Photochromism and real-time holographic recording were characterized for two principal classes of photochromic compounds: spiropyrans and fulgides. For spiropyran molecules, important thickness and writing intensity effects were observed. Concerning fulgide, in PMMA matrix, the closed form presents a maximum of absorption centered at 525 nm upon irradiation at 365 nm. We have determined the photoreaction rate constants k_UV and k_vis respectively for the coloring and bleaching process: k_UV equals 1.2 X 10^-3 s^-1 and k_VIS equals 11.1 X 10^-3 s^-1. Photochemical fatigue resistance in different polymer matrices was investigated. We found a loss of 9, 11, 13 and 35 percent respectively in PS, CA, PMMA and PVK. Concerning holographic recording, we obtained diffraction efficiency (eta) equals 0.65 percent in PMMA films 30 micrometers thick.

The formation of dynamic holograms in iron doped lithium niobate is studied with eh 532 nm wavelength diode pumped solid state laser. It is observed that these holograms had higher diffraction efficiency in comparison with the holograms written with 488 nm. These holograms are then dynamically reconstructed with either the 532 nm or 633 nm. The choice of writing the holograms with the 532 nm and reconstructing with 633 nm leads to a whole lot of applications in real-time holographic interferometry and data storage is also discussed.

Dichromated polyacrylic acid (DCPAA) and dichromated polyvinylalcohol (DCPVA) have been investigated with a double approach: photochemical behavior and holographic results. The study focused on two particular systems: the effect of the addition of nitrilotriacetic acid (NTA) or dimethylformamide to the photosensitive material. From the photochemical mechanism it was possible to assess that the complexing ability of both compounds plays a major role in the optimization of the holographic properties of the material. On the contrary, the presence of an electron donor like NTA in DCPAA is less favorable. A close correlation seems to be present between the photochemical behavior and the results obtained in holography.

In both design and fabrication, diffractive optical elements (DOEs) are more flexible and powerful than traditional refractive/reflective optical elements, hence an optical system with one or more diffractive elements may provide better optical performance at lower cost with small, light and compact structure. However due to its inherent large spectral dispersion, a DOE is generally designed and fabricated for one specific wavelength or a narrow spectral bandwidth. In the case of a wide band light source, chromatic aberration and loss of diffraction efficiency will occur. In this paper, the chromatic dispersion of DOE is discussed, and four achromatic strategies, namely hybrid diffractive/refractive strategy, harmonic diffraction strategy, multi-material strategy, and bi-blazed strategy are introduced and analyzed respectively. A comparison has also been made among them to guide the application.

We discuss the application of narrowband holographic filters for aerosense technique including laser radars, communication devices, etc. It is well known that very thick volume holograms both transmission and reflective type being illuminated by light indicate very high angular and spectral selectivity. The variety of sensor require such selection. We report the experimental result of recording of selectors with nanometric bandwidth of spectral selectivity and milliradian bandwidth of angular selectivity recorded in photopolymer with diffusive amplification of about millimeter thickness. We investigated the affect caused by introduction of holographic filter into receiving signal: the influence of filter selectivity property on the spatial frequency distribution of light passed through the atmosphere. We analyzed the possibility to vary the shape of the output power spectral density by means of hologram apodization.

We report here a novel way to fabricate fiber LPG using moire pattern amplitude mask (MPAM). Theoretical analysis of diffraction effect on MPAM has revealed that geometric optics rules are followed when area concerned is so close to diffractive grating that even Fresnel approximation can not be used. Experimental result of grating written in As₂S₃ fiber support the theoretic conclusion. And the temperature dependence is reported also.

Two simple techniques for the compensation of the temperature effects in fiber Bragg grating (FBG) based magnetostrictive sensors are demonstrated, where two FBGs are arranged in such a way that the magnetostrictive effects on the two gratings are added together, while the temperature effects are cancelled out. The two FBGs can be bonded in perpendicular to each other onto the surface of a magnetostrictive plate, or onto the surface of two different magnetostrictive bars that possess close thermal expansion coefficients but magnetostrictive coefficients of opposite signs. In both cases, the Bragg wavelength difference between the two gratings is insensitive to the temperature and measures the sum of the magnetostrictive effects experienced by the two FBGs. Using these techniques, we have been able to reduce the temperature sensitivity of the sensor by more than 10 times.

The transmission characteristics of bent long-period fiber gratings (LPFGs) and their applications as sensors are studied experimentally. We demonstrate that, by bending a LPFG, two major rejection bands in the wavelength region of interest can be produced, whose relative strength can be controlled by the amount of bending. The wavelength separation between the two bands increases linearly with the lateral displacement of the bent LPFG and a linear tuning range over 40 nm is demonstrated. All these characteristics show no significant polarization dependence. We also find that, by mounting a bent LPFG on a proper material, the thermally induced bending effect can enhance or cancel the direct thermal effect. With this technique, we obtain temperature sensitivities of 0.01 nm/degrees C and -0.35 nm/degrees C, which are, respectively, about 1/5 and 7 times of that of a straight bare LPFG. A temperature-insensitive LPFG-based sensor for the measurement of the concentration of NaCl in water is demonstrated with a sensitivity of -0.35nm/molarity by keeping the temperature sensitivity at 0.01 nm/degrees C from 15 to 70 degrees C. By using the same technique, a strain sensitivity of -49nm/percent (epsilon) is obtained, which is about 15 times of that of a straight bare LPFG.

Biotechnology has recently been regarded as the technology of the 21st century. One important advancement of the biotechnology is the biochip technology which integrates the conventional biotechnology with semiconductor processing, micro-electro-mechanical, optoelectronic, and digital signal and image acquisition and processing technologies. In this paper, we give a brief introduction to the biochip technology in general, and describe the DNA micro-array technology as a specific example of this relatively new and burgeoning interdisciplinary research and development.

With this publication a precision blood-leak-detector is presented. The blood-leak-detector is used for recognition of fractures in the dialyzer of a kidney-machine. It has to detect safely a blood flow of ml/min to exclude any risk for the patient. A lot of systems exist for blood-leak-detection. All of them use the same principle. They detect the light absorption in the dialyze fluid. The actual used detectors are inferior to the new developed sensor in resolution and long-time stability. Regular test of the existing systems and high failure rates are responsible for the high maintenance.

Based on tissue microscopic fluorescence properties and optical parameters, a three-layer bronchus optical mode was developed to calculate the excitation light distribution in the tissue and the fluorescence escape function from the tissue by Monte Carlo simulations. The contributions of each layer in the tissue to total autofluorescence signal observed at the tissue surface were also estimated. In addition, the fluorescence spectrum of the bronchial tissue was also modeled using the obtained tissue micro- spectroscopic properties. It is found that the theoretically modeled spectrum agrees well with the in vitro tissue fluorescence in the spectral range below 520 nm or above 600 nm.

A new non-flowing laser light scattering method for counting and classifying blood cells is presented. A linear charge- coupled device with 1024 elements is used to detect the scattered light intensity distribution of the blood cells. A pinhole plate is combined with the CCD to compete the focusing of the measurement system. An isotropic sphere is used to simulate the blood cell. Mie theory is used to describe the scattering of blood cells. In order to inverse the size distribution of blood cells from their scattered light intensity distribution, Powell method combined with precision punishment method is used as a dependent model method for measurement red blood cells and blood plates. Non-negative constraint least square method combined with Powell method and precision punishment method is used as an independent model for measuring white blood cells. The size distributions of white blood cells and red blood cells, and the mean diameter of red blood cells are measured by this method. White blood cells can be divided into three classes: lymphocytes, middle-sized cells and neutrocytes according to their sizes. And the number of blood cells in unit volume can also be measured by the linear dependence of blood cells concentration on scattered light intensity.

Different types of fiber optic methane sensor, especially for ming application, have been reviewed in this paper. Optical absorption and differential optical absorption techniques for the remote detection of methane gas using low-loss silica fiber have been discussed. IR fiber optic, sol-gel and correlation spectroscopy methods have been described in brief. Another noble technique based on attenuation of evanescent field has been enunciated using D- fiber. Merits and demerits of each technique and its suitability to mining industry have been highlighted. Optical fiber, being a dielectric, non-metallic and non- sparking, is an intrinsically safe media and is ideally suited to the hazardous environment present in mines.

Immobilizing protein on glass surfaces is typically more difficult and less efficient than on plastic surfaces. Proteins are readily adsorbed on plastic surfaces in a single step. To simplify protein immobilization efficiency on glass surfaces and enhance its efficiency, styrylsilane and polystyrene were coated on glass to serve as protein binding substrates.

The use of visible radiation in medical diagnostic procedures, initially attempted some 60 years ago, has only very recently become feasible, due to advances in source and detector technology, and the availability of elaborate computer-based imaging processing algorithms.

A novel approach for the detection of nitrogen dioxide gas is described. This optical fiber based sensor (FOS) works on the principal of evanescent wave (EW) absorption phenomenon. EWs at the uncladded portion of a multimode fiber is utilized for the senor development by replacing this region with a coating of Metallophthalocyanine, which is thermally deposited at a reduced pressure. MPcs are very sensitive to NO₂ gas and there is a change in the EW absorption in the NO₂ environment. Compared to other gas sensing devices, this is highly sensitive technique. The attraction of this FOS is its simple architecture and the easiness to implement.

The optimum working wavelength of a fiber-optic sensor based on the surface plasmon resonance used in monitoring the water quality is studied theoretically and experimentally in this paper. This sensing system was composed of a broad- spectrum source, a fiber sensor head and a micro-optic spectrograph. The sensing fiber adopted was a silica/polymer multi-mode optic fiber, with the 400 um core diameter and 0.36 number aperture. The calculation results showed that there is an optimum working wavelength range corresponding to the given sensor head configuration. Through adjusting the structure parameters the sensing wavelength could be selected to drop into the wavelength range of the commercial semiconductor optical sources, which is beneficial to improving the practicality and the reliability of the sensing system. This system was used to test the impurity of the fresh water and a sensitivity of 8.9 X 10^-5, corresponding to 10 ppm, was reached.

This paper describes the result of the experimental investigation conducted to determine the percentage of water by volume in methanol. The suitability of a fiber optic Raman spectrometer for in-situ measurement of percentage of water by volume in methanol is demonstrated. The measured intensities at the characteristic Raman shift corresponding to Methanol are found to be inversely proportional to the volume of water present in Methanol. The results obtained in the form and average intensities in tabular form.

Recognizing, online, cops and weeds enables to reduce the use of chemicals in agriculture. First, a sensor and classifier is proposed to measure and classify, online, the plant reflectance. However, as plant reflectance varies with unknown field dependent plant stress factors, the classifier must be trained on each field separately in order to recognize crop and weeds accurately on that field. Collecting the samples manually requires user-knowledge and time and is therefore economically not feasible. The posed tree-based cluster algorithm enables to automatically collect and label the necessary set of training samples for crops that are planted in rows, thus eliminating every user- interaction and user-knowledge. The classifier, trained with the automatically collected and labeled training samples, is able to recognize crop and weeds with an accuracy of almost 94 percent. This result in acceptable weed hit rates and significant herbicide reductions. Spot-spraying on the weeds only becomes economically feasible.

In this paper, a portable sensing system is developed using fiber optic spectroscopy principle for measuring and detecting of stresses induced in plants due to nutrient deficiencies. Chlorophyll fluorescence in plants is used to monitor the effects of nutrient stress in plants. As this method aims at providing an early detection and warning of nutrient deficiencies, it gives an alternative to argument current semi-quantitative and destructive methods of nutrient analysis. Our early papers had demonstrated significant differences in the color reflectance of plants' leaves when plants were subjected to various nutrient- deficient media. Developed using off-the-shelf components, this digital sensing optical system could measure and detect the slight variation in the plants' reflectance and hence its chlorophyll levels. These relative levels of chlorophyll are determined by measuring the plants' color reflectance of light while using the wavelength of the healthy plants as a reference for comparison. This system comprises of a miniature spectrometer containing 1024 CCD detectors covering a visible light spectrum of wavelength ranging from approximately 400 nm to 800 nm and a reflective probe. A laptop with a PCMCIA A/D data acquisition card is used in conjunction with a customized program.

In this article, a kind of design philosophy of a integrated sensor system for 2D position is presented. The sensing unit of this system is a 2D CCD. Through increasing the signal- to-noise ratio of a constructed specific lightspot target and performing optical filter, and exported full video image signal of CCD which includes a group of isolated positive pulse caused by the target is formed. Through combinational logic and sequential logic processing to the full video signal, the target image's 2D position on the light CCD can be generated. Finally, the specific lightspot target's relatively 2D position in the visual field is gained. In addition, a typical application of the system in the computer information processing field are presented as well.

New generations of microelectronics and microsystem devices call for the utilization of a variety of new materials and the combination of materials with a widespread of their mechanical and thermal characteristics. Related thermo- mechanical reliability issues as well as functional aims bear a big challenge to understand and to design mechanical behavior of devices and components. Finite elements analysis of components and devices is widely utilized in the R and D process as a tool of predictive engineering. Unfortunately, uprising miniaturization, higher system complexity and advanced material application more often question mechanical modeling for simulation. So, a strong need exists to measure simultaneously stresses and strains on real components. At the IZM Berlin different classical kinds of laser methods have been used to determine deformation behavior of components due to thermo-mechanical load and functional performance of systems. The principal restriction of those methods with regard to spatial and measurement resolution had forced the development of new methods. In particular, microDAC a displacement and strain measurement method has been established. It bases on image processing algorithms permitting to extract strains form load state micrographs, which are picked up by SEM, optical microscopy and other high resolution imaging devices. Besides a brief review, corresponding interferometry and MicroMoire applications of the authors to micro deformation analysis, this paper mainly focuses on the microDAC technique. The basics of the microDAC concept, its main features like measurement resolution, data presentation and coupling to finite element analysis as well as applications are presented. Different kinds of measurements on modern electronics structures, like, e.g., used in flip chip technology, chip scale packaging and optoelectronics, illustrate its capability. Finally, a discussion of possible future developments is added, which can be directed to the adoption of higher resolution imaging equipment, namely scanning force microscopy.

After a short introduction on the theory and instrumentation of Raman spectroscopy, its application for local stress and temperature measurements in semiconductor devices is discussed. Examples are given for silicon isolation structures, transistors, solder bumps and back-grinding. It is shown how the resolution can be improved by using an oil immersion objective and deconvolution techniques. Different imaging modes are discussed and their resolution is compared. Examples of 1D and of 2D scans are shown.

An automatic method of full-field stress measurement using a transmitting micro-polariscope is proposed. A compact optical transmitting polarizing microscope with white light source is rebuilt by developing a loading and recording system, in order to perform a tension test. Both isoclinics and isochromatics are measured in real-time with phase shifting technique. A new simple algorithm for isochromatics is proposed. It is found to be suitable for the current micro-polariscope.

The grid method is combined with microscopy for micro deformation measurement. High density grids of 1200 lines/mm are transferred to electronic packaging specimens at high temperature. The residual stress distribution is recorded on the grid after it was cooled to room temperature. The grid pattern is magnified and digitally recorded with optical microscope, scanning electronic microscope, and atomic force microscope respectively. The recorded grid patterns are processed with Fourier transform technique. the spatial resolution degradation due to Fourier transform is discussed. It is found that the upper limit of spatial resolution for displacement measurement is half the grid pitch for grid method. Nevertheless the spatial resolution which can be attained is in micron to sub-micron region even with this degradation. A comparison on the effect of three microscopy techniques is also carried out.

A scanning laser doppler vibrometer employs Doppler frequency shift of a probe laser beam and interferometric mixing with a reference beam to measure target velocity. This technique offers high sensitivity, high spatial resolution and very low if any intrusivity.

Due to the importance of torsional vibrations in mechanical rotating structures, increasing interest is nowaday devoted to the development of experimental techniques for torsional modal analysis. The rotational laser Doppler vibrometer seems to offer large potentials in this field, as it allows the analysis of torsional vibrations also under operational conditions with simple and non-contacting set-up.

Optical Fiber Voltage Sensor (OVS) has potential applications in power supply network, but upon to now the OVS can not be industrially used in practice. This paper introduces some problems we met in development of practical bulk-modulation OVS using BGO crystal. The optical source must be pre-modulated so that to detected the average optical power easily. The measure error, nonlinear distortion, sensitivity produced by deviation of optical element are discussed. Analysis and test show, that a small collimating error of optical elements will lead to decrease the sensitivity and increase phase shift. So long as the angle (alpha) between the polarizer and (lambda) /4 wave plate is equal to (pi) /4, the location of the polarizer for detection and BGO is not very important and the maximum sensitivity can be achieved when the angle (gamma) between the detected polarizer and BGO is equal to (pi) /4. But if (alpha) does not equal (pi) /4 and (gamma) does not equal (pi) /4, not only the sensitivity will be decreased, but also the distortion will be increased, depending on the angle (beta) between BGO and (lambda) /4 wave plate. So we use a quartz plate to hold (lambda) /4 wave plate. So we use a quartz plate to hold (lambda) /4 wave plate in order to obtain good circular polarization light. In order to eliminate the effect of random fluctuation of average optical power, some data process must be needed. We use 80C196KC single chip CPU to calculate the instantaneous value, and the effective value of measured voltage can be displayed in this transducer. We use silicon gel insulator to introduce high voltage to sensor. Some calculation and test results are given in this paper.

This paper presents a novel bulk type of optical current transducer (OCT), in which a single-mode fiber to multi-mode fiber coupling configuration is adopt to reduce the optical loss and to restrain the random mode-coupling noise in a conventional multi-mode fiber to multi-mode fiber coupling structure. A special design is used to automatically compensate the changes of the State of Polarization (SOP) of the optical fiber. Experiment shows that about 10 times of precision improvement can be achieved compared with conventional sensing element without SOP compensation. The OCT system employs microcomputer together with corresponding software to accomplish signal processing. The OCT system employs microcomputer together with corresponding software to accomplish signal processing. The overall performance of the OCT system is tested experimentally. The results show that the system has good long-term stability - the precision during 100 hours is 0.3 percent, and temperature compensation can considerably improve the temperature characteristic of the system.

Optical current sensing has manifold advantages over the conventional device. It is of great benefit to develop optical current transducer. Due to the inherent birefringence of optical fiber, fiber-optic current transducer has lower sensitivity than bulk glass optical current transducer. Therefore, in research the bulk glass OCT is preferred to fiber optic current transducer. Because multimode optical fiber has larger core diameter and aperture diameter, the couple coefficient of light source to multimode optical fiber is much larger than that to the single mode optical fiber. So multimode optical fiber is adopted as the medium to carry the optical signal in bulk glass OCT. However, the polarization state of optical signal will change randomly because a multimode optical fiber is not polarization-maintaining. As a result, the intensity of the optical signal will change randomly. The sensitivity of the transducer will be suffered. And it makes the design of electrical equipment difficult. A way to solute this problem is discussed. And an inventive optical current configuration is described. Incident light is divided into two orthogonal polarized component through splitters. After a serial of processing, as dephasing etc, the intensity of output light can be proved to be independent on the polarization state of the incident light. Thus, the random variation of the intensity of the optical signa is eliminated theoretically.

The implementation of active processing strategies in optical 3D-inspection needs the availability of flexible hardware solutions. The system components illumination and sensor/detector are actively involved in the processing chain by a feedback loop that is controlled by the evaluation process. Therefore this article deals with new light sources and sensor which appeared recently on the market and can be applied successfully for the implementation of active processing principles. Some applications where such new components are used to implement an active measurement strategy are presented.

With this publication an automatic measurement equipment for quality control in the loop slitting department is presented. The sensor is a stand-alone system. A digital signal processor, a field programmable gate array, and a microcontroller collect and process the data of the linear CCD-sensors.

The use of a broad-band interferometer and its fringe analysis method are presented in which the fractional fringe order method for measuring the absolute thickness. An approximate integer part of the fringe order is estimated by mechanical measurements, and the fractional part is determined by interferometric fringe pattern analysis. The fringe patterns are obtained with a Michelson interferometer by illumination of several selected wavelengths, respectively. The use of the fractional fringe order method can determine accurately more than 2(pi) phase jumps. The influence of wavelength and approximate integer part of fringe order on the measurement accuracy is discussed.

In this paper we first survey non-contacting and separate measurement of thickness and refractive index of a transparent plate or film. Then we describe the separate measurement of refractive index and geometrical index and geometrical thickness of multiple layers which uses a combination of confocal microscopy and low-coherence interferometry. The measurement has been accelerated by replacing the low-coherence interferometry by wavelength- scanning heterodyne interferometry using a laser diode. Finally, accuracy of the measurement has been experimentally studied and display of a cross-sectional image of a stack of glass plates has been demonstrated.

In this paper, a novel beam shaping configuration for confocal imaging system is presented, which relies on the reversal effect of axicons-component along with the Gaussian distribution of laser beam. The Gaussian peak of incident light coming into the one side of such component at the central part, may go out from the other side of component near the peripheral part, conversely, the skirt of Gaussian beam combing into the peripheral part may go out of the central part. Thus, the beam shaping is obtained with the component of cone axicons and therefore the superresolution can be realized in a confocal imagin system. Meanwhile, the energy loss is much diminished and the optical power deserted hitherto is recovered.

Combination of Integrated Optics and micro-machining technologies offer immense potential for sensor applications. Small mechanical deformations can often produce considerable changes in optical properties of devices resulting in drastically improved sensitivities. Here we prose and analyze a novel pressure sensor consisting of integrated optic Mach-Zehnder interferometer whose sensing arm is fabricated on a silicon micro-machined diaphragm. The analysis consists of determining the changes in optical output corresponding to the diaphragm deflections due to impressed pressure. Dynamical equations of motion are solved and resulting displacement fields are related to refractive index and optical path length changes of the Mach-Zehnder interferometer. Results can be used to obtain the change in sensitivity due to change sin path length and refractive index variations. The analysis can easily be applied to other MOEM sensor devices like those consisting of micro-machined vibrating cantilevers and bridges controlling optical waveguides, directional couplers or multi-mode-multi-waveguide structures.

An IR sensor with the lead-titanate (PbTiO₃) thin-film and thermal isolation improvement structure using the technology of micro-opto-mechanical system has been designed, fabricated and developed. In this paper, both numerical analysis of the static operation mechanisms such as the effects of IR light power on the depletion layer width and voltage drop across the thin PbTiO₃ film, and the dynamic responses of a thin-film pyroelectric sensor to sinusoidal modulated radiation are reported and compared to the experimental results. The fitting is quite well. The major IR-sensing par ton the cantilever beam of the developed sensor consists of a 50-nm PbTiO₃ layer deposited by RF sputtering, and a gold layer evaporated as an IR radiation absorber. With active cantilever dimensions of 200 X 100 X 5 micrometers ³ formed by etching processes, the cantilever structure exhibits a much superior performances to that of a traditional IR-sensing bulk structure under the 800-(mu) W incident optical light with wavelength of 970 nm.

This paper reports the design, fabrication, and testing of a Micro-opto-mechanical grating/mirror switch driven by electrostatic actuator for fiber-optic switching applications. It consists of two banded silicon wafers. One input fiber with a hemispherical lens at its end and three photodetectors are fabricated on the upper wafer. A movable platform with two gratings and one mirror are fabricated on the lower wafer. When the movable platform is at a certain position, the input beam can be split into three beams by the gratings. Details of the grating switching design, theoretical analysis, fabrication and experimental results are presented in this paper.

With the emergence of new trends in optical communication and sensing syste, the importance and need for novel concepts such as diffractive gratings that can be implemented on a microscale has become a thrust area of research. In this paper, we compare various grating structures and their suitability for MEMS applications. The design approach, analysis and integration into optical systems are discussed in the context of both fiber and planar waveguide technology. Also, the differences and similarities among these methodologies using silicon micromachining are brought out. Parameters of interest, such as efficiency of micro-grating structures and ambient effects that influence the performance of the devices/systems are also discussed.

In this paper, some advantage on testing method for optical supersmooth surface using Atomic Force Microscope (AFM) are presented, and compared with classical interference method. Important applications of AFM for optical technique are introduced in the paper. Some testing results on microprofile and roughness of optical supersmooth surface using AFM method are listed, and it has indicated that result is not obtained with interference method.

THere is an increasing necessity to record the deformation characteristics of microelements due to their increasing demand for engineering applications being used in the automotive industry, micromachines, special sensors etc. The data required are either thermal or mechanical such as Young's moduli, stress-strain values, creep-, fatigue- and fracture data. In this investigation two non-contacting laseroptical strain sensors are being used to determine deformation data in combination with a special designed microtensile machine. The laseroptical strain sensors are applied to determine non-contacting strain values including a laser interferometric system with a high spatial resolution and a laseroptical speckle correlation method with high resolution.

In this paper, two quantitative methods to measure micro- deformation using gratin microscopy are proposed, a grating diffraction method and a full-field grating phase shift method. A compact optical transmitting microscope with white light source is reconstructed by developing a loading and recording system. For direct strain measurement, a grating diffraction method is presented. With the help of a Bertrand lens, the Fourier spectrum of the grating is formed on the CCD sensor plane with high image quality. Software for precise, fast and automatic determination of the diffraction spot centroids is developed. Local strains are thus measured with high resolution. For the deformation measurement, a phase-shifting grating microscope method with high sensitivity and spatial resolution is proposed. Phase shifting is based on the slab refraction effect and is realized via a tilting compensator. The system possesses a high spatial resolution, and a displacement precision of 0.1 to 0.03 micrometers . The combination of the grating diffraction method and the phase shifting method in the same test provides simultaneous measurement of strain and displacement, thus demonstrating that the grating techniques are viable in the microscope environment.

The general idea of the presented investigations is to use the polarization of the electromagnetic field in high- resolution optical microscopy to get information about sub- wavelength details of topographical structures. The main application is the localization of vertical edges. For structures in non-magnetic materials, polarization effects are caused by the different boundary conditions for the tangential and normal electric field components. Using rigorous numerical simulations we show that two physical- optics model describe the polarization dependent images of vertical edges and sub-wavelength structures: a boundary diffraction wave originating from the tip of the edge and waveguiding effects, respectively. We report on two experimental approach for polarization usage: a) comparison of interference microscopy images for s- and p-polarization, and b) polarization interferometry. The former is capable of 'synthetical microscopy'. Measurements of well defined structures are compared with rigorous numerical simulations.

A high-precision measure scheme for half-wave voltage V_(pi ) of Y-tap MIOC is proposed. This scheme is based on Sagnac interferometer and a saw-tooth wave with special period is used. With this scheme, the temperature characteristics of V_(pi ) of a type of MIOC is studied experimentally. The result shows that its half-wave voltage is temperature-dependent. In the range of -10 to +55, the varying value is 0.162V, the temperature coefficient is 662 PPM/degrees C and the variation is linear and repetitive. Experimental study and detail discussion demonstrate that high accuracy can be achieved with this scheme and it is very suitable to be used in studying and calibrating V_(pi ) of the modulator used in close-loop FOG in-site.

The necessity to protect cultural heritage is indisputable. The paper present two important metrological problems connected with the assessment of the condition and behavior of two monumental structures located in mining-influenced area in Upper Silesia region. The first problem has been effectively solved through using laser tilt and vibration sensors designed at the Central Mining Institute's Laser laboratory, while the other is to be investigated by using acoustical holography to detect the structure of the castle's foundation and its surroundings in the ground. The paper present the experimental results obtained with the use of both methods. An analysis of the tilt sensor at the castle show special effects of its behavior which are to be related to other factors outside mining. These factors need further detailed investigation. The method of acoustical holography has been experimentally verified in detecting the model structure of underground workings.

In the present work, the thermo-mechanical behavior, temperature versus thermal deformation with respect to time, of different coating films were studied by a non-destructive technique known as shearography. Ceramic, i.e. Al₂O₃ as well as polymer, i.e. Epoxy, coatings on metallic alloys, i.e. carbon steels, were investigated at a temperature range simulating the severe weather temperatures in Kuwait especially between the daylight and the night time temperatures. The investigation focused on determining the in-plane displacement of the coating which amounts to the thermal deformation and stress with respect to temperature and time. Along with the experimental data, a mathematical relationship was derived describing the thermal deformation and stress of a coating film as a function of temperature. Furthermore, results of shearography indicate that the technique is very useful NDT method not only for determining the thermo-mechanical behavior of different coatings, but also the technique can be used as a 2D microscope for monitoring the deformation of the coatings in real-time at a microscopic scale.

In this paper, a non-destructive testing technique, based on electronic speckle pattern interferometry, is presented to measure 4-point bending of wood. The mechanical behavior of the wood, such as Poisson Ratio can be obtained from the test result. To measure the out of plane displacement produced by 4-point bending, the wood specimen which is 33 X 3 X 3 mm, is secured in a special loading device. The loading device can produce 4- point bending symmetrically. The device with the specimen is put in a Michelson electronic speckle pattern interferometer assembly. Speckle pattern is produced on the natural 'rough' surface of the wood when illuminated by laser. A series of laser speckle interferograms are captured by a CCD camera and then sequentially subtracted to reveal deformation of the surface. Correlation fringes can be obtained while the load is applied. Both experimental results and theoretical analysis are presented.

An optical fiber has been used in a wide area such as in communication system, a view guide for diagnosis, applied optical sensor, etc. In such applications of the optical fiber especially in the sensor, some new sensor may be expected. In this study, possibility of a speckle nose used sensor was discussed. For this, the speckle noise patterns were observed to make clear their characteristics with regard on the miss-match of optic axis and an experimental study was carried out on the influence of edge surface condition, core diameter and distortion. In addition, the speckle noise pattern was measured by using the digital image processing technique, and its characterization was partly made. From these investigations, the possibility of speckle noise used sensor was discussed.

Fiber Bragg gratings (FBGs) are considered excellent sensing elements for a number of applications such as load monitoring in civil structures. Over the past decade, significant progress has been made in FBG fabrication, interrogation and multiplexing. This paper briefly reviews recent progress on FBG multiplexing and applications with emphasis on the work conducted at the Hong Kong Polytechnic University.

Arrays of fiber bragg gratings can be embedded in engineering structures to study the effect of various deformations and perturbations and thus enabling its health monitoring. In this paper, two multiplexing and detection schemes useful in the case of high resolution Bragg Gratings are presented. Instead of the conventional detection schemes, like an array of non-uniform grating and wavelength based addressing or an array of uniform grating with time- delay based and distinguish the gratings from each other. The first technique uses continuous wave input and measures the reflected amplitude response, while in the second technique we input pulsed light and measure the height as well as width of the reflected pulse. In both the cases, a minimum response time is suggested for the measurement to be made. This is the time when responses from the last grating is also obtained and a high degree of saturation leading to stable condition is obtained. We have combined the results for a single grating using the coupled mode theory with an equivalent matrix operator for the array to obtain an effective and simple mathematical tool to handle the large array problem.

We report on the use of a frequency-domain reflectometry technique for multiplexing fiber Bragg grating (FBG) sensors. This technique is based on the modulation of light intensity from a broadband source by a swept-frequency RF carrier. Signals from the FBG sensors located at different positions in an array are separated in the frequency-domain and demodulated using a tunable optical filter. A three FBG sensor system is experimentally demonstrated. The potential of the technique for multiplexing a large number of FBG sensors is discussed.

A unique structure of microbend optical fiber sensor (MOFS) for measuring tensile and compressive strain is described in this paper. The average measuring sensitivity for tensile strain is 35 (mu) (epsilon) using 3 MOFS arrays. The repeatability and stability of MOFS are better than 18 (mu) (epsilon) . The loss sensitivity of single-mode (SM) fiber and multi-mode (MM) fiber used in MOFS, as well as the relationship between the pulse width of diode laser and loss sensitivity are also studied in this paper. From these studied, some conclusions have been obtained. There are 1) the los sensitivity and repeatability of SM fiber are better when compared to MM fiber in MOFS, and 2) the variation of pulse width of laser would only influent the signal-to-noise ratio and dynamic range, but has no contribution to loss sensitivity. Experimental result also show that loss of SM fiber highly depends on the wavelength of laser, but MM fiber has no such property. The loss of Sm fiber between the wavelength of 1550nm and 1310nm is about the ratio of 6.5. Therefore, the experiments reported in this paper used wavelength of 1310nm to measure tensile strain and 1550nm to measure compressive strain based on the above property of SM fiber, without changing the configuration of MOFS.

Two kinds of fiber optic vibration sensors for civil structure vibration monitoring are proposed in this paper. The first is based on the detection of spatial mode speckle of a multi-mode optical fiber. A multi-mode optical fiber, diameter is 200/230 micrometers , is used in the present experiment. The second method uses an e-core two-mode optical fiber. The experiment on a composite beam with an embedded statistical fiber optic sensor and surface mounted e-core two-mode fiber optic sensor are demonstrated. The experimental results show that the two types of the fiber optic vibration sensor have higher sensitivity compared to piezoelectric sensors along with other benefits of fiber optic sensor, including lower cost.

To ensure the safety and integrity of tied arch bridges, it is crucial that tension levels in cables do not exceed their design levels. Currently, visual inspection is required since there are no reliable techniques that can accurately determine the tension levels of these cables. A possible approach would be to correlate the vibration measurements with the tensions in these cables. However, due to their long length, access to these cables for mounting contact sensors is not easy. An attempt has been made to use a He/Ne laser vibrometer for non-contact cable vibration measurements on a tied arch bridge. The objectives of this test are to assess the quality of vibration measurements from the He/Ne laser under regular daylight environment and to determine the vibration signatures of these bridge cables under ambient condition. The results of study indicate that using non-contact measurements, a quick and easy prediction of tension levels in bridge cables can be made. This paper presents the results of the study and presents discussion on the advantages of non-contact measurements and possible testing difficulties.

Design of simple, low cost optical sensors for continuous liquid level measurements is discussed. The sensor consists of only a source and a photo-receptor placed in a cylindrical tube containing the liquid. Various parameters of this simple package are selected through diffraction calculations.

Beginning from low level concepts, the basic physics behind the optical excitations of surface plasmon polaritons by volume electromagnetic wave under resonance prism coupling condition using both Otto and Kretchmann configurations is explained. Various changes to surface plasmon resonance profile due to any modification occurring at metal/dielectric interface are discussed. Organic thin film of Calix resorcinarene are deposited on gold coated glass slides by spin coating technique. The surface plasmon resonance angle shift due to this organic layer as compared with bare gold film predicts the sensitivity of surface plasmons to any modification occurring at the metal/dielectric interface. Investigations ar made to study the change of ambient close to the film. By the changing the layer system from glass/gold/calix/air to glass/gold/calix/water, the SPR curve is greatly changed. Exploitation of these changes on designing different optical sensors are reviewed. Finally a short summary of potential device application is given.

In our research, the glass was used as a substrate for H⁺ ion sensitive field effect transistor (ISFET). The sensitive characteristics of five structures for separative extend gate ion sensitive field effect transistors were studied, which include tin oxide/aluminum/micro slide glass, tin oxide/aluminum/corning glass, indium tin oxide (ITO) glass, tin oxide/indium, indium tin oxide glass and tin oxide/micro slide glass. Indium tin oxide thin film is the first time used as a H⁺ ion sensitive film which has a linear pH sensitivity of Nerstern response, about 58 mV/pH, between pH2 and pH12. In addition, the sensing area effect of the tin oxide/glass, tin oxide/ITO glass and ITO glass structure which without Al conductive layer will be discussed.

The signals between cascaded Fabry-Perot sensors have serious cross-talk problems due to complex phase interactions between sensors. However, cross-talk mode in cascaded Fabry-Perot sensors can be employed for demodulating optically differential-phase in a path-matching differential interferometry. This paper present a novel design in two series Fabry-Perot sensors for a differential- phase measurement analyzed by an optical spectrum analysis. The spectrum transfer function in a light source and Fabry- Perot cavities are simulated by a Gaussian distribution spectrum and a low-finesse reflectivity, respectively. It shows that two series Fabry-Perot sensors with the differential-phase measurement can be designed accurately. Experimental data shows that the novel design in measuring a differential-phase between two series Fabry-Perot sensors is achieved. This design in two series Fabry-Perot sensors for a differential-phase measurement can be applied to unbalanced system detection or noise compensations.

An Amplified Closed-Sagnac Loop Interferometric Fiber Optic Gyroscope (AC-IFOG) has been proposed. It is constructed from an open-loop interferometric fiber-optic gyroscope with an erbium-doped fiber amplifier (EDFA) that closes the sensing coil into a re-entrant configuration. Earlier experiments have shown a 6.56 fold increase in rotation response factor at a rate of 5 degrees over a conventional gyroscope using the same fiber length and light source. This paper reports the theoretical analysis of its operation. The analysis has been focused on the effect of the EDFA inserted within the re-entrant path. The analysis shows that the rotation detection factor can be increased by at least two orders as compared to a conventional IFOG when the EDFA is an ideal device. A mathematical expression for the open-loop response has been derived and it agrees well with the experiment result.

Intensity based fiber optic pressure sensor has been fabricated using micromachining technology. The sensor consists of a multimode fiber bundle and a 100nm-Au/30nm- NiCr/150nm-Si₃N₄/300nm-SiO₂/150nm- Si₃N₄ diaphragms supported by a micromachined frame-shape silicon substrate. The distance between the fiber bundle and the diaphragm of the pressure sensor is 900 micrometers . Three fiber optic pressure sensor having different size diaphragms were fabricated and used in experiments. The pressure sensitivities were 20.69 nW/kPa, 26.70 nW/kPa, and 39.33 nW/kPa for the pressure sensor with diaphragms of 3 X 3 mm² area, 4 X 4 mm² area, and 5 X 5 mm² area.

Scattering of light by random rough surface scan be numerically simulated by using an exact electromagnetic scattering theory. Unfortunately, the characterization of surfaces is almost impossible owing to the non-uniqueness of the inverse scattering problem and highly nonlinear relationship between the surface parameters and the scattering. Thus, existing practical methods for qualitative or quantitative characterization are almost entirely experimental. Here we apply neural networks for estimating statistically the surface parameters. Previously, we have successfully demonstrated that neural network as a statistical estimator for optical scatterometry is an efficient tool for characterizing periodic microstructures. We generate numerically random surfaces, which are characterized with the degree of roughness, i.e., rot-mean- square (rms) amplitude of the roughness and correlation length. Here we are mainly interest in the most demanding region of the rms amplitude in the so-called resonance domain, corresponding to height fluctuations and correlations up to 5 times the wavelength of light. The neural network model, which is her a self-organizing map, is first trained and calibrated with the known surface parameter and scattering data pairs. At characterization stage, using only measured intensity distributions, the neural network theory classifies surface parameters into discrete classes of the rms amplitude and the correlation length. For most cases the classification result deviates at most one class, corresponding to 0.5 wavelengths, from the correct values.

A novel optical displacement sensor based on Bragg effect is described. A green light bema was used to excite a Rh6G dye solution in Shank type geometry. The beam was split up by a dielectric mirror and the two equal intensity vertically polarized light beams were folded by two mirrors to interfere in the dye cell. The lasing wavelength was found to be a precise function of the half angle between the beams. The vibrating body was attached to one of the folding mirror. In normal operation the lasing line wavelength was unchanged but during mirror vibration corresponding to this 1 degree was 87 micrometers . The sensor resolution was about 1.3 angstrom/micrometers . This ultrashell displacement sensor can be used to determine the frequency of vibration or simple displacements in ultraprecise applications.

In this paper, we report a Sagnac interferometer based velocimeter with a resolution of 0.3micrometers /s. The sensor is constructed from commercially available telecommunication single mode fibers. A sensing probe is inserted on one side of the Sagnac loop to illuminate a test surface and to couple light back to the coil. Nonreciprocal phase shift appears between the counter-propagating waves when the surface is moving away or towards the sensing probe. A number of single-no-noise-ratio enhancing techniques have been employed and a nanopositioner is also used to provide a known velocity to test the sensor response. Our experimental result have shown a linear relationship between the applied velocity and the senor response within the nanopositioner restricted measurement range of 20micrometers /s.

Because of the pH sensitivity is one of the important characteristic parameters of ISFET devices. The response of ISFET is mainly determined with the type of the sensing membrane, therefore the sensing material plays a significant role. In addition, the hysteresis is the non-ideal and unstable factor of ISFET devices for measuring. Hence, in this study, the pH sensitivity and hysteresis of a-WO₃ gate ISFET are investigated, and compare with different sensing membranes.

This paper presents a new approach to develop an optical fiber refractometer. The objective of the study is to come up with a relatively inexpensive but reliable refractometer that can be used to measure the change of refractive index in a resolution of 10^-5 and to work in a dynamic range up to 6 X 10^-3 at a DC frequency up to 100 Hz. It is known that the phase modulations of optical fiber sensors are very sensitive to external disturbances, especially to the effects of thermal drifts or vibrations. A cancellation technique to compensate the effect of variation on a PZT stack is proposed in this paper to stabilize the system. Two parallel Fabry-Perot sensing cavities corresopndin to two path-matching cavities for read-out systems are employed to form path-matching differential interferometries. One Fabry-Perot cavity is used as sensing head, and the other as reference sensor. As a result, the experimental data show that the change of refractive index of a so-designed sensing system can be kept in at the level of 10^-4 without any serious variations even for a three-hour long-term monitoring. Accordingly, the proposed new system can be easily implemented, and used as a long- term monitoring system in medical care environment.

In planar diffractive imaging system, extra-axial imaging elements are frequently used. Since the elements have large off-axial aberrations such as coma, astigmatism, field curvature and distortion, it seems a little difficult to design a practical aberration-free element. In this paper, we reviewed the axial imaging diffractive element design procedure. Referring to designing axial elements, we present a semianalytical approach that enables one to determine the exact surface profile of an extra-axial element based on geometrical optics according to design and aberration-free requirements. The design procedure of the element can be divided into two steps: firstly, to obtain the zone boundaries and then to solve the exact surface profile. Finally, a schematic is given to test and evaluate small size diffractive elements.

In this work we investigate the interaction between rectangular-grooved transmission gratings and a resonant plasma layer at IR wavelengths. The gratings are designed to convert quasi-vertically incident light into quasi- horizontally propagating light in a high refractive index GaAs substrate with efficiencies of almost 90 percent in the first diffraction order. This can only be achieved by etching highly asymmetric '(lambda) /4' or '(lambda) ' gratings in a high refractive index material evaporated on the GaAs substrate. The resonant plasma layer (RPL) consists of a very thin highly doped n-GaAs layer whose plasma frequency is almost equal to the frequency of the incident light. Under these conditions Drude's formula shows that the refractive index almost vanishes due to plasma oscillations. The interaction between the diffraction modes and the RPL are investigated and optimized on the base of a rigorous coupled-wave analysis. This analysis reveals to which extent the RPL can influence the distribution of light between the zero and first diffraction orders. In the optimum position of the RPL, the first order diffraction efficiency changes from 90 percent down to 25 percent for a RPL thickness change of 40nm.

Consumers' demand for small, portable, increased functionality, more powerful and lower cost products has been the driving force in the technological advances of electronics packaging. This pushes the trend toward the development of smaller and higher power electronic packages. Due to the coexistence of variety materials with different coefficient of Thermal Expansion in the electronic packages, reliability becomes a concern, especially with smaller package sizes. The thermal mismatches often result in the delamination of interfaces between two materials, which eventually leads to ultimate mechanical and/or electrical failure. With its unique combinations of high sensitivity, optical contrast, range and good spatial resolution, Moire interferometry technique has increasingly been employed in the analysis of thermal deformation in electronic packages. However, with the commercial available moire interferometer, spatial resolution of the system leaves much to be desired. The inability of commercial moire interferometer to monitor local deformation such as at the die attachment level or the die corner thus limits deformation studies at those critical areas.

Detailed tunneling current measurements using a tunneling microscope tip have been performed on semi-insulating GaAs surfaces as a function of illumination power, Pt/Ir tip- surface distance, and separation between the tip and In/Ga electrode on the sample surface to elucidate previously unsolved problems of illumination-induced thermal expansion effects on the probe and of the surface depletion effects. We show that the tip-sample distance to detect a constant tunneling current is extended with increasing the otpical excitation power. It is also found that the photo-induced tunneling current as high as 8 nA driven by a 746 nm laser diode is linearly proportional to the optical excitation power. This photo-induced carriers conduction is also confirmed by studying the transient photocurrent responses, which is slowed down by increasing the tip-to-electrode distance. These results reveal that, in our case, the thermal effects are negligible and photogenerated electron tunneling is a dominant mechanism for the increased tunneling current from the samples surface biased at negative voltages relative to the tip.

Beam transform, such as to obtain uniform focal spot with flat top, steep edge, low side lobes and high light efficiency, can be realized well by diffractive optical element (DOE). The DOE has many advantages, such as high light efficiency and strong phase distribution design flexibility. To increase the light efficiency and decrease large-angle scattering, continuous phase DOE should be used. The phase design is competed by a kind of multi-resolution hybrid algorithm based on hill-climbing and simulated annealing, which exploits sufficiently strong convergence ability of the hill climbing and global optimization potential of the simulated annealing. A kind of phase distribution with good geometrical structure and diameter 80 mm is obtained by choosing disturbance function, receipt and refused probability and so on. The simulated results show that the light efficiency is more than 95 percent, and the non-uniformity is less than 5 percent. Because the etching depth is direct proportion to the exposure time, to obtain continuous phase DOE, a kind of hollowed-out mask, namely gray-scale mask is used to control exposure time of each are. The mask is manufactured by linear cutting machine. The continuous phase DOE with diameter 80mm is fabricated by ion-etching with the mask. Finally, the tolerance of manufacturing error including depth error and alignment error are analyzed.

A micro-optics element has been designed for diverting unwanted harmonic waves out of high power laser system to perform Inertial Confinement Fusion (ICF). Based on scalar diffraction theory, a basic structure of color separation gratings (CSG) has been designed, which almost meets the request of ICF target system. To increase the diffraction efficiency of third harmonic wave at 0.351 micrometers and decrease that of fundamental wave at 1.053 micrometers and second harmonic at 0.527 micrometers , the basic CSG structure has been optimized by a hybrid algorithm based on simulated annealing algorithm and hill-climbing algorithm. During the optimization procedure, the freedom variable is the step width and step height in one period and the degree of freedom is totally four. By applying several different bounds for objective function, several optimized micro- optical structures have been obtained, which all meet requirements of ICF target system. The influences of step width errors, step height errors and mould collimating errors of the optimized CSG have been analyzed respectively. Among these schemes, a most ideal structure has been selected which is most insensitive to fabrication errors. Under given error limitation, the diffraction efficiency's root-mean-square value at zero order for selected CSG have been investigated by statistical method.

The dynamic and spectral responses of a micromachined Fabry- Perot interferometer (FPI) subjected to an electrostatic force have been simulated. The FPI features a circular corrugated diaphragm supporting a flat thin film coated optical mirror that can be driven by four electrodes. These four electrodes serve not only to fine adjust the parallelism but also to tune the air gap between the mirrors and hence the characteristic wavelengths of the interferometer. Regarding to the dynamics response of the flat diaphragm, we consider a force balance among the squeezing-film damping, the spring force of the corrugated diaphragm, the inertia force of the flat diaphragm, and the electrostatic attraction force. The spectral response of a novel FPI based spectrometer that consists of two FPIs in tandem has been modeled and simulated. Contrary to the second-order oscillation normally existed in a mass-spring- damper system, for the current system, and dynamic of the optical mirror released from a pre-deflection displays an over-damping effect, which depicts the simulated mirror deflection as a function of time relaxing from a 6 micrometers pre-deflection effect, which depicts the simulated mirror deflection as a function of time relaxing form a 6 micrometers pre-deflection. This interesting phenomenon may exist pervasively in various micro-systems due to its higher area to mass ratio compared to that of the macro-systems. Our simulated result demonstrates that the tandem FPI based spectrometer, in principle, is able to obtain a spectral response with high accuracy from a light source having continuous spectrum.

The spectral characteristics of a diode laser are significantly affected due to interference caused between the laser diode output and the optical feedback in the external-cavity. This optical feedback effect is of practical use for linewidth reduction, tuning or for sensing applications. A sensor based on this effect is attractive due to its simplicity, low cost and compactness. This optical sensor has been used so far, in different configuration such as for sensing displacement induced by different parameters. In this paper we report a compact optical sensor consisting of a semiconductor laser coupled to an external cavity. Theoretical analysis of the self- mixing interference for optical sensing applications is given for moderate optical feedback case. A comparison is made with our experimental observations. Experimental results are in good agreement with the simulated power modulation based on self-mixing interference theory. Displacements as small as 10^-4 nm have been measured using this sensor. The developed sensor showed a fringe sensitivity of one fringe per 400nm displacement for reflector distance of around 10cms. The sensor has also been tested for magnetic field and temperature induced displacement measurements.

The need for quality control has lead to the implementation of automatic surface inspection systems, which have improved on-line monitoring of surface quality. Enamelled copper wire, cable and optical fiber are three examples where surface quality is very important. An extensive literature review conducted by the authors, has shown that with the current state of technology, there is much room for improvement in the field of non-destructive defect detection for enamelled copper wire. In this paper, the authors describe an IR light based surface inspection system which has been developed for non-destructive defect detection on cables, optical fiber and specifically on enamelled copper wire. Finally, results from extensive trials at an enamelled copper wire manufacturing company are presented and compared to a simulation, of the defect detection head.

On-line monitoring cracks development of the aircrafts in active service is of great significance for flight safety. Fiber optic sensor has its unique advantages over conventional sensors in this aspect. For modern aircrafts, many critical structures are made of aluminum alloys. When structural damage occurs in structures due to cracking, it reduces the stiffness. This charge is reflected in the structure through changes in its dynamic characteristics such as natural frequencies, modal damping. In this paper, the ability of surface mounted fiber optic polarimetric sensor on aluminum vibrating cantilever specimen to detect cracks is studied. Different sources such as He-Ne laser, LD for fiber communication, laser pointer with longer, shorter and very short interference lengths are used in our experiments to evalute their ability for dynamic test, respectively. The preliminary experimental results show that the measured main frequencies will be different for various number of cracks and depths. The three sources, the drift of light intensity and the change of interference contrast will not affect the measured main frequency values. Some of theoretical analysis is also given. From these results, surface mounted fiber optic polarimetric sensors is expected to find its application in monitoring structural integrity of structural members of aircraft in active service.

We describe a spectrally resolved white light interferometer with polarization phase shifter for use in surface profiling. Phase shifting is introduced by a rotating half- wave plate. The phase shifted intensity values needed for the phase calculation at each pixel are obtained from the same pixel instead of different pixels, thereby avoiding error due to variation in sensitivities of different pixels.

Defect of external outlines of wire rods which running at speed of 100 m/s need be measured in process of production which high-speed wire rods in iron and steel industry. At present, it adopts mainly method of rotation which measure section shape. This article will introduce a kind of disposal plan which high-speed camera and picture by multi- detector. This article will analyze that number of calculation detectors and range of measurement which defect of outline, and advantages and disadvantages which in comparison rotation plan with multi-detector plan. It proved the accuracy of the analysis by simulated test.

This paper presents a new optical transformer which can measure high voltage and large current simultaneously. The measurement of voltage is based on the Pockels effect. A novel structure is posed to realize an optical voltage sensor which has better stability. The measured high voltage is directly applied on the optical voltage sensor without using any capacitive voltage divider. The measurement of current is based on the Faraday effect. A bulk glass closed- loop structure for optical current sensor is used. The optical voltage sensor is in the middle of the HV polymeric insulator which is full of SF₆ gas, and the otpical current as immunity of electromagnetic interference, no saturation, no oil inside, wide band range, excellent transient characteristics and light weight etc. The principles, structures and testing results of the combined optical voltage and current transformer are described in this article.

Optical Current Transducer (OCT) is a ne kind of transducer applying in electric power measurement system. This paper analyses the questions of temperature offset and noise affection in measuring DC current with OCT. The solutions to these questions are described in this paper. One is adopting AC modulation technology to overcome temperature offset. The other is an adaptive filter algorithm which is used in OCT to refrain noise. It is proved by experiments that the two methods are effective and can improve the measurement accuracy.

Laser Doppler vibrometers are widely used to obtain velocity information from vibrating targets. Doppler shift of the light scattered from a vibrating target is detected by using heterodyning with a reference beam. To obtain high spatial resolution and high intensity of the backscattered light and to produce speckles of large size at a photodetector plane the target is placed in the waist of a probe laser beam. At that target position the curvatures of the wavefronts of the reference beam and the scattered light can be different. The difference in the wavefront curvatures result in mismatching of wavefronts of the heterodyning beams and decreasing in the Doppler signal amplitude.

In the research, we simulated the temperature characteristics of the a-Ta₂O₅ ISFET by the Gouy- Chapman-Stern theory. The values of the pK_a and pK_b would be induced to calculate the temperature coefficients of the a-Ta₂O₅ ISFETs for predicting the behaviors of the a-Ta₂O₅ ISFET under different temperatures. In the experiment we used the method finding the V_GS values of the experimental curves by fixed I_DS value to get the pH sensitivities at different temperatures. By using the same way we could change the temperatures to find the temperature coefficients in different pH solutions. The relationship of the pH sensitivities of a-Ta₂O₅ ISFET versus the temperatures were the linear. Oppositely the curves of the temperature coefficients is not linearly obviously.

The ion-sensitive field-effect transistors (IFSETs) with hydrogenated amorphous silicon were fabricated. In this paper, the hydrogenated amorphous silicon acting as sensing membrane was used to investigate the pH response of a-Si:H ISFET. The I_DS-V_G curves were carried out by I-V measuring system. The basic parameter of a-Si:H ISFET, namely sensitivity was obtained from I_DS-V_G curves. It exhibited a superior pH response of 50.6 mV/pH at temperature of 25 degrees C. Moreover, other characteristic parameters such as hysteresis and drift were proposed. Finally, the effects of operating temperature on sensitivity and drift were presented.

Optical measurement technique is widely used in length measurement, such as laser interferometers and electronic distance meters. The correction of air refractive index is necessary because the optical path length should be converted to the geometrical length in most vases. In order to obtain an average refractive index through the optical path, Edlen's formulae have been widely used with environmental measurements of air temperature, pressure, humidity and carbon dioxide concentration. In recent days, more precise formulae for calculating a refractive index of air have been desired in IR region. However, the measurement accuracy for near IR region is not sufficient.

Laser diodes (LDs) have been served as light sources of a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed with their practice and application. A two-wavelength laser- diode interferometer is elaborately demonstrated with current control of duel LDs in opposite directions to extend the range of interferometric measurements. The wavelength is controlled by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. A feedback interferometer with electronics is used to lock the interferometer on a preset phase shift to ensure the measurement accuracy. The interferometric techniques with laser diodes have been applied to an optical radar such as a single detection of multiplexed phase objects and to a distance measurement.

The 'optoelectronics industry' is a collection of six or more distinct industries that all depend on OE technology. The major markets are in communication, imaging, storage and displays. This paper gives a brief overview of the anticipated paradigm shifts, the potential markets and the promising new technologies in various OE markets.

The development of vertical-cavity surface-emitting lasers (VCSELs) has led to new types of low power, high efficiency light sources for data communication. The small size, low power, and surface-normal emission of VCSELs has enabled relatively dense 2D arrays for highly parallel data communication and optical signal processing. In this paper we examine the issues of device scaling volume down to minimum sized dimensions, and what device schemes may be required to obtain the scaling. Laser rate equations are used to show that when the VCSEL mode volume is reduce to wavelength cubed dimensions, a significant improvement in modulation speed is predicted based on the radiative lifetime change due to the Purcell effect. However, several parasitic effects must be controlled in order to realize these benefits. Most important are control of the optical loss due to diffraction or scattering, and control of the electronic losses due to carrier diffusion and surface effects. Novel optical confinement schemes based on oxide- apertures, photonic bandgaps, and/or closely coupled 2D arrays may be useful for controlling optical loss, while self-assembled quantum dots are attractive for controlling electronic diffusion to dimensions within the minimum optical mode volume.

A microscopic many-body theory for the nonlinear optical response of semiconductors is reviewed. The importance of Coulomb interaction induced carrier correlations is demonstrated in excitonic pump-probe spectra. The influence of excitonic and biexcitonic contributions to coherent pump- induced absorption changes at the exciton frequency are discussed. Absorption changes induced by incoherent exciton and unbound electron-hole populations are studied.

This paper discusses the role and impact of advancements in Photonics Technology on the performance enhancement of guided missile weapon system with specific reference to the development of Indian guided missiles program. India is emerging as a technologically strong nation with core competence in Space, Missile and Nuclear technologies, advanced computing including supercomputers and software. Based on the realization of the fact that high technology strength is the key to economic prosperity and military strength, India is progressing several high technology areas that help in attaining the global competitiveness. Photonics is identified as one of the important ares in this direction and hence high priority has been accorded for R and D in Photonics. This paper reviews the current trends and developments in missile technology and highlights some of the important developments in Photonics that have a force multiplying effect on the performance enhancement of guided missile systems.