometer is given. The principle of the seismometer is explicated. The seismometer is composed of a seismic mass,Integrated Optical Chips and a set of Michelson interferometer light path. The Michelson Integrated Optical Chips are critical parts among the sensor elements. The simple figure of the digital signal processing system is given. As an advanced quality digital signal processing (DSP) chip equipped with necessary circuits has been used in its digital signal processing system, a high accurate detection of the acceleration signal has been achieved and the environmental interference signal has been effectively compensated. Test results indicate that the accelerometer has better frequency response well above the resonant frequency, and the output signal is in correspondence with the input signal. The accelerometer also has better frequency response under the resonant frequency. At last, the curve of Seismometer frequency response is given.

This paper reports the development of a very compact and very-high sensitivity optical fibre hydrophone system using a distributed-feedback fibre laser with a cavity length of 10cm. A theoretical system design making use of a Mach-Zehnder interferometer, homodyne demodulation scheme and digital signal processing is described. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the distributed-feedback fibre laser sensor head. Results for noise spectrum below 100kHz are presented, as well as discussions on some key issues with designing such hydrophone systems. Although not the intention for the system, initial results also indicate the suitability of the DFBFL for intensity modulated sensing.

A portable conductivity meter controlled by singlechip computer was designed. The instrument uses conductance-frequency transformation method to measure the conductivity of solution. The circuitry is simple and reliable. Another feature of the instrument is that the temperature compensation is realised by changing counting time of the timing counter. The theoretical based and the usage of temperature compensation are narrated.

Recently, fiber-optic current sensor technology has reached a degree of maturity to compete with conventional instrument transformers. However, it has not been commercialized until quite recently because of a few instability issues, such as linear birefringence effect in the fiber-optic sensor coil and intensity noises caused by optical light sources and components. In this paper, we report on research efforts we performed to address these issues. Firstly we used different optical sources, such as an ASE source, a F-P multimode LD, and a DFB singlemode LD, to compare the effects by the light sources. Also we used different optical fibers, such as flint glass fiber, with different reflection mirrors. From the experimental results, we obtained output variation down to 1% in the presence of mechanical disturbances and the broadband source showed the best noise characteristics about 13~23 dB better than LDs. The details of the experiments with other design parameters are also presented.

Optical fiber current sensors have certain privileges that the traditional sensors couldn't support. However, when the fiber is deployed, a large degree of linear birefringence is induced in the fiber. This induced birefringence significantly reduces the sensitivity of the system and quenches the weak Faraday effect signal. We demonstrate that twisted the single mode fiber before it is annealed can largely eliminates the residual linear birefringence. It dramatically improves the possibility to employ the twisted single mode fiber that intrinsically had large residual linear birefringence for constructing an optical twisted electric current sensor. We design a new electric current sensor employing the twisted single mode optical fiber. This sensing system has been verified with good performance. The minimum detectable current was measured to be 1 A and the maximum measurable current up to 2kA with linearity lower than 0.1%, and dynamic range approaches 40 dB. Because of the advantages of high sensitivity, considerable wide dynamic range, and free from electric shock, this novel optic electric current sensor may open a new era in the applications of the electric power system.

A nanometer range displacement measurement system is presented where a reciprocal interferometer is employed whose configuration is similar to Michelson interferometer. Although the reciprocal interferometer is very simple and insensitive to environmental perturbations, we concluded that the spectrum analysis techniques could also be used to process the interference fringes and increase the measurement precision of reciprocal interferometry. Fast-Fourier transform and filter are used to eliminate the noises in fringes. The reconstructed fringes are very clear, which location can be measured accurately. Theoretical analysis is presented. Experimentally, the displacement of a nanopositioner-driven target was measured by using a reciprocal interferometer, a CCD camera, picture card and computer. The system has demonstrated a minimum resolution is 1.5 nm when the number of sample point is 512.

The dispersion properties of the reflection-induced retardance of the polarization-preserving reflecting medium layer and its effect upon the sensitivity of an optical current sensor are theoretically analyzed taking the Jones' Matrix as a mathematical tool and simulated with a computer. The investigation results show that the dispersion will obviously affect the scale factor of the system. Therefore, it is necessary to stabilize the driving current and the ambient temperature of the optical source by some technical means. These results might be useful for the researchers and designers working in the optical current sensing techniques area.

The finite element method was used to analyze the interior stress distributions and the birefringence of the side hole fiber. The paper has analyzed the dependence of the birefringence of the side hole fiber on the side holes' physical dimensions. The calculation result shows that the fast axis of the fiber is along the line which links the two holes' centers, the geometrical birefringence can be neglected, and the birefringence can be improved through increasing the radius of the side holes or reducing the distance between the core and the side hole centers.

At present, many floater-type measurement equipments whose readings are recorded by manpower are still in use in petrol-chemical industries. With regard to their low efficiency, great errors and their improbability in realization in automation management and remote control, in this instance, a new liquid-level meter system using the advanced fiber-optic sensing technology based on the floater-type level meter is developed. In principle, it measures the liquid level of the oil tank by using the principle of force balance, captures and transmits the light signals by means of the fiber-optic sensing technology, adjusts the light signals from continuous impulse signals to the discontinuous by the light-code disc, then converts light impulses into voltage impulses by photoelectric elements. In configuration, it adopts a twin light source and a twin optical-channel, utilizes twin fiber detectors to record the size of the liquid level and judge the direction of the liquid level respectively. Moreover, the measuring system has been tested practically in a chemical plant, the results indicate that the measuring errors are Less than or equal to ±6mm, relative errors are <2% when its measuring range is within 0 and 1000mm.It is proved that the various indexes of the system satisfies the demand of the industries and the capability is credible.

Based on the temperature dependence of the intensity of Brillouin scattering in optical fiber, a distributed optical fiber temperature sensing experimental system with Brillouin OTDR configuration was presented. In this system, a narrow line width LD was used as a light source. The output of LD was modulated into light pulses by an AOM. After amplified by an EDFA the light pulses were coupled into the test fiber to generate backscattering signal. A double-pass Mach-Zehnder interferometer was used to separate the spontaneous Brillouin scattering from the Rayleigh scattering. The temperature sensing experiments were carried out on two different length of fibers which were 4.25 km and 22 km long, respectively. The intensity changes in the Brillouin scattering signals due to temperature variation on both of the fibers were measured.

In this paper, acoustic emission wave vibration acceleration measurement system is presented. In the system the distributed Fiber Bragg grating(FBG) measuring probe is used. In order to fulfill wavefront filtering, space and frequency domain filering, frequency modulation continuous wave (FMCW), wave division multiply (WDM) and time division multiply (TDM) techniques are adopted, and optical wavelet filter is designed. Thus influences of transverse sensitivity, temperature noise and intrinsic noise of fiber can be eliminated automatically, and disturbance of imbalance and nonlinear optical signal can also be restricted efficiently. The system realize distributed measurement of the acoustic emission wave vibration acceleration. The range of measured acceleration is 4.3m/s²~340m/s², the range of frequency response is quasi-static~1000, the resolution is 7.5x10^-7nm/√Hz. The presented measured system is virtually significant theoretically and practically in some fields such as micro-vibration measurement and fault diagnosis of marine platform, large-scale building, concrete dam and satellite launch pad, etc.

The optic-fiber sensor for measuring steam quality has been made out based on the principle of refractivity modulation. It is made up of optic head, conduct optic fiber, light source, detector and electric circuits. Reflectivity on the boundary between optic head and two-phase steam flow can be determined by refractivity of both sides of the boundary. Intensity of reflected light on the boundary is related to the ratio of water and steam. Provided we know the value of temperature or pressure of the two-phase flow, densities of water and vapor can be known and steam quality can be converted from the volume ratio of water and steam. The measuring range of steam quality is 0-100%, and the accuracy is decided by the level of steam quality measured and by resolution power of the sensor. The resolution and sensitivity of the sensor can be tested with two sorts of liquid of known refractive index. Meanwhile, the stability of output of the sensor is also approved. The sensor has been successfully used in measurement of steam quality in a steam-injection oil well with temperature of 270°C and pressure of 8MPa. The measuring result of steam quality tallies with the actual situation.

A technique for temperature compensation in fiber grating vibration sensor is reported. By special design, it causes reversed strain on two FBGs and has temperature effects cancelled. After discussion about the factors affecting the sensitivity and the width of frequency band, it is experimentally proved that the total variation in wavelength difference within temperature of -15 ~ 50&deg;C is nearly 0. When the input vibration frequency is up to 800Hz and the drive power is as low as 2mw, the output waveform is still distortionless.

A novel wavelength detection and demodulation technique of fiber Bragg gratings sensors is put forward. The principle, experimental setup and results of the sensor are analyzed. The new technique converts detections of shift of center reflecting wavelength into detection of light intensity extremum. Furthermore, a spatial division multiplexing system of Bragg gratings sensors based on the novel technique is developed. The multiplexing numbers are not confined by bandwidth of light source and tunable scope of single fiber Bragg grating.

This paper introduces one on-line measuring system of the metal surface roughness. The system is based on the theory about light's diffusing of the metal surface. Laser is used as the lamp-house of measure and in the system detector collects the light's signals by optical fiber. The surface roughness measuring principle and method are presented and the experiment data are analyzed. After comparing with other approaches, the standard-sample-plate comparison is adopted. The method is simple in structure and high in efficiency and the one-by-one measuring points can reflect the real surface. As for all the factors can induce errors in on-line measuring, the research obtains good result by revising the errors with reparative formula.

A novel tilt measurement method is proposed based on self-demodulated fiber Bragg grating (FBG) sensor system, which consists of a couple of matched FBGs and a cantilever-based pendulum clinometer. With a cantilever structure, the tilt angle is measured by means of a differential form of Bragg wavelength shifting, with which the cross-sensitivity of temperature is eliminated simultaneously. It has been proved by both simulations and preliminary experimental results that a high resolution better than 0.0022 degree can be achieved in the range of +/-10 degrees.

Based on the optical beam deflection (OBD) technique, a fiber-optic diagnostic technique is applied to investigate the pulsation of a laser-induced cavitation bubble on the vicinity of an aluminum target in water. The sequence waveforms induced by the bubble pulsation is presented and analyzed in detail. The maximum radii corresponding to each pulsation are determined. Furthermore, by varying the acting laser energy, the variation of the maximum bubble radius and bubble energy with respect to acting laser energy is obtained. The theoretical and experimental results are in good agreement within a relative error.

An intensity modulated optical fiber accelerometer is designed. It can be applied in the real-time measurement of dynamic vibration acceleration. The theoretical analysis shows that the relation between the light intensity and displacement can be indicated by the same expression just with the difference in coefficient, though models of the fiber-optic intensity distribution at launching fiber end are different, such as Gaussian distribution, uniform distribution and those midst the upper two. Because of the simpleness of the expression, by means of specific linearization processing for the modulating function, a real-time and undistorted acceleration signal can be obtained. A particular compensation is adopted to avoid the effect due to the static drift of the original distance between the launching fiber end and the reflective surface.

A temperature sensor based on polarization non-reciprocity in fiber Sagnac interferometer was proposed and investigated theoretically and experimentally. Special signal detection schemes were proposed and an experimental system with an all polarization configuration was setup. The temperature measurement experiment was done within -40°C ~ +60 °C range and the stability were investigated at absolute 0 °C in mixture of ice and water respectively. The result agrees with theory well and good performance has been obtained with parameters optimized. Discussion shows that this kind of temperature sensor can achieve high precision and has great application potential.

An optical fiber temperature sensor based on optical fiber coupler and evanescent wave is presented. The overall goal of our research is to design a temperature sensor system which is used to monitor temperature accurately. Coupler is used as the sensor probe. Such kind of coupler uses standard communication SM fiber to be a sensing component of evanescent wave. The probe is obtained by replacing the cladding of coupler region with temperature sensitive material. The whole system is then exposed in a thermal bath. A numerical modeling of the sensor based on supermode theory is studied and the result is simulated. At last, the system for temperature measurement in experiment is simply described.

A kind of fiber optical temperature variety sensor based on fiber optical ring resonator is presented. The temperature variety causes the variety of the round-trip phase of the ring and the movement of the resonance dips. The magnitude and rate of the movement are proportional to the magnitude and rate of temperature variety, respectively. Through the measurement of the dips movement, the temperature variety can be sensed. In this paper, we make a theoretic analysis about the sensor, propose the system configuration, present a simple and effective signal detection method, and analyze the performance of the sensor. This kind of temperature sensor has such characteristics as high sensitivity, simple detection method, flexibly changeable sensitivity for different applications and temperature variety detection. Combined with the multiplex technology such as time division multiplexing (TDM), the sensor can form temperature variety sensor array for distributed fiber optic temperature detection.

Photonic Crystal Fibers (PCFs) have recently attracted many attentions from research groups worldwide and many novel applications have been developed. We find that this kind of special fiber also enables various new possibilities for the construction of novel optical sensors that are highly compact and functional. In this paper, a novel stress and strain sensor based on triple-core PCF is proposed. The triple identical solid cores are triangularly arranged to detect the stress from different transverse directions as well as the strain in the longitudinal direction. Fiber cross-section structure variation due to stress is simulated in a PCF structure. Different mode distributions caused from stress in the triple-core structure is systematically investigated for the first time to the best of our knowledge. Meanwhile, output mode distribution sensitively changes with fiber length variation caused by strain. Relationship between sensitivity and fiber geometrical structure (fiber length, hole diameter, hole to hole center pitch distance) are explored and analyzed. We conclude that the PCF-based stress sensor exhibits many functionality and advantages such as totally single-mode operation, short length, strong sensitivity of strain, and good sensitivity of stress from all directions in the fiber cross-section. Furthermore, three identical endlessly single mode PCFs will be fused together and tapered to construct a triple-core structure. Various parameters are measured and tested upon this tapered trip-core PCF and the results will be published soon.

A reliable distributed temperature monitoring is very important for electric power systems because a power system failure will result in an enormous loss of life and property. Fiber Bragg grating (FBG) sensors, which have been studied intensively for last decade, can be very efficient tools for these applications because they are immune to EMI and can be highly multiplexed, which enables efficient quasi-distributed temperature sensing along tens of km range. We constructed a FBG sensor array system for temperature monitoring of power cables. For reliable sensor implementation, the FBG array is embedded in a metal tube which protects sensors from external disturbances and enables easy installment by soldering. The temperature-induced Bragg wavelength variations are accurately monitored by a scanned tunable wavelength filter. Differential measurement with a temperature stabilized reference grating and a curve fitting algorithm has been used to enhance measurement accuracy in temperature range of 25°C~70°C.

We propose an efficient phase stabilization/shifting technique for the use in fiber-optic ESPI system by using a Fuzzy PID controller. To obtain required phase steps between the CCD captured speckle patterns, we implemented a Fuzzy-logic-based PID controller which is known as more suitable for nonlinear, time-delayed, and vague systems. Phase steps with a quarter-wave phase difference, which are required for four phase step methods, are continuously generated by a closed-loop switching and a synchronization signal. From the experimental results, the Fuzzy controller system has shown the faster and more accurate phase stabilization and continuously generated the four phase shifting in the presence of ambient temperature drift and vibration.

A novel bidirectional center wavelength tuning method of Fiber Bragg Grating (FBG) was put forward in this paper. It is based on bidirectional temperature control unit, including semiconductor cooler/heater, negative temperature coefficient (NTC) resistor and peripheral circuits. The cooler/heater, NTC and a FBG were integrated in a DIL metal package like common laserdiodes. Wavelength tuning experiments were carried out at three different environment temperature (0°C, 20°C and 40°C), and the temperature tuning range is from -20°C to 60°C with a step of 10°C. The experimental results show that center wavelength of FBG changes linearly along with temperature variation, and the linearity is better than 0.9986, moreover, environment temperature has little influence on FBG's center wavelength.

We propose the use of optical fiber Bragg gratings in a non-invasive blood pressure waveform monitor. Bragg gratings can be written in a Fabry-Perot interferometric configuration to yield a method of strain measurement that has both a high resolution and a wide unambiguous range. This fiber Bragg grating Fabry-Perot interferometer (FBGI) can be used as a sensor to detect strain resulting from blood pressure applied to the walls of an artery situated near the patient’s skin. Strain measurements taken on the skin surface, typically over the radial artery at the wrist, are encoded as phase shifts of the FBGI signal. These phase shifts may be obtained by the analytic representation of the interferometer signal in the wavelength domain or by Fourier analysis in the frequency domain. For the proof of concept a realistic physical model was constructed to simulate pressure conditions at the actual sensor location. The operation of the device is demonstrated by measurements of pressure-pulse waveforms obtained in real-time. This sensor was also successfully tested on human patients, and these results are also presented. Since it yields continuous readings of blood pressure non-invasively, further application of the optical manometer may yield an alternative to conventional sphygmomanometry.

A Method to realize signal demodulation of fiber Bragg grating (FBG) sensing system using non-balanced fiber Mach-Zehnder interferometer based on phase generated carrier (PGC) technique is proposed. A detecting scheme to realize phase carrier modulation using PZT phase modulator and to realize demodulation of detected signal using Bessel function and Fourier analysis is presented. The results of the analysis show that the upper limitation of the dynamic range in fiber Mach-Zehnder interferometer is limited by the frequency of the carrier and the cut-off frequency of the low pass filter. In order to enhance the function of filtering wave in phase generated carrier signal demodulation, we use digital matched filter (DMF) in place of low pass filter. The filter can be used to recover the useful signals from signals of a low signal-to-noise ratio. The wavelength detection accuracy of this demodulation scheme is 1.8pm, and the dynamic range of the FBG sensing system has been also improved. The theoretical analysis shows that the scheme can effectively suppress effect of random interference signals on the measurement accuracy and can demodulate the dynamic signal with high resolution.

North-finder system is an important application of the inertial technology. It provides true north azimuth information to all kinds of ground-based equipment. This paper designed a dynamic automatic north-finder based on the modulation output of fiber optic gyroscope (FOG). In this scheme, the sine output signal of the FOG was sampled and disposed, and then the real north of surveyed point on the surface of earth was calculated. The deviation caused by the base tilt was compensated by an accelerator. The output signals of FOG and accelerator were computed combined with the position sampled from increasing encoder by digital signal processor. Successive rotating technique was adopted to modulate the FOG signal periodically. Most of the low frequency part of random gyro drift errors was compensated. The north-finder accuracy was improved compared with the traditional static measuring method. The test result shows the FOG automatic north-finder obtains 2'true north angle accuracies within not more than three minutes, can meet the orientation need of artillery, terrain measurement vehicle, armored car, unmanned drive vehicle, geodetic survey and tunnel exploration.

Methane is the main composition of natural gas and marsh gas. It is an important industrial raw material and combustion gas in daily life. Detecting methane and its concentration in time has utmost important affect on safe operation of industry mine and person safe. Developing methane-detecting system has become an important topic and research direction of gas detecting domain. Through processing weak signal with harmonic detection technique, a multi-point fiber-optic gas sensor system for measuring the concentration of methane is designed based on light absorbing capability of gas, which varies with gas concentration at its characteristic wavelength. DFBLD (Distributed Feedback Laser Diode) in 1300nm waveband is used as illuminant and phase-detecting technology is used to carry out harmonic wave detecting the concentration of methane. Study shows that the accuracy of instrument is 5ppm, accuracy and stability of the sensor can meet practical demands. It can be applied to multi-point measurement at real-time in multiple occasions.

Three metallized methods for forming a film on fiber core to monistor corrosion process have been studied and compared. The first one is sputtering nickel controlled by magnetic field under vaccum environment. The second and third is respectively chemically electroplating silver and physical vacuum depositing (PVD) iron. The former two methods aim at forming middle layer for conductive electricity to provide conditions for further electroplating steel. The comparative aspects include electrochemical measurements, such as Cl- affecting on open circuit potential Ecorr and linear polarized resistance Rp. Furtherly, a metallized fiber is prepared to monitor corrosion of ship hull steel, which is approved by scanning electronic microscope and X-ray diffraction analysis. The shifting of output light power displays corrosive process of steel.

We report our research on the development of optical fiber trace gas sensors for environmental applications. A novel optical fiber sensor for monitoring acetylene (C2H2) gases is described. Through studying the measure theory, we use the Beer-Lambert law to monitor the gas. And after analyzing the C2H2 spectrum, we select Distributed Feedback Laser Diode (DFB LD) as light source. Comparing many kinds’ sensor detection head, the gas absorbing cell with tail fiber can have good coupling with optical fiber and improve the coupling stability. In the data processing system, signals are distilled by lock-in amplifiers and then harmonic measure technology processes that distilled faint signals. After the all, the electronic signals are transmitted into computer to process, alarm and display. We design the instrument who can remote and on-line measuring acetylene. Through theory analysis and system experiment, the design of the system is practicable, and has a better precision and some apply foreground.

A study on Chemical Oxygen Demand (COD) measuring method is reported, in which the COD value is measured by an integrated liquid drop monitor sensor without any reagent and chemical treatment. The integrated drop sensor consists of a liquid head, an integrated fiber sensor and a capacitor sensor. The capacitor sensor is composed of a drop head and a ring electrode. As the part of the drop head, the outline of the drop will be changed during the drop forming, which result in the variation of the capacitance. The fiber sensor is composed of two fibers that are positioned into the liquid drop. The light signal goes into the liquid drop from one fiber and out from the other one. A unique fingerprint of the liquid drop can be got by the data processing. The matching between the COD value of a liquid and the codes of the fingerprints in the database are presented and discussed.

High temperature affects the photosynthetic functions of plants by its effects on the rate of chemical reactions and on structural organization. Delayed fluorescence originated from the reaction center of photosystem II (PSII) during the photosynthesis process shortly after stopped illumination. With lamina of soybean as a testing model, the effects of high temperature stress on plant photosynthesis capability were studied with various spectral analysis methods. Experimental results show that DF spectrum and Excitation spectrum can probably characterize the changes of soybean photosynthesis capability after different high temperature treatments. Meanwhile, the injury and harm degree of heat stress on soybean leaves were further studied by the variability of its chloroplast absorption spectrum. DF spectroscopy method may provide a new approach for fast detection of the effects of environment stresses on plant photosynthesis capability.

Oxidative stress is mainly mediated by reactive oxygen species (ROS). Evaluation of oxidative stress is helpful for choosing an appropriate method to protect the organism from the oxidative damage. In this study, a highly sensitive and simple chemiluminescence method is presented for the evaluation of radiation-induced oxidative stress in human peripheral lymphocytes. The lymphocytes were irradiated by ultraviolet radiation (320-400nm, UVA) with different doses. The ROS generated by the lymphocytes was detected by chemiluminescence method, using a highly sensitive chemiluminescence probe 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-α] pyrazin-3-one (MCLA). The cell viability was detected with Cell Counting Kit-8 (CCK-8). The malondialdehyde (MDA), a marker of lipid peroxidation and oxidative stress, and the total antioxidant capacity (TAC), a parameter that is taken as evidence of oxidative stress, were measured too. The results show that both chemiluminescence intensity, cell mortality and MDA concentration of lymphocytes grow with the increase of UVA dose range from 0.5 to 8 J/cm², while the TAC decreases. There exists a positive relationship between cell oxidative damage degree and the chemiluminescence intensity of lymphocytes. This highly sensitive chemiluminescence method would potentially provide an easy way to evaluate the level of UVA-induced oxidative stress readily, sensitively and rapidly

Air pollution monitoring is an important aspect of environmental protection. The pollutants to be detected are usually more than one in air or smoke monitoring. Researching new techniques that can meet the demand of detecting the pollutants at the same time is important and necessary. The paper researched the method of detecting multi-parameters in one optical fiber gas sensing system. The system used multi-wavelength and time division multiplex technique to detect the concentration of SO₂ and NO₂ simultaneously based on gas' spectra absorption principle. The light differential absorption formula was deduced. The two strong and weak absorbing wavelengths were chosen as signal and reference relatively. To every gas, optical coupler and narrow-band optical filters were used to generate signal and reference light from a high brightness LED. The central wavelength of filters is identical to the strong or weak absorption wavelength respectively. The multi-channel signals were switched to one light beam using a 4x1 optical switch controlled by computer in designed time sequence. The output light after absorbing by gas was coupled on a high sensitivity PIN detector. To achieve high detecting sensitivity, the light source was modulated by a pulse signal. The power and temperature control circuits were also used to stabilize the output power and wavelength of light source. After differential absorption process, the concentration of different gas can be deduced in one set of common optical and electrical sensing system.

WO₃ thin films have been widely studied because they exhibit the electrochemistry effect i.e. a reversible change of color when in contact with an electrolyte and under bias or light illumination which can be used in smart windows and displays. In this work, the optical properties of tungsten oxide films prepared by DC reactive magnetron sputtering and sol-gel method were investigated. The transmittance of the samples was investigated by double-beam UV-VIS-NIR spectrophotometer respectively. The transmittance of the samples changed greatly with wavelength in the range from 250nm to 350nm and was a minimum at about 280nm. The transmittance of samples prepared by sol-gel is better than that by DC reactive magnetron. Molecular structure and surface morphology of samples were obtained by AFM. Film materials prepared by DC reactive magnetron sputtering method are evener and compacter than those by sol-gel method. The molecular of sample by sol-gel is obvious tetrahedron and the molecular of sample by DC reactive magnetron tends to be planar constructure. The chemical bonds of W-O and O-O of the samples are about 0.5nm and 0.6nm long respectively.

The article mainly focused on mobile on-line air quality monitoring system. By deeply analyzed DOAS theory, we designed this new air quality monitoring system. It is mobile and may monitoring many pollution sources on-line everyday. The Differential Optical Absorption Spectroscopy (DOAS), based on the work by U. Platt and co-workers, is becoming increasingly popular for environment monitoring. DOAS may measure many trace gases like NO₂, O₃, BrO, NO₃ , and SO₂. It is designed for the measurement of primary and secondary urban air pollutants with high precision and little cross interference. In the DOAS technique, the spectrum of an artificial light source within a given bandwidth is measured after passing through the open atmosphere for between 100 m and 10 km. After removing the emission spectrum of the light source, the remaining differential absorption features are compared with the absorption cross sections of relevant trace gases. This allows both the qualitative and quantitative determination of their concentration in the light path. After deeply research, we design this new system. It uses fiber spectroscopy, and it is mobile. User may monitor many pollution sources in a car. This makes auto-monitoring more easily. Our DOAS system has these merits: New Light Emission-Receiver Unit which united emission,receiver and collimation lenses. New Background Elimination Fiber. And dynamic-feedback self-adapting program. In our experiment by this design idea, we get accurate data.

Using highly pure water disposed by Milli-Qlabo purifying system of United States as background water, employing RF540 fluorescence spectrometer and selecting fourteen wavelengths as excitation wavelengths, this paper measured and analyzed excitation spectra and fluorescence spectra of oil-water intermixtures with different concentrations from eight domestic mineral crude oils, seven imported mineral crude oils and eight mineral product oils. Experiment results show that: all of these oils can emit fluorescence in broad range of excitation spectra, but the fluorescence quantum efficiency is different; optimal excitation wavelength is 254nm, while more effective excitation wavelength is 360nm, and the corresponding optimal fluorescence detection wavelengths are 360nm and 460nm; with the increment of concentration, relative intensities of fluorescence also increase linearly, which shows that they have obvious positive correlation and the correlation coefficient is above 0.9. Thus using fluorescence method to directly measure the content of mineral crude oil and product oil in water is feasible. Based on the experimental work, combining transfer characteristic of optical fiber, the ranges of optimal excitation wavelength and detection wavelength of mineral oil in water are confirmed, which founds for the on-line fluorescence measurement with optical fiber of micro-content of mineral oil in water.

Because laser is scattered and attenuated acutely by the water, diffuse reflection of Gauss laser pulse comes back with discrete single photon. These discrete single photon can not form a complete echo wave corresponding to original laser wave. The detector can only output discrete pulses with probability of η(quantum efficiency) . The discrete pulses caused by echo wave, background light, electron hot emission of detection do not have distinct different characteristics in time domain or frequency domain, so echo wave can not be distinguished from these discrete pulses by traditional detection method. Through analysing the signal and noise statistic characteristics., we put forward a method that apply known probability model to detect probabilistic echo signal to resolve the problem hereinbefore mentioned images. The signal is very low in underwater laser ranging, so it is very difficult to recognize the echo wave. This paper introduces n method and uses it to process the signal. digital threshold detection is simulated with laser ranging radar and we get good results. This study will help to greatly improve the ability of laser ranging radar.

Fiber optical systems are becoming increasingly important for measurement of current and voltage in high voltage environments. Conventional electrical wiring such as transmission line for voltage transformers can readily be replaced by noise-free fiber optics. A novel active voltage transformer with an optical data communication link has been demonstrated. The system includes a transducer based on the capacitive divider and two electrically isolated signal conditioning sections with optical fiber communication link. The proposed solution allowed for designing and developing a novel and high-performance voltage transformer for in-field application. A prototype version of the transformer was constructed following the new standard, with digital output interface to protection devices and the experiment results confirmed a 0.2 accuracy class.

In this investigation, an interferometric scheme is developed to determine the linear birefringent parameters of wave plate in full range. A commercially available Soliel Babinet compensator and a half wave plate are taken as sample to demonstrate the capability of two-dimensional measurement. Since images are obtained with respect to different polarization orientations of a linearly polarized incident laser beam, the measurement speed can be improved once the polarization orientation adjustment is achieved electronically. The measurement is also independent of non-uniform distribution of laser intensity, this is demonstrated experimentally and briefly explained theoretically. In addition, the 2-D distribution of residual linear birefringent parameters is also demonstrated.

The light-emitting properties based on ladder-type poly (P-Phenylene) (LPPP) with carbon nanotubes were investigated. The light-emitting devices with the heterostructure are consisted of the hole transporter LPPP and the electron transporter Alq3. Carbon nanotubes of 1 wt % were added in LPPP. The microcavity effect could be achieved by adjusting organic layers between Au and Al electrodes. It was also found that the light emission intensity was further increased and the emission peak was narrowed after doping carbon nanotubes as compared with that of samples without carbon nanotubes. This may be ascribed to increasing conductivity and mobility of organic lagers via doping carbon nanotubes.

A method to measure displacements based on Moire technique and polarization modulation is presented and analyzed with Fourier transform and Jones matrix in this paper. A collimated laser beam illuminates a scale grating moved in the direction perpendicular to its groove. The scale grating is imaged on a two-phase index grating through a 4f system with an aperture in its frequency plane to form Moire fringes. The scale grating and the index grating have same grating period and their line and space ratio is 1:1. Two sections of the index grating are imaged on two parts of a bi-cell detector through a telecentric system, thereby the displacement of the scale grating can be obtained by detecting the Miore signals on the detector. Before the index grating, a polarizer and a Savart plate are placed. In the telecentric system, a photoelastic modulator between two quarter-wave plates and an analyzer are arranged. Thus the polarization modulation of the Moire signals is realized. The polarization modulation improves the measurement accuracy of the displacement. The analysis shows the displacement measuring method is of nanometer accuracy. In experiments, we verified the feasibility of the method. The repeatability of the method was less than 12nm.

A new laser ultrasonic sensor for testing samples' thickness is developed. This sensor has high-frequency response and high sensitivity. Furthermore it is easy to adjust. When the sensor is used to focus on polished iron plate, well-defined longitude-wave and its echo waves can be obtained. Based on the experimental results, the sample’s thickness can be deduced. The theoretical and experimental results are in good agreement with relative error of 0.5%.

A new method based on the principle of broadband-light interference, which combines reflected spectrum analysis and optical fiber techniques, is proposed to measure surface profile of opaque film. The testing system mainly consists of a Michelson interferometer. Incident light is split into a reference beam and an input beam to the sample. When two lights reflected from the surface of film and mirror may interfere within the range of broadband light coherent length, the output of interference patterns is measured by a spectrograph. The optical path difference of the sample point and the reference mirror is tested by analyzing the interference pattern. When the reference mirror is fixed, the relative thickness value of different measuring points on the film's surface is achieved by scanning the film's surface. Its testing range is from 0.2 micron to less than 20 micron. According to the relative thickness data, the film’s surface profile is obtained. The result shows that the testing error of this method is within 2 nm. This method has the advantages over the other measuring method, such as nondestructive, higher accuracy and simple structure.

Non-gyro inertial measurement unit (NGIMU) uses only accelerometers replacing gyroscopes to compute the motion of a moving body. Use the traditional accelerometer configurations for reference, a novel nine-accelerometer configuration of NGIMU is proposed with its mathematic model constructed. This configuration can acquire the expressions of the angular accelerations directly and avoid calculating the differential poly-equation. To confirm the effectiveness of the design, the experiment system is set up and the DSP data processing circuit is also done. In addition, the experiments of the angle estimating are performed and the results show that the design can reflect the trend of the angle changing with high precision to some extend.

In this paper, we demonstrate the evolution of the self-mixing phenomena of dual-polarization microchip Nd:YAG lasers as we change the feedback strength and the frequency difference. At high feedback level the microchip laser's polarization flips orthogonally as the external mirror moves. Especially, we observed that the intensity modulation amplitude varies periodically with the frequency difference of orthogonal polarizations, and that with different types of targets the periodic change always exists. A qualitative model is put forward and is in good agreement with the experimental results. The results can be applied to the self-mixing sensitivity enhancement, and also presents a novel method of absolute distance measurement.

Video tracking is necessary for measuring the deformation of flying insects' wings and investigating their motion patterns. However the tracking speed is limited by the frame frequency of the camera for a conventional video tracking system. And for a system based on high-speed camera, it is difficult to process the images in real time. Here we proposed an optical and magnetic hybrid tracking system. In this system, search coil sensors are utilized to detect the magnetic field on the position of the target within a cubic space, where the magnetic fields distributed. Then a computer and signal processing circuits are used to determine the coordinates. As a result, the target's images can be captured by a video tracking system including a high-speed camera and a two-dimensional tracking mirror. The target can be a flying insect or other moving objects. When it carries the sensors and moves in the magnetic field, the system can track it and take pictures. In this paper we present the details of the hybrid tracking system and make a discussion on it.

This paper presents the development of an airborne pushboorm hyperspectral imager having a cross-track field of view of 42 degree and a 2×2 m ground sample distance (GSD) from a nominal 2 km flight altitude. In order to provide a wider field of view and higher spatial resolution to meet requirement for a typical earth observation mission, the field putting technique was applied in the development for the difficulty of design and fabrication of large field of view lens and large area array charged coupled device (CCD). The hyperspectral imager is composed of two imaging spectrometer which each has a cross-track field of view of 22 degree. The alignment accuracy of field putting is finer than 5% of instantaneous field of view; it will be maintained by optomechanical configuration after putting finally.

Metal bellows is one of important components for mechanical sealing. Because the seam is very thin, and its spatial position is strictly limited, it is very difficult to observe the welding seam in order to control the variables of welding in real-time, the welding quality can not usually be guaranteed under the traditional technology. A novel approach is proposed, which is able to provide an amplificatory and clear image of the micro-plasma welding seam observed from better perspective, then output the image to computer and process it so that the variables of welding can be controlled in real-time. A special optical sensor has been designed and realized according to the approach. The principle and main technologies of the sensor is described in detail. The results of applying the system in practice approved the approach is successful. The welding quality of the inner circle of metal bellows, as well as the working condition of welder has been improved after the system is applied.

A 3D measuring system on structure light which uses color-encoded technique and digital projection technique to realize 3D measuring is introduced. In this measuring system, a color-encoded pattern that is created by a new method is created by software on a computer and then projected to an object by a digital projection system controlled by the computer. The image of the object is captured by a CCD color digital camera position at an angle different from that of the digital projection system. The color of each pixel determined by the proportion of its primary color, red, green, and blue (RGB) has a one-to-one correspondence with the projection angle. Decoding and calculating for the color image captured, the 3D coordinates of the points on the object surface can be obtained.

The technology of multi-target tracking is always detecting small targets in complex background. According to the frequency characteristic of nature background and small target, a method of detecting targets based on wavelet energy is suggested. The energy of targets in horizontal and vertical direction outclass that of background, or we can say, the gray degree of targets outclass that of background. Then through selecting adaptive region-value, targets and background can be divided. By the method of classifying, the figure centers of every target can be calculated. According to the figure centers of every target in several neighboring frames, the position and velocity of every target in next frame can be estimated by Kalman filter. Experiment results have shown that small targets in sea or sky nature background can be detected by this method, and they can be tracking.

In the process of robot Welding, position of welding seam and welding pool shape is detected by CCD camera for quality control and seam tracking in real-time. It is difficult to always get a clear welding image in some welding methods, such as TIG welding. A novel idea that the exposal time of CCD camera is automatically controlled by arc voltage or arc luminance is proposed to get clear welding image. A set of special device and circuits are added to a common industrial CCD camera in order to flexibly control the CCD to start or close exposal by control of the internal clearing signal of the accumulated charge. Two special vision sensors according to the idea are developed. Their exposal grabbing can be triggered respectively by the arc voltage and the variety of the arc luminance. Two prototypes have been designed and manufactured. Experiments show that they can stably grab clear welding images at appointed moment, which is a basic for the feedback control of automatic welding.

There are two main image sensors that are now being widely used in image capture system: CCD and CMOS imager. The fill-factor of CMOS imager is lower than that of CCD, so it is of great importance to consider the influence of the fill-factor on sub-pixel measurement accuracy. the main purpose of this paper is to give a discussion of sub-pixel measurement accuracy of CMOS imager based on a digital camera which is designed and manufactured by ourselves. Conclusion is presented at the end of this paper, that the sub-pixel measurement accuracy of CMOS imager OV7620 can be 1/6 pixel.

According to image correlation and stereoscopic vision theory, an improved digital image correlation is proposed, which is called as three dimensional digital marker method. The stereoscopic vision and image correlation techniques are integrated, the symbol point before and after deformation is tracked and registered by image correlation algorithm, three dimensional displacement is restored by the two dimensional displacement component in image plane of both cameras. The new method is an improved version of previous two dimensional digital marker method, which not only has the advantages such as experimental procedure simpleness, wide range of deformation measurement, but also extends the applicable scope. Finally, the proposed method is used to the foam specimen rigid translation. The results show that the new method is capable of measuring three dimensional displacement simply and quickly.

This article discussed detailedly the framework and key technologies of omni-azimuth laser target identification and communication system. Including the whole technological scheme which can realize omni-bearing, The article describes the structure of electric control system (multi-machine system design, parallel processing and so on) and some key technologies about the Laser selection, signal processing and the character identification of an omni-bearing laser target identification system.

Ellipsometry is known as high precision metrology for thin film thickness measurements with sub-angstrom resolution. In ellipsometric measurements it does not measure film thickness or optical constants directly. It measures ellipsometric parameters, ψ and Δ, namely, defined as the ratio of reflection coefficients for p- and s-polarized light. Generally in rotating component ellipsometry, light intensity values at more than 256 angular positions of polarizer or analyzer with discrete Fourier transform methods are used to evaluate Fourier coefficients, which can be calculated to ellipsometric parameters explicitly. Using this scheme it is well suited in single point measuring ellipsometry, but it degrades measurement speed in imaging ellipsometry. In imaging ellipsometry due to the limitation in CCD detection speed, rotating components must move stepwisely, so more discrete positions of polarizer or analyzer takes more measurement time dramatically. So we propose four frame method which can be easily substituted for conventional discrete Fourier transform methods. Four frame method can save measurement time, but natively intensity measurements at only four angular positions can cause erroneous results in Fourier coefficients compared with that of discrete Fourier transform method. In the four frame method, many repetitive measurements for light intensity at each angular position can solve these shortcomings. That is, conceptually to reduce random noise in ellipsometric measurements, conventional discrete Fourier transform method uses spatial averaging technique, but four frame method uses temporal averaging technique. In our experiments we could get more than ten times fast measurements with four frame method.

The effects of the linear birefringence inside a bulk glass current sensing element and the incident polarizing angle upon the performance of a bulk glass optical current sensor are derived and analyzed theoretically. The investigation results show that the linear birefringence will modify the scale factor of the system with a sample function; it can also affect the extent of the influence of the incident polarizing angle, at the same time. When the incident polarizing angle has some special values such as 0, 45, or 90 degree, its effect to the system will be zero. These results might provide some useful reference to the researchers and designers of bulk glass optical current sensors.

The wavelength dependence of the sensitivity of a bulk-glass optical current transformer is theoretically analyzed taking the Jones’ Matrix as a mathematical tool, simulated with a computer and verified with an experiment. The results show that the wavelength dependence will cause obvious sensitivity fluctuation of the system because of the existing of the dispersions of the reflection-induced retardance, Verdet constant and the linear birefringence inside the bulk-glass current transducing head. Therefore, it is necessary to stabilize the driving current and the ambient temperature of the optical source used by some technical means, because these two factors can result in wavelength variation. These results might be useful for the researchers and designers working in the optical current transducing techniques area.