A reliable and cost effective fibre optic oxygen sensor for monitoring of human breathing has been developed using a normal 200μm silica core/silica cladding optical fibre and a polymer sensing matrix. The fibre optic oxygen sensor is based on the fluorescence quenching of a fluorophore by oxygen. The sensing matrix, containing immobilized Pt(II) complexes, was coated at the end of the silica core/silica cladding optical fibre. The sensitivity and time response of the sensor were evaluated using the method of luminescence lifetime measurement. The polymer substrate influence on the time response of the sensor was improved by using a fibre taper design, and the response time of the optimized sensor was less than 200ms. This silica fibre based optic oxygen sensor is suitable for monitoring of patient breathing in intensive care unit in terms of safety and low cost.

A sensor head consisting of a photonic crystal fiber (PCF)-based Mach-Zehnder interferometer (MZI) and a fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature. The MZI fabricated by splicing a short length of PCF between two single-mode fibers with the air-holes structure completely collapsed near the splicing points, is sensitive to fiber bending and surrounding temperature, while the FBG is only sensitive to the later. Simultaneous measurement of curvature and temperature is therefore obtained. Sensitivities of 4.06 nm/m^-1 and 6.30 pm/°C are achieved experimentally for curvature and temperature, respectively. And the corresponding resolutions are 5.2x10^-4 m^-1 and 1.25 °C for curvature and temperature, respectively, based on the wavelength measurement resolution of 10 pm.

An optical current sensor with adjustable sensitivity is proposed and investigated in experiment. A single bismuth germanate crystal is used as both current-sensing element and electro-optic modulator. When a rectangular pulse modulating voltage is applied to the crystal, the current-sensing signal can be obtained from the peak-to-peak intensity of output light. Both the measurement sensitivity and its temperature stability of the proposed sensor can be controlled by the modulating voltage, additionally its linear and monotone varying measurement range is larger than that of conventional optical current sensor. Direct current of ±(0.1~10)A was measured with electro-optically adjustable sensitivity, and maximum measurement uncertainty was less than 1.2%.

On the basis of the complex cavity model, the feedback-induced instabilities which may cause coherence collapse in single-mode distributed feedback (DFB) fiber laser sensors are analyzed. We measure the longitudinal operating mode and the frequency shift of DFB fiber laser due to Rayleigh backscattering, and obtain quantitative agreement between simulation and experiments in long-time investigations. All these study can provide references to design a novel form of DFB fiber laser sensor system utilizing external optical feedback, and the feasibility of the sensor has been proved.

Microcantilever as state-of-art sensor platforms has been widely investigated. Optical Fiber biosensors have the potential to provide cost-effective, real time, continuous, in situ measurements. The micro cantilever was fabricated on single crystalline SOI wafer using a series of side definitions and backside wet/dry etchings. Since the micro cantilevers are to be used as biosensor, 50 nm Au layer was deposited for the immobilized of bimolecular on the cantilever surface and for reflecting the beam of light back into the fiber, the different light intensities means different bimolecular concentrations. The lamp-house is 1310 nm super luminescent LED. Single mode fiber with gradient index lens as a collimator and 3dB 50:50 optical coupler was used to transmit light. PINFET was used to convert the reflecting the light intensities into electronic signal. The test results demonstrated that the optical fiber reflective read out microcantilever biosensor has high sensitivity, high dynamic response, a greatly reduced size and high precision.

In order to embed the fiber Bragg grating (FBG) into intelligent metal structures, a metallization of FBG is demanded. Ni-P alloy is usually deposited as a metal coating on FBG by coarsening fiber, which will give some bad influence on the property of fiber. So in this paper, a layer of Ni-P alloy was electroless plated on FBG without coarsening of FBG, and the surface morphologies, composition, structure and adhesion force of the coating film was characterized by SEM, XPS and XRD, respectively. The results indicate that the alloy clad was very smooth, flat and compact, and in amorphous state with a composition of Ni 71.73 at% and P 28.27 at%. Moreover, the temperature sensing behavior of FBG metallized with and without coarsening was compared, and a theoretical model of temperature sensitivity for Ni-P coated FBG was presented. It shows that the temperature sensitivity of FBG without coarsening increases was 0.01126 nm/°C, but 0.01098 nm/°C for the coarsened one. Clearly, metalized FBG with no coarsening showed better sensing properties.

A novel method of measuring the steam quality based on wavelength modulation surface plasmon resonance is proposed. The surface plasmon resonance is implemented using the Kretschmann geometry with an Au layer deposited on a BK7 prism. The steam quality can be determined from the measured resonance wavelength as well as the pressure and temperature of the steam. The results show the possibility of a real-time, high-resolution quantitative measurement of steam quality with the proposed method.

Self-mixing interferometry (SMI) signals are observed from a sensing system consisting of a laser diode with external optical feedbacks. SMI signals carry the information associated to both of the displacement and parameters of the SL. To retrieve the information precisely, pre-processing of SMI signals is the first key step. For achieving real-time, and high quality sensing, this paper proposes a Field-programmable gate arrays (FPGA) based filtering and normalizing processing for SMI signals. According to the noise features contained in SMI signal, a median filter and a wavelet transform based filter are combined for our design. Hardware co-simulation verified that the performance for this FPGA used filter design.

The optical coherence domain polarization (OCDP) system based on white light interferometry is used for the detection of distributed polarization mode coupling point in the polarization-maintaining fiber (PMF). Compared with existing OCDP, in order to detect the polarization coupling amplitude between the fast-axis and slow-axis of high precision PM fiber optic gyro ring, this paper presents a method of angular alignment for measuring polarization coupling in PMF used for OCDP. We add a light intensity detector and two alignment devices in the OCDP. We use the light intensity detector to detect the polarization of rotated PM fiber real-timely and use the two align devices to control the polarization of input and output PMF of fiber optic ring respectively. Based on the theory of Jones, we establish the simulation model of the polarization detection system so as to simulate the influence of different input or output polarization on light intensity; we also design the alignment system of PMF. The experimental results show that the above method can effectively achieve the polarization-maintaining fiber alignment, ratio of axial is 1°, measure the polarization coupling of optical fiber ring without optical fiber fusion splicing, and does not destroy the symmetry of sensitive ring. Overall, the method is simple and high precision.

An effect method for reducing the birefringence dispersion in Optical Coherence Domain Polarization (OCDP) is proposed in this paper. Based on an all-fiber OCDP system with a reversing mechanism before the polarization maintenance fibers (PMF), wide spectrum of light was launched into the testing PMF in the clockwise direction and counter-clockwise direction and we obtained the measurements of symmetrical two polarization-coupling. By processing the measurements, we reduced the length of the testing fiber to a half equivalently. The experimental results show that the amplitude resolution of polarized coupling in all-fiber OCDP system is -84dB, the dynamic range of measurement is 84dB and the spatial resolution is 49.3mm without the dispersion in PMFs. By this method, the measurement accuracy of the coupled position and amplitude in PMFs was enhanced, and the effects of birefringence dispersion were inhibited.

We have proposed a novel evanescent field (EF) sensor without any additional functionalized material. The sensors were fabricated by single mode fiber with a etched section on it. We study the properties of the optical intensities out of the sensors in the condition of immersing them in water, placing into a vacuum chamber or a climatic chamber. It was demonstrated that this EF sensors can senses the changes of the RI of water surrounding it. And the change of the output of the sensors occurs with a oscillation mode. We also show that the EF sensor with 11μm of outer diameter is sensitive to a change of RI with a magnitude of power of negative 7. Using this type of sensor, we demonstrate the vacuum sensing in the range from 20 to 300Pa. It is also demonstrated that the output of the sensors can be obviously attenuated by the scattering of the water vapor surrounding the sensing section. With adequate design of fiber, we believe that the new EF sensors can offer a platform on which the EF directly interacts with the materials of liquid or gas surrounding the sensing section and give the information of the changes in the RI of the materials and the scattering or obsorption to the evanescent field.

A reflection type polarization maintaining optical fiber temperature sensor was designed. The operation principle was introduced and the sensing equation was made. Analysis shows that the propagation loss variety is the main factor which will let the sensing equation parameters change. Compared the sensing equation and the expanded equation, the propagation loss coefficient can be separated with the sensor intrinsical parameters and a simple and practical field calibration method, with which the whole sensing equation parameters can be calibrated when certain temperature at the sensor probe was given, was proposed and the calculation equation was made. An experimental sensor system was built and the calibration experiments were done by change the propagation loss and the date obtained were analyzed and compared with polynomial fitting and model calculating. The result proved the field calibration technology and the sensing temperature precision can be better than ±0.5°C before and after calibration.

An inter-mode interferometer based on a simple single-mode fiber by core-offset splicing is presented. Through manually adjusting the horizontal displacement and the angle of two sections of core-offset fiber, we can achieve maximum interference spectrum. Then we add a reflector at the end of the last single-mode fiber. This reflector can lead the light to propagate twice in the offset single mode fiber structure so that we can get larger interference intensity, in the experimental process we see a better extinction ratio. The proposed method can find application in strain, temperature and vibration measurements and so on. By measuring the extinction ratio (ER) variation or wavelength shift of the interference pattern in this paper, sensitivity measurement can be achieved. The sensitivity of strain and temperature without reflector is respectively 10.38 pm με and 31pm/ °C. When reflector added, it can increase the sensitivity of the strain and temperature at a certain degree.

In order to suppress peak-to-peak drift in traditional phase generated carrier (PGC) demodulation, a novel ameliorated PGC demodulation algorithm based on differentiate and cross multiply demodulation (DCM) and sum of squares of orthogonal signals is proposed in this paper. This improvement has several advantages compared with the traditional PGC algorithm. The drift of the light power is eliminated and will not be transferred to the output. The noise from the light power is reduced much at the same time. Experimental results established by using dual-channel balancing detection technology and digital demodulation have confirmed the low intensity noise of the ameliorated PGC algorithm as expected as the theoretical analysis. The peak-to-peak value drift in the ameliorated PGC demodulation has been suppressed effectively. According to the experimental results, the demodulated amplitude and the test signal amplitude assumes certain linear relationship. The conclusion has the important reference significance to improve the performance of the system.

In this paper, we propose a new structure to measure the temperature and the concentration at the same time. Semiconductor absorption material is used for measuring the temperature; and fiber bundles are used as input and output fibers. Right-angle prisms, as reflectors, are used at the end of the fiber bundles. The concentration is measured based on the changing of refractive index.

An optimized design of a fiber optic flexible disk microphone is presented and verified experimentally. The phase sensitivity of optical fiber microphone (both the ideal model with a simply supported disk (SSD) and the model with a clamped disk (CLD)) is analyzed by utilizing theory of plates and shells. The results show that the microphones have an optimum length of the sensing arm when inner radius of the fiber coils, radius and Poisson's radio of the flexible disk have been determined. Under a typical condition depicted in this paper, an optimum phase sensitivity for SSD model of 27.72 rad/Pa (-91.14 dB re 1 rad/μPa) and an optimum phase sensitivity for CLD model of 3.18 rad/Pa (-109.95 dB re 1 rad/μPa), can be achieved in theory. Several sample microphones are fabricated and tested. The experimental results are basically consistent with the theoretical analysis.

This paper introduces an optical fiber based sensing system design for multi-layered pavement structural health monitoring. The co-line and integration design of FBG (Fiber Bragg Gating) sensors and BOTDR (Brillouin Optical Time Domain Reflectometry) sensors will ensure the large scale damage monitoring and local high accurate strain measurement. The function of pavement structure multi-scale shape measurement will provide real time subgrade settlement and rutting information. The sensor packaging methodology and strain transfer problem of the system will also be discussed in this paper. Primary lab tests prove the potential and feasibility of the practical application of the sensing system.

Technology on pavement monitoring has been paid more and more attention by government, engineers and scholars. Conventional methods, such as artificial inspection and core sampling, have defect in low efficiency and limited coverage, and modern technologies, such as spectrum analysis and integral imaging, have poor resistance to external interference and high cost, which reveals that common approaches have fallen behind the development of road engineering. Therefore, a novel raw material-encapsulated FBG strain sensor is put forward, thinking over outstanding advantages of fiber Bragg grating and perfect incorporation between coating layers and host layers. Numerical analysis and experiments have been done to inspect behavior of the sensing system. Results indicate that it can well detect the actual performance of pavements, and the sensor presents a high-precision, real-time and long-term monitoring, owning function of road disaster warming, which promise it an extensive future in pavement monitoring.

In this paper, a laser diode vibrometer based on the self-mixing interference effect is proposed. A prototype of the laser diode self-mixing vibrometer has been assembled and optimized. The self-mixing signals have been observed in the laser diode self-mixing vibration measurement system when the external object (PZT) is driven by function generator. Experimental result is given and discussed. The self-mixing vibrometer could reach high resolution with a wide dynamic measurement range up to 22 KHz.

To achieve higher accuracy, a new measurement method for noise suppression is demonstrated, based on two interleaved fiber Michelson interferometers which share the common interferometric-optical path by employing fiber Bragg gratings (FBG). One of the interferometers is used for monitoring environmental perturbations, which takes the advantage of the reflective properties of grating; the other is used for the detection of the real information under test including the environmental perturbations, which takes the advantage of the transmission properties of grating. Process the two signals using Lab VIEW based on PGC technique, to eliminate the environmental noise from the information, which is on the actual need to detect. The experiments show the random phase drift caused by environmental disturbances is eliminated effectively, improving the operation performance.

It is very important to monitor the lateral and axial strains of drilling riser for evaluation its health in deepwater. An optical fiber strain sensing system based on optical fiber Bragg gratings (FBGs) used for monitoring the strain of drilling riser is presented. The optical fiber strain sensors are made by embedding FBGs into thin columned fiber reinforced polymer which protect FBGs from seawater corrosion. Four optical fiber strain sensors are installed parallel to the riser axis and arranged at 90° angles around the riser by a home-made metal belt, at the same time, twelve resistance strain gauges are pasted near the sensors around the drilling riser at 30° angles as reference sensors. A scaled drilling riser about 1 meter long and 0.245m diameter is pressed in the lateral and axial direction in the range of 0-400KN, the experimental results show that the relative error between optical fiber strain sensors and resistance strain gauges is less than 6%.

An improved demodulation method by solving a quadratic equation was proposed for the phase generated carrier (PGC) scheme with frequency modulation to suppress the impact of laser intensity modulation (LIM). The influence of LIM on total harmonic distortion (THD) was analyzed for PGC algorithm considering laser intensity modulation coefficient (LIMC), signal amplitude, initial phase and modulation depth. According to our analysis, the maximum THD of PGC algorithm is more than -24dB when LIMC is 0.1. While the maximum THD is less than -65dB by using the improved method when LIMC is less than 0.5, which is limited by the low-pass filter. For an experiment system with 0.285 LIMC, the THD was -9dB for PGC algorithm. By using the improved method, the THD approached -50dB.

An integrated demodulation system of optical fiber hydrophone array is designed in the paper for the application of oceanic oil exploration. The characteristic of artificial seismic signal, sensed and collected by piezoelectric hydrophone sensor used in the actual situation, is analyzed by joint time-frequency analysis. Based on this, parameters of the optical fiber hydrophone sensitivity and modulation frequency are designed with redundancy, ensuring that the upper limit of dynamic range of fiber optic hydrophone demodulation system can meet the requirements in the same operating conditions of sea trials, as those of piezoelectric sensor system.

Mankind has been eager to know the variation of the atmospheric change processes in which the sun play a most important role, So research the Sun activity is a hot point. Observe and analyze its ultraviolet(UV) spectra is a valid way to know the Sun activity, solar UV radiation flux and upper atmospheric absorption of UV is representative of the sun activity. The solar UV emission lines are generally optically thin, so the detection aroused great attention. This paper provide an overview of the past two decades advances instrumentation for solar UV observation. Emphasis is given to the great mission such as OSO 8(Orbiting Solar Observatory 8), SOHO(Solar and Heliospheric Observatory), TRACE(Transition Region and Coronal Explorer), SDO(Solar Dynamics Observatory) and KuaFu, especially to their UV instrumentation and scientific objective, some outlook is proposed.

A fiber-optic curvature sensor based on the singlemode-multimode-singlemode (SMS) fiber structure is developed. Several notches in the transmitted spectrum of the SMS fiber structure are generated due to the multimode interference effect. The dependence of the wavelength shifts and intensity changes of three transmission notches on the applied curvature are different from each other. The maximum sensitivities of wavelength-curvature and intensity-curvature relationships are - 10.38 nm/m^-1 and - 130.37 dB/m^-1, respectively. By properly choosing to measure wavelength shifts or intensity changes, high sensitivity measurement of curvature over a large scale can be obtained. The wavelength of the second notch is insensitive to the curvature change, offering the possibility for simultaneous measurement of curvature and other parameters such as temperature or strain.

This paper researches the modular interference characteristics of polarization maintaining two-mode photonic crystal fiber (PMTMPCF) and proposes a new optical voltage transducer (OVT) for the electric power system based on modular interference in PMTMPCF. which uses a quartz crystal cylinder wrapped with PMTMPCF as the voltage sensing head, modulating the two interference output lobes' intensity of the PMTMPCF by making use of the converse piezoelectric effect of quartz crystal in high voltage end, while in low voltage end, using a PZT which wrapped with a piece of PMTMPCF to adjust the initial phase difference to orthogonal status. The experimental results show that the measurement accuracy can achieve 0.2% with good linearity.

Refractive index sensing characteristics of a polarization maintaining microstructured optical fiber (PM-MOF) Bragg Grating is investigated in this paper. Based on Finite Element Method (FEM) and the coupled-mode theory, the reflection spectrum of the PM-MOF Bragg grating is analyzed. The analysis results show that when the air holes are injected with analyte, the resonant wavelengths of the two polarization modes will drift. Furthermore the relationship between the difference of two polarization modes resonant wavelengths and the analyte refractive index is considered. The novelty of this work lies in the high stability of the fiber from that of two polarization modes responding similarly to the outside perturbation. Furthermore, the two center big air holes have great impact on the detection sensitivity. In order to select the most appropriate fiber, the impact of the central big air holes is discussed. The investigations in this paper provide the theoretical basis for the optical fiber biosensor.

A hydrogel coated long period grating (LPG) used as relative humidity sensor is investigated theoretically and experimentally. It showed a high degree of sensitivity when relative humidity was above 50%RH. For humidity levels from 50%RH to 72%RH, a wavelength decrease of 15.4 nm is seen, with a sensitivity of 0.66 nm /%RH. For humidity levels from 72%RH to 98%RH, a wavelength increase of 9.5nm is observed, with a sensitivity of 0.36 nm /%RH. For humidity levels greater than 65%RH, the transmission loss at resonance increases rapidly, showing a high degree of sensitivity of 0.53 dB /%RH and offering a high resolution of 0.02%RH. The proposed relative humidity sensor offered good repeatability and low hysteresis errors, with a standard deviation of 0.005dB/%RH and 0.26% hysteresis error while RH levels greater than 65%RH during three cycles of increasing and decreasing humidity. The stability test was also carried out and a standard deviation of 0.14%RH was obtained. In addition, the durability test showed that the humidity sensor can work at least ten months.

A Brillouin/erbium fiber laser (BEFL) of 25km single-mode fiber is constructed, and its characteristics of optical carrier suppression are measured and analyzed. Light wave modulated by an electro-optic intensity modulator (EOIM) with 11GHz microwave frequency is adopted as the testing light. As much as 32 dB optical carrier-suppression ratio is achieved at 112mW of 980nm pump power inside the BEFL. Meanwhile, the sideband powers remain nearly unchanged in the process. Moreover, the carrier-suppression ratio is precisely controllable by tuning the 980nm pump power in the BEFL. These optical carrier-suppression characteristics promise significant applications of such a technique not only to distributed Brillouin optical fiber sensing based on EOIM but also to microwave photonic signal processing.

This paper introduces a theoretical model which reveals the relation between the absorption and the refractive index of germanium within absorption region, which is crucial to a new fiber optic-semiconductor film temperature sensor developed lately in our lab. The new designed sensor is based on the effect of the temperature dependence of the refractive index of semiconductor. Many efforts on the effect of the temperature-dependent refractive index of semiconductor are reported in transparent region mostly by empirical model such as Sellmeier model[1]. We analyze the temperature dependence of the refractive index of semiconductor near the absorption edge other than in the transparent region. From the Kramers-Kronig relations, the refractive index is an integral of the absorption coefficient over the whole energy spectrum.Taking advantage of the model that explained the contribution of the integral cloesd to the absorption edge to the refractive index by Frank Stern [2] we are able to calculate the variation of the refractive index due to the thermal shift of absorption edge. The contribution of the temperature-dependent absorption coefficient to the refractive index is enhanced dramatically at the absorption edge of semiconductor, where the temperature dependence of the energy gap Eg can be used to get the absorption edge shift with Yu-Brook's model[3]. While the contribution of the absorption shift far away from the absorption edge to ▵n is negligible comparing to that near the edge according to Frank Stern[2]. Further demonstration experiments will be carried out to support our theory, in which refractive indexes of germanium are measured at specific wavelengths of 1310nm, 1550nm and 2000nm. Since the direct absorption edge of germanium is at about 0.82eV, corresponding to the wavelength of 1550nm, we estimate that the thermo-optic coefficient dn/dT of germanium at 1550nm would be larger than that at 1310nm and 2000nm.

A highly accurate Y-phase-modulater based fiber optic current sensor (FOCS) for alternating and direct currents up to 100kA was investigated. Reciprocal optical circuit and weak signal processing method based on related modulation and demodulation of this sensor were analysed. Models of the optical path system and signal processed circuit system were studied separately. And based on these models, the key temperature error sources and corresponding compensation measures were discussed. Furthermore, A 500kV engineering prototype and its performance test devices were designed, and type test of it was finished at Xi'an high voltage apparatus research institute co., LTD(XIHARI) by the end of 2010. According to the test results, the sensor achieved accuracy to within ±0.2% at -40 to 80°C with inherent temperature compensation, resolving power for small AC current was less than 0.5A, angle difference was less than ±2', and the overall performance exceeded the IEC60044-8 standard class 0.2S (±0.2%). Applications of the sensor are in high-voltage substations, in chemical chlor-alkali, and in the electrolytic production of metals such as aluminium.

In order to solve the problem of low reliability and strain transmission efficiency for optical fiber sensor packaged with epoxy adhesive, based on the particle diffusion mechanism, a system for metal bonding of optical fiber sensor was developed to research package technology of optical fiber sensor without adhesive. To improve the quality of metal bonding layer, orthogonal test of four levels was designed with four factors which were working distance, driving voltage, feeding rate, pressure of particle field and bonding strength between metal bonding layer and substrate was selected as the criterion of quality of metal bonding layer. The primary and secondary sequences of the influencing factors were acquired by the method of statistical analysis. The optimization results could be instructive to the research on metal bonding technology of optical fiber sensor.

We propose a novel embedded two elliptical cores fiber with a hollow air hole, and demonstrate the fabrication of the embedded two elliptical cores hollow fiber (EECHF). By using a suspended core-in-tube technique, the fibers are drawn from the preform utilizing a fiber drawing system with a pressure controller. The fiber have a 60μm diameter hollow air hole centrally, a 125μm diameter cladding, two 7.2μm /3.0μm (major axis/minor axis) elliptical cores, and a 3μm thickness silica cladding between core layer and air hole. The EECHF has a great potential for PMFs, high sensitivity in-fiber interferometers, poling fiber and Bio-sensor based on evanescent wave field. The fabrication technology is simple and versatile, and can be easily utilized to fabricate multi-core fiber with any desired aspect ratio elliptical core.

We demonstrate a compact fiber Michelson interferometer for refractive index (RI) sensing which is composed of an asymmetrical twin-core fiber (TCF) with a central core and a side core. By chemical etching a segment of the TCF to make the side core is nearly exposed, the effective RI of the side core mode is sensitive to the RI change of the external medium. Therefore, the optical path length difference between the central and side cores will vary with the ambient refractive index, which leads to a shift of the transmission spectrum of the Michelson interferometer. The experimental results show that the device has a refractive index resolution of ~10^-5 in the range of 1.34-1.38.

We design and fabricate an endoscope scanning fiber probe based on the piezoelectric transducer (PZT) for optical coherence tomography (OCT) to perform two-dimensional scanning. The driving part of the optical fiber probe is composed of two piezoelectric ceramics and a thin conductive substrate. The optical fiber is fixed in the middle of the piezoelectric ceramics to form a configuration of cantilever. A sine wave is employed for driving the PZT to make the cantilever vibrate along the vertical direction and form a line scanning. A saw tooth wave is load on the PZT to make the cantilever vibrate along the horizontal direction and form the field scanning. The frequency of the sine wave is set to be close to the resonance frequency of the fiber cantilever to increase the scanning range, whereas the frequency of the saw tooth wave is much lower than the resonance frequency to avoid the generation of blind spots. The finite element model is established for the theorical analysis of the device. Experimental results show that the scanning range can reach to 500x500 μm, and the scanning range can be adjusted by changing the amplitude of the drive signals.

A fiber-optic evanescent wave (EW) fluorescence sensor is often selected for its excellent performance, to detect the surface-specific event that takes place within a wavelength thickness of the immediate surface layer of the fiber core outside. In this paper, we describe a specific fiber-optic EW fluorescence sensor with a naturally built-in high signal to noise ratio, including a novel sensing architecture. It includes two identical, low hydroxyl content, large core, multimode plastic-clad silica fibers that are set perpendicular to one another, with a fiber for delivering incident exciting light and the other for receiving fluorescent light. An assay on the fiber-optic fluorescence sensor capable of simultaneously enhancing fluorescent signal and eliminating stray excitation light was examined. Such a capability can be achieved by reshaping a fluorescent sample fluid droplet and regulating the distance between the light exit of incident fiber and the bare core segment of receiving fiber. The prime significance of this work lies in its revelation of the outstanding influence of end-face total internal reflection (end-face-TIR) on enhancing signal intensity of fiber-optic EW fluorescence sensor, which reroutes the trajectories of the end-face-TIR capable rays and causes some of them to be detectable at the receiving end.

In this paper, a bending sensor based on distributed Bragg reflector (DBR) fiber laser with single longitudinal mode operation is presented and experimentally demonstrated. The single longitudinal mode has two split orthogonal polarization modes, introducing the intracavity birefringence and hence causing the emergence of frequency beat. Based on the bending induced birefringence, this laser can be used for curvature sensing by measurement of the beat frequency shift of polarization mode. The sensing characteristics of the laser were shown in detail through theoretical analysis and experimental verification.

A distributed temperature sensor (DTS) system with a sensing distance of 4 km was developed for applications in tunnel temperature measurement and fire alarm. Characteristics of DTS and experiment results are introduced. The results show that DTS system can play an important role in tunnel fire alarm.

To acquire the tension of the cable body, a novel measuring method with embedded FBG strain sensor in anchor zone is proposed. This paper describes the design details of the embedded FBG sensor. Based on the analysis of bridge anchor zone, crucial requirements of this sensor are known as package layer structure and the elasticity modulus of the package layer. And the epoxy with micro silicon powder is used as the package layer. Tensile tests are conducted with the tensile testing machine. The result shows that the linearity of sensor is 0.99974, the sensitivity is 2.74pm/N, and the repeatability is excellent. Finally, the sensors are mounted into the cable anchor zone for cable tensile test. The sensor has advantages in linearity and repeatability.

A ladder topology network based on white light fiber-optic Mach-Zehnder interferometer is introduced by consideration of multiplexing capacity and coupler tailoring. We enhance the multiplexing capacity of the sensors network by using optimization method. The network consists of 7 branches sensing array linked by 3 couplers. We contrast two different cases, one we choose couplers with equal coupling ratio, and the other one with tailored coupling ratio. Practical setup is built up for demonstrating the theoretical analysis. The experimental results have a good agreement with the numerical simulation. The maximum number of the fiber-optic sensors is 8 with equal coupling ratio, and 10 with tailored coupling ratio. The return average signal intensities of each sensor are balanced when we use tailored couplers. Both theoretical and experimental results show that the multiplexing capacity of the sensing system has been improved.

Optical fiber composite power cable such as optical phase conductor (OPPC) is significant for the development of smart grid. This paper discusses the distributed cable condition monitoring techniques of the OPPC, which adopts embedded single-mode fiber as the sensing medium. By applying optical time domain reflection and laser Raman scattering, high-resolution spatial positioning and high-precision distributed temperature measurement is executed. And the OPPC cable condition parameters including temperature and its location, current carrying capacity, and location of fracture and loss can be monitored online. OPPC cable distributed condition monitoring experimental system is set up, and the main parts including pulsed fiber laser, weak Raman signal reception, high speed acquisition and cumulative average processing, temperature demodulation and current carrying capacity analysis are introduced. The distributed cable condition monitoring techniques of the OPPC is significant for power transmission management and security.

Pure silica core optical fiber is commonly used as the sensing fiber in Raman-backscatter distributed temperature sensors (DTS) in heavy oil thermal well. However the sensing signal collected from this type of fiber statistically belongs to nonstationary random process which cannot be effectively de-noised by simply applying conventional methods. To solve this problem, we develop a novel noise suppression algorithm by combining wavelet multi-scale analysis and moving grey model GM(1,1). The algorithm first applies wavelet de-noising in spatial domain of temperature profile to remove the high frequency noise, then uses moving GM(1,1) method to remove both high frequency and low frequency nonstationary noise in time domain. Autoregressive (AR) model and least square regression are used to optimize the forecasting parameters of GM(1,1). Finally the results of both domains are reconstructed to obtain the de-noised profile. Long-term field test was proposed on the Karamay oil field F11051 steam stimulation well, Xinjiang Province, China. Field test result shows that signal to noise ratio (SNR) is improved by 11dB using the algorithm.

The GPD (General Phase Diversity) wavefront sensor generalizes the classical PD (Phase Diversity) algorithm and has more extensive applications. To restore the phase from the output signal of the sensor, we first decompose the output signal by Zernike mode and then use SPGD (Stochastic Parallel Gradient Descent) to search the optimum solution. The performance of phase retrieval algorithm is analyzed through two different aberrated wavefronts. One is an initial shape of 32-element deformable mirror sampled by the interferometer; the other is generated through the method proposed by N. Roddier. Simulation results show the method we put forward can correctly retrieve the phase from the output signal of the GPD wavefront sensor for randomly generated distorted wavefronts and is highly adaptable to noise.

Surface plasmon resonance (SPR) sensor has been widely investigated as an exceedingly powerful tool for biological and chemical detection in the past decay. As an essential component of both academic and commercial laboratories, several methods have been employed to monitor the excitation of SPR by measuring the light reflected from the sensor interface including modulation of angle, wavelength, intensity, phase and polarization. Among these methods, angle modulation (AM) and wavelength modulation (WM) are the most widely adopted in practice. However, the normal sensors system of the angle modulation was built by two ratable stages with a flow cell attaching a prism, and the angle of incidence rottingθ, the angle of reflect rotting 2θ. The mechanical structure can only be used in the angle modulation SPR sensor. In the present study, a new SPR is designed by a mechanical structure which can transform freely from wavelength to angle modulation. The different concentration Ethanol solution is tested by this system, and the linear range is very well from the volume ratio 0% to 60%. The primary application is done in real time detection of human IgG and antibody interaction, and the experimental results indicate that the new SPR system can detect human antibody at low concentration 1x10^-11g/ml with highly sensitivity and flexibility. The new SPR system is of great importance for potentially practical application in biosensor and life science with the extended the functions of the conventional SPR sensor, and provides the real-time and in-situ detection of the biomolecules.

Fiber optic vector hydrophone gets the acoustic field pressure gradient information by finite difference approximation, smaller as the separation D between the two sensing elements in the same direction is, more accurately the acoustic field information can be obtained. Because the sensitivity of the hydrophone is proportional to the separation D, the reduction of D is limited by the sensing element's geometry and the sensitivity of the hydrophone. For one-dimensional fiber optic gradient hydrophone, D is less than λ/4 as the measurement error of pressure gradient is smaller than 1dB. To achieve more outputs, the hydrophone can be configured by two interferometers scheme, then the pressure in acoustic center of the hydrophone can be acquired by the arithmetic average of the two interferometers' output of pressure, thus λ/7 as the upper limit of D for pressure measurement error 1dB maximum should be obeyed. The sensitivity decreases as the frequence of sound going down when D value is confirmed, so the lower limit of frequency band is mainly determined by optical noise, its minimum detectable signal grows quickly as frequency decrease, hence, good noise cancellation in two interferometers scheme can great improve the low frequency detection.

It is known that the incorporation of a self-induced grating in a saturable absorber can be used to drive fiber ring lasers to single-mode operation with ultra-narrow linewidth output. However, ultra-narrow linewidth erbium-doped fiber ring lasers (EDFRLs) usually suffer inevitably environmental perturbations for the relatively long resonant cavity, which may deteriorate the single-mode stability and practical applications in optical coherence detection. In this paper, the singlemode stability of the EDFRL under low-frequency resonant cavity disturbances has been investigated experimentally, and the induced mode hops have been measured to demonstrate that the occurrence of mode hopping can be triggered regularly by stretching the cavity fiber. The phenomenon of induced mode hopping indicates that the self-induced grating can only dynamically adjust itself to small disturbances in the cavity parameters within a finite range.

Fiber Bragg grating hydrophones exhibit exceptional properties for acoustic detection, oil exploration and other applications have been induced widely attention following the maturity of fiber grating fabricate technology. As the basic key point of optical fiber hydrophone array, hydrophone design has been focused on by many countries over the past two decades. In this paper, we present a design of fiber Bragg hydrophone based on side-hole packaged to enhanced sensitivity and optimize its parameters through theoretical approach. In our theoretical analysis, the radial and axial strain induced grating length changes are taken into account. The results show that the material parameters such as Possion ratio and Young's modules and structural parameters like the position, diameter, ellipticity and number of the side-hole have significant effects on the sensitivity of the hydrophone. By optimizing these parameters, a high sensitivity can be achieved. This hydrophone is fabricated and experienced hydrostatic and dynamic sound pressure test. The experimental results are in good agreement with the theoretical results.

Alkali atomic magnetometer is a good choice for magnetic testing devices with very-high sensitivity. Many parameters could affect the sensitivity of the atomic magnetometer. In this paper we described a Cs atomic magnetometer operating at normal temperature. A circularly polarized pumping light is used to polarize Cs atoms, while a linear polarized probing light is used to test the magneto-caused polarization rotation. During the experiment, we found the temperature is a very important parameter for the signal-to-noise ratio(SNR) enhancement. On the one hand, the higher temperature makes the SNR higher, which is good for sensitivity. On the other hand, the higher temperature causes more frequent collisions between the Cs atoms and the Cs atom and container wall, so that the polarization is easy to be broken, which reduces its sensitivity. So there must be a proper temperature for the high-sensitivity atomic magnetometer. We measured the magnetometer linewidth and sensitivity in the experiment. At optimum temperature the magnetometer achieves magnetic field sensitivity of 3.2pT/Hz^1/2.

The near-infrared spectrum is very practical for real-time analyzing in the field of industry. This paper describes the structure of optical system, which is a part of the well logging instruments. The optical system is designed to analyze the composition of underground fluid, using the differences between oil and water in near-infrared absorption. Using Beer- Lambert law, the article analyzes the light intensity when broad-spectrum light passes through the liquid. According to the results of analysis, a group of wavelength including center wavelength and bandwidth can be selected. With each selected wavelength, light intensity changes significantly as the concentration of liquid changes. By measuring the light intensity, the system can analyse the composition of underground fluid.

A fiber-Bragg-grating sensor interrogation system using a in-fiber Fabry-Pérot interferometer (IFFPI) is presented. The IFFPI was formed by splicing together a conventional single-mode fiber and a photonic crystal fiber with simple arcdischarge technique. The ellipsoidal air-cavity between the two fibers forms Fabry-Pérot cavity. The diffraction loss can be very low due to the focusing of reentrant and very short cavity length, thus resulting in high visibility and long period. The IFFPI is used as the filter component of the interrogation system. The resolving wavelength can achieve 2pm by using an Er-doped ring FBG laser in the experimental system. The advantages of this system are an all-fiber design, temperature insensitivity, quasistatic and dynamic operation, potential high speed and large range demodulation.

A miniature fiber optic pressure sensor based on Fabry-Perot interference fabricated on the tip of a single mode (SM) fiber is presented. The sensor measures only 125μm in diameter. A Fabry-Perot cavity and a thin silica diaphragm are fabricated by simple techniques involving only cleaving, wet chemical etching and fusion splicing. Interference pattern of the sensor is analyzed and issues in sensor design are discussed. The overall chemical reaction of the fiber wet etching is specifically represented. Pressure testing system is carried out. By tracing a peak point in the interference spectrum, the gap length of the sensor can be demodulated. Experimental results show the sensor has a good linearity. The sensor is made entirely of fused silica, whose structure has good stability, cabinet, simple for fabrication and low cost.

Based on the bending loss theory of polymer optical fiber, mathematical model of polymer optical fiber large strain sensing is established. Three different polymer optical fiber large strain sensitive structures are designed. And a corresponding intensity modulated polymer optical fiber large strain sensing system is established. The different aspects of properties of three designed sensitive structures are researched and compared by the means of ANSYS software simulation and experimental system. Experimental results show that the designed sensor of b-type structure is a large strain sensor, which has good performance. The b-type sensor's strain measurement range has up to 20%, moreover, its non-linear error is approximate 1.4%, and the system has advantages of high sensitivity.

A fiber Mach-Zehnder interferometer (MZI) constructed by concatenating a micro cavity in the fiber core and a taper is proposed and applied for temperature sensing. Femtosecond laser micro-machining technique and fusion splicing technique are utilized to fabricate the micro cavity in a single mode optical fiber core. The fiber taper is fabricated by electric arc-discharge with a conventional fusion splicer. A sensitivity of 68 pm/°C is obtained at the temperature range of 200-400°C. The interferometer is also characterized by different strain.It exhibits very low strain sensitivity because only low order cladding modes are excited by the micro cavity, which is a desirable merit for temperature sensor to eliminate cross sensitivity to strain.