This PDF file contains the front matter associated with SPIE Proceedings Volume 8561, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

For the purpose of investigating possibilities of utilizing changes of speckle patterns, to be observed in an output light spot from an optical fiber, due to external disturbance for sensing application, a certain load was applied onto an optical fiber through which laser beams emitted from a laser diode were propagating, and the resultant changes in the speckle patterns were observed. The obtained results showed that when the load was applied onto the optical fiber via a flat plate placed over the fiber, no significant changes were recognized in the speckle pattern. However, in the case where the optical fiber was placed so that corrugated bending of the fiber was induced by the load application via ridges, the number of speckles in the pattern decreased upon load application. Influences of a contact area size between the ridges and the optical fiber were also confirmed by employing several different arrangements for the load application. From these results, it was confirmed that observation of speckle patterns in an output light spot from an optical fiber can be utilized to realize sensing of load application onto the optical fiber by employing arrangements with ridges of suitable dimensions alternately disposed against the optical fiber to enhance effects of load application.

A systematic study of rock mass acoustic emission (AE) detection using distributed feedback (DFB) fiber grating lasers is presented. In this, a minimum detectable strain of 10^-12 is achieved in the experiment when using a fiber optic interferometric demodulation. The dynamic strain sensitivity of DFB fiber grating laser in different coupled modes is calibrated by a comparison with PZT AE sensor.. The acoustic emission directional characteristics of the DFB fiber grating laser are investigated by two kinds of analyzing method. In the first experiment, the relationship between the wavelength drift and the angle of a continuous acoustic emission source is determined. In the second experiment, the relationship between the percentage of wavelet packet energy and the angle of the impact response is established. Their acoustic emission directional characteristics make them suitable for determining principal strains and the direction of propagation of acoustic waves. Because of these advantages, the DFB fiber lasers will provide a practical and advanced measurement means in large civil structural health monitoring.

When coherent light beams, i.e., laser beams, are incident on one end of an optical fiber and transmitted to another end to exit from there so as to form an output light spot on a screen, non-uniform intensity distribution called a speckle pattern is often recognized in the output light spot. The authors confirmed that when a multimode optical bare fiber is placed in a loop onto a support plate, the speckle pattern in the output light spot appears to rotate while rotating or tilting the support plate. When an optical fiber is placed in a U-shape, instead of a loop, onto the support plate, the similar rotation of speckle pattern can also be observed. It was further confirmed that a distance between the optical fiber placed in parallel at the edge of the support plate provides certain influences on the observed rotating characteristics of the speckle pattern. The pattern rotation seems to be caused by upward and downward displacements of the optical fiber at the edge of the support plate. In addition, even in the case where a jacket-covered and connector-attached optical fiber is placed in the U-shape on the support plate and a laser diode is employed as a light source, similar speckle pattern rotation can be recognized. Such rotation phenomena of speckle patterns are observed with relatively good reproducibility, and therefore, there is a possibility of employing these phenomena for sensing purpose.

Temperature stability is one of the major obstacles that prevent the application of optical current sensors (OCSs) in the power industry. A simple yet effective method using thermoelectric effect and software packages to compensate for temperature drift of an OCS based on the Faraday effect is reported. A self-excited thermoelectric component is used to monitor the temperature of the Faraday element. The resolution of 1°C in temperature range from -40 to 80°C can be achieved. Combining accurate temperature information with software, the OCS with improved temperature stability has been demonstrated.

A high performance four-element DFB fiber laser hydrophone array system has been developed and tested. The system has the advantages of low noise floor (<10-6pm/√Hz @ 1 kHz) and wide bandwidth. Acoustic pressure sensitivity of DFB fiber laser hydrophone is 115±3dB re. Hz/Pa. Unbalanced Michelson interferometer and digital phase-generated carrier (PGC) demodulation are adopted to realize high resolution fiber laser wavelength shift demodulation. Four-element DFB fiber laser hydrophone array system performance is tested and its noise equivalent pressure (NEP) is below sea state zero (SS0). The theory analysis, design, development and test of the system are demonstrated in detail.

In this paper, we propose a nonlinear single-mode fiber FP cavity, in which CRDS is researched theoretically, and the relationship expression between output electric field amplitude and nonlinear phase shift is derived. Numerical results demonstrate that the output performance of nonlinear single-mode fiber Fabry–Perot cavity includes three phases: build-up, stability, and ring-down phase, output power is inversely proportional to the power in the cavity, when the power in cavity is larger than 2W, the stable time for output signal with instability becomes longer, but the effect of self-phase modulation on CRD time is ignoring.

We propose a new design of Mach-Zehnder interferometers (MZI) structure assembled with two arms composed of 400nm-diameter-hole-modified silica photonic crystal fibers (PCFs) and immersed in solvent solution. The proposed design is found to enhance considerably the sensitivity. A highly-sensitive versatile interferometry technique is used to determine the phase shift from both arms and consequently the specimen’s information can be retrieved. The proposed sensor was first tested when considering the specimen to be analyzed with different concentrations for a probing light of 325 nm. The sensitivity of detecting the benzene solutions in water reaches 9 rad/μm which is much higher compared to what was achieved in photonic nanowires. Then, the detection of corn oil into olive oil is achieved with high sensitivity of 14.7 rad/μm demonstrating that the sensor is capable of detecting a RI variation of 4×10^-7 in only 1-mm sensitive area- length. Thus, the proposed MZI-based PCF-sensor shows to be very attractive for compact, flexible and high sensitive biochemical sensing.

In this work, we present the optical characterization of a two-dimensional (2D) L3 photonic crystal (PhC) cavity biosensor in visible region by using 3D Finite Difference Time Domain (FDTD) method. The sensor is based on GaN material and integrated with a microfluidic channel. Sensing is performed by measuring the wavelength shift of the PhC cavity resonant peak, whose spectral position is sensitive to refractive index changes of dielectric material inside microfluidic channel. We simulate the PhC cavity with water (n=1.33) and two immersion oils (n=1.48 and n=1.518) overlaid. Spectral peak width was found to be 9.8nm around 650nm. A spectral shift of peak wavelength with index change of 35nm/RIU was observed. Measured peak shift (Δλ = 6.5nm) corresponds to a detectable index change Δn = 0.188.

We develop coupled-mode formulism for multimode couplings of LP₀₁ core modes to LP_1n cladding modes in singlehelix chiral long-period fiber gratings (S-CLPG). Then mode-coupling characteristics of the structure, such as coupling coefficients and relative bandwidths of dips are studied and compared with those of the conventional long-period fiber grating (LPG). Subsequently, transmission spectral characteristics in response to the liquid level are investigated for SCLPG partially immersing in a liquid with refractive index lower than that of the fiber cladding. Simulation results indicate that the dips corresponding to the multimode couplings in the transmission spectrum will shift continuously and monotonically as liquid level changes. Thus S-CLPG could be used for liquid level sensing based on wavelength interrogation, which is beneficial to avoid sensitivity deterioration caused by power instability in power interrogation for most conventional LPG-based liquid level sensors. In addition, we identify that the sensitivity can be enhanced with a thinner fiber cladding or by utilizing higher-order cladding mode resonance. The optimization result indicates that the wavelength shift will be over 1.03 nm per millimeter liquid level change.

A fiber-optic flexural disk microphone is developed to detect acoustic signals in the air. It consists of a Mach-Zehnder interferometer with an optimized sensing arm of 7.93 m. The disk’s resonance frequencies and their influence on the microphone’s sensitivity are investigated. The microphone’s frequency response is measured in the frequency range from 100 Hz to 5 kHz and the average phase sensitivity is about -120.7 dB re 1rad/μPa.

This is the study of relation between thermal and magnetic properties of permanent magnets. The concept of adiabatic demagnetization gives the basic idea on variation in temperature of paramagnetic substances due to the application of magnetic field. With the understanding of adiabatic demagnetization the variations in temperature of ferromagnetic materials can be explained. In both cases, adiabatic demagnetization tells us about conservation of energy. The study on thermal properties of ferromagnetic materials at cryogenic temperatures gives the amount of thermal energy being transferred from or to the surroundings and hence gives the variations in magnetic fields due to temperature changes. As samarium cobalt rare earth permanent magnet do quite well at cryogenic temperatures, this study is much useful in future applications of permanent magnets in space for a renewable energy source. This will enable us to look into the design and working of a device that can convert thermal energy to mechanical energy which leads to thinking of energy conversion without causing harm to our environment. Numerous research works report the successful use of samarium cobalt to temperatures as low as 2 K.

Landslide is typical geo-hazards which causes serious threat to the human lives and infrastructures. It's necessary to develop a monitoring system to avoid landslide disasters. In this paper, a real time monitoring system based on optical fiber sensing technology was designed to monitor the health status of slope. Three types of optical fiber sensors, including FBG strain gauge embedded in anchor, FBG inclinometer, and FBG soil-pressure sensor, were demonstrated. A light switch was introduced to expand the demodulation equipment to 16 channels, which enlarges the capacity of more than 200 FBG sensors. This remote and real-time monitoring system can be used not only for landslide monitoring but also for large scale structure health monitoring.

We demonstrated experimentally the fabrication of tilted long-period fiber gratings (TLPFGs) with by CO₂ laser. The writing efficiency can be dramatically improved by increasing the tilt angle. We fabricated the non-titled long-period fiber gratings with equivalent grating period in the same fiber. The experimental results show that the transmission spectra of non-titled equivalent LPFGs are similar with that of the TLPFGs. The TLPFG is found to have higher refractive index sensitivity than the corresponding equivalent LPFG.

We propose a way to enhance the temperature sensitivity of single-mode-multimode-single-mode (SMS) fiber structure, by replacing the cladding of silica multimode fiber with a polymer coating. Based on the mode expansion method, we analyze transmission characteristics of the polymer-coated SMS fiber structure and optimize design parameters for sensing. Then we do experiments and verify theoretical analysis. By using the optimized parameters in sample fabrication, a temperature sensor is obtained with an easily detected and demodulated transmission spectrum; and then by monitoring valley wavelength shifts, a measuring sensitivity of about 706 pm/°C is achieved.

An Arc Discharge Erasing (ADE) technique was proposed to erase the refractive index modulation at selective area in Fiber Bragg Gratings (FBGs) and was taken to fabricate Phase Shift FBGs (PSFBGs). The ADE effect and the PSFBGs fabrication technology was demonstrated experimentally first. The capability and fabrication technique was investigated and the full control of the transmission spectral characteristics of PSFBGs, including the peak wavelength position, intensity and bandwidth, was demonstrated. To get optimum technique parameters, the experimental studies were done under different discharge electric current, time and position, and the effect of annealing processing were investigated experimentally too. With this technique, an in-line distributed feedback fiber laser with 1.16 kHz line-width was made.

We characterized the temperature sensitivity of birefringence of typical solid core polarization maintaining photonic crystal fiber (PM-PCF). Mainly the temperature dependence of birefringence is determined by two factors which are thermo-optic effects and thermal expansion. Numerical simulation with ANSYS and RSOFT show that the birefringence temperature susceptibility can be described as a polynomial function of Λ (distance between small holes) and zero temperature coefficient may be obtained at optimum Λ. A high precision birefringence measure setup was built and the birefringence of five PM-PCFs samples with different Λ were measured under different temperature. The experimental result agreed well with the simulation.

A novel optical voltage sensor is proposed and experimentally demonstrated by use of single Fresnel rhomb bismuth germanate crystal. Different from previous polarimetric voltage sensors, the proposed voltage sensor can provide the π/2 optical bias by two times of total internal reflection of light wave in the crystal, thus any additional quarter wave plate is not necessary. In principle, the influences of measurand voltage and temperature on the π/2 optical bias are neglectable. The 50Hz ac voltage in the range of 2~2000V is measured with good linearity.

The spectrum of Gauss apodized fiber Bragg grating (FBG) is analyzed by using transfer matrix method, and the basic principles of sub-pixel curve fitting algorithms including mass center, Gauss and full-width-at-half-maximum (FWHM) are discussed. Based on this, simulation and experimental results are given to compare the three curve fitting algorithms. The results reveal that in simulation, mass center fitting method with an accuracy of 13pm while in experiment, FWHM fitting method with an accuracy of 23pm provides a better match to the actual curve. The research achievements have been applied on the prototype of linear-array detector grating spectrometer and have potential market in portable FBG interrogation field.

Fiber inhomogeneity induced random birefringence in single mode fiber (SMF) can lead to the polarization fading effect in distributed fiber vibration sensor using Mach-Zehnder interferometry. By considering the contributions of both visibility and phase noises in interference output signal, the influence of polarization fading effect on the position accuracy of distributed vibration sensor using cross-correlation algorithm is theoretically derived. A new term of equivalent signal to noise ratio (SNR_e) is defined in the model. Based on the theory, a novel method for decreasing the positioning error of low-frequency vibration signal is given and verified by field test results.

We present a numerical study of the sensitivity of guided modes due to the presence of small mechanical vibrations. Analysis is performed utilising finite elements method (FEM) with help of both 2D and 3D models, where changes to the field distributions associated with the guided modes are computed in order to read the position of a conducting plate suspended over a waveguide. The sensitivity related to the guided modes is analysed and a possibility to improve the sensitivity by combining the sensing effect of several modes is investigated. By utilizing FEM, the optical response to the system is studied in terms of both indiviudal response to the perturbation and the collective response by using the concept of multimode interference (MMI). The preliminary models predict a theoretical sensitivity limit of 2:4 %/nm in terms of normalised power transmission for a MMI of only 4:1 μm length.

Due to their small footprint and high sensitivity to biological molecule binding, planar optical microring resonators gained high interest for use as optical biosensors. Typically, microring resonators are made of semiconductor based materials, and are manufactured by time-consuming lithography and etching steps. Semiconductor based waveguides have high refractive indices, and thus, a high refractive index contrast between core and cladding. In this case, due to strong mode confinement, bending loss is a comparably minor issue and becomes relevant only at small bending radii of less than 5 μm. The main loss is determined by surface scattering, and thus, semiconductor based curved waveguides need to be designed and manufactured to have very smooth sidewalls. If polymer materials are used, microring resonators can be cost-efficiently manufactured by nanoimprint lithography. The resulting larger polymer waveguide dimensions facilitate in- and out-coupling, and polymer surfaces allow using established surface biofunctionalization techniques. For polymer waveguides, due to the small refractive index contrast, surface scattering loss is a minor issue, but bending loss becomes dominant for radii of less than 80 μm due to the low mode confinement to the core. In this work, design guidelines for polymer microring resonator waveguides are given and compared to semiconductor based waveguides. Waveguide losses due to bending and surface roughness are determined analytically or numerically by finite element methods. Coupling coefficients are calculated by finite element methods and coupled-mode theory. Resulting conclusions for designing polymer waveguides and semiconductor waveguides are derived.

In the field of vision measuring, camera calibration is a necessary precondition of the three-dimensional measurements. For the sake of obtaining high-precision external parameters, the inadequacies which cycling conditions restrict external parameters calculation in traditional calibration method was founded and elaborated in detail. The re-projection error was re-selected as cycling conditions and a new amended method was designed to solve the above shortcomings. Then Binocular vision system calibration experiments was carried , it has been found that standard deviation and the maximum error of three-dimensional reconstruction target after the amendments for external parameters is less than the calibration errors before the amendments.

A novel detection and analysis platform which is based on two-electrode electrochemical voltammetry system has been developed for multi-parameter measurement of drinking water. There are three unit in this platform, multi-sensor unit, hardware system unit and control and processing software unit. After choosing detection objects on computer, the control and processing software unit can control the hardware system unit apply corresponding potential on appropriate working electrode automatically. Currents can be collected on counter electrode and sent to computer for data processing. The multi-sensor unit contains Ag, Pt, Au, etc. noble metal electrodes as working electrodes and a large area ringlike stainless steel was as counter electrode. Comparing with conventional three-electrode voltammetry system, reference electrode has been eliminated in this platform by mechanical improvement of sensor array. This platform has been employed on detection of two common parameters in drinking water, electric conductivity (EC) and concentrations of heavy metal ions. In EC measurement, bipolar pulse with high frequency has been applied on Pt working electrode. In heavy metal ion of lead detection, staircase wave stripping voltammetry was applied on Ag working electrode. This detection platform owns high mechanical strength sensor, low maintenance requirements and easy to use, it could be used for drinking water quality monitoring in laboratory or industry locale.

In this paper, the characteristics of the high birefringence fiber (HBF) strain sensor based on piezoelectric ceramic have researched, and analyzed with the force of piezoelectric ceramic because the voltage applied on HBF and the force of the HBF wounded on the piezoelectric ceramic. We can get the relationship between the applied voltage and the shift of the trough wavelength by calculating the equation of the shift of birefringence and trough wavelength, at the same time, compared the experimental with fitting curves and the difference between elliptical fiber and panda fiber. Then connect the fiber sensing experiment based on the piezoelectric ceramic with the fiber temperature sensing experiment, and change the temperature and the stress individually. Lastly analyze the results of the joint experiments.

This article analyses the motion detection results based on the Joint Transformer Correlator, and discusses the effect of shape, brightness and SNR of the correlation peak on the accuracy of results. The experiment shows that the shape of the correlation peak has more significant impact the motion detection than other factors, and the laser power level was relevant to shape, brightness and SNR of the correlation peak: the laser power level of input-image influences the graph of power spectrum, and changes the last shape and brightness of correlation peak image; the laser power level of the output-power spectrum affects the collected correlation pattern, and alters the shape and SNR of the correlation peak image. An optimal laser power of output power spectrum is found corresponding to a particular laser power of input image. In this paper, the correlation peak image quality evaluation function model is proposed and its effectiveness is verified by experiment data.

High nitrogen fertilizer input is the main manner to maintain the high-yield crops in farmland in China. The average application quantity of nitrogen fertilizer in China is significantly higher than some developed countries in the world. However, the nitrogen fertilizer utilization efficiency is very low. Thus, high sensitivity sensing and on-line monitoring ammonia concentration were needed to quickly acquire the soil nutrient information and to get the nitrogen fertilizer utilization efficiency. A high sensitivity ammonia concentration sensor used in farmland has been developed based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, high frequency modulation technique and long optical path technique. TDLAS is a method to obtain the spectroscopy of gas molecule single absorption line in the characteristic absorption spectrum region as the characteristic of the distributed feed back (DFB) laser with narrow line width and tunability. A sensor array formed with three ammonia concentration sensors by distributed sensing technique was used for ammonia volatilization experiment in a wide range of farmland. It was verified that the performance consistency of the three ammonia sensors was good and the sensor array realized the regional ammonia concentration monitoring. Continuous measurement results showed that the ammonia concentration influenced by the volatile source location, wind direction, weather and other factors, and it was positively correlated with the ammonia volatilization rate. The ammonia sensor array is suitable for continuously ammonia volatilization monitoring in a wide range of farmland environment with its high sensitivity, rapid response time without gas sampling.

In this paper, we develop a new Medium Access Control (MAC) protocol that based on hybrid FDMA/TDMA technology with three-jump network. This protocol combines the advantages of both FDMA and TDMA. The communication of cluster heads is based on FDMA technology which can decrease the crosstalk between different frequency and the cluster heads can identify each other easily; the inter cluster communication is based on TDMA technology to achieve basic time synchronization. Then the time synchronization of the network was obtained. At the same time, the three-jump network increased the range of communication system and reduced the power. The protocol adopts cluster head rotation mechanism. TH-MAC has the advantages of low crosstalk between frequency, low power and low latency. It applies to the large-scale collection of data and information about industry and agriculture and worth of application.

In this paper, a pressure sensor based on high-birefringence fiber loop mirror (HiBi-FLM) is proposed and demonstrated. The high-birefringence fiber is pasted to an inflated, elastic, ring shaped rubber gasbag and served as a sensitive probe. When outside pressure changes, the volume of the gas in the ring rubber gasbag changes and it makes the strength of the high-birefringence fiber variety. The relationship between shift of the resonant wavelength (peak wavelength) and pressure is discussed and experimentally researched. Experimental results show that the sensitivity is 1.63×10^-3nm/Pa. The sensor has many advantages such as high sensitivity, polarization independent, easy manufacture, low cost.

A novel surface plasmon resonance (SPR) sensor based on the multihole optical fiber with TiO₂ layer is proposed and numerically characterized. The finite element method(FEM) is used to analyze the characteristics of the SPR sensor. The effects of the pitch between air holes, the thicknesses of the gold film and titanium dioxide layer on the sensor characteristics are investigated, and the sensitivity of proposed sensor is also given. The results indicate that when the thickness of gold film increases, the resonance wavelength shifts to longer wavelength, and the resonance peak broadens. The spectral tuning of the plasmon resonance can be more efficiently realized by changing the TiO₂ layer thickness. The maximal refractive-index resolution of the proposed sensor for aqueous analytes is 5×10^-5.

To achieve pH detection of multi-points, a new pH sensor based on pH sensitive hydrogel swelling detection by a fiber Bragg grating is proposed. The deflection of a silica membrane due to pH value change induced hydrogel swelling is measured by the center wavelength shifts of a fiber Bragg grating epoxied on the membrane. The relation between center wavelength shifts of the fiber Bragg grating with the hydrogel swelling behavior was studied experimentally. Around 100pm shift of the fiber Bragg grating center wavelength was observed when the pH value was changed from 4 to 7 or from 7 to 10 by using pH standard solutions, which fundamentally proved the feasibility of this method for pH detection.

A CO₂-induced LPG with an over-coupled resonant dip is fabricated. The bending characteristics of proposed LPG are experimentally studied in detail. The results show that the spacing between the two resonant wavelengths has a periodic behavior along circular directions. The spacing between the two resonant wavelengths changes nearly linearly against the curvature under certain bending directions. The bend sensitivities under two bending directions are 7.19nm/m and 3.13nm/m, respectively. In addition, the over-coupled dip splits into two dips when increases curvature under a special bending direction, which may be attributed to that new cladding mode meet coupling condition is excited.

A novel all-metal fiber-optic accelerometer with Michelson interferometric configuration is proposed, using mass blocks and flexible reed structure. The sensing arm is configured to directly transform the applied acceleration to fiber deformation in axial direction, which increases the acceleration sensitivity of the sensor. The axis of the reference arm is set orthogonal to that of the sensing arm in order to make it insensitive to applied acceleration, and thus decrease the phase noise of the sensor. Using the flexible reed of 1mm thick and the mass block of 208g, an acceleration sensitivity of 556.7rad/g(54.9dB) is achieved by this structure. In the case of 10^-4 rad/rt Hz(100Hz)noise floor, the minimum detectable acceleration is 200ng/rt Hz.

As a new area of research, Wireless Sensors Network (WSN) has played a significant role in regional information monitoring area for its potential practical value. However, the promotion of WSN has been limited because of its short lifetime. In a traditional multi-hop WSN, the nodes close to the static Sink easily suffer the energy failure for transmitting large amounts of extra data. This leads to an “energy hole” phenomenon in WSN and finally causes the early death of the whole network. To solve this problem, a mobile Sink was brought in to balance the energy consumption of the whole network. This Mobile Sink Wireless Sensors Network (MSWSN) has recently received a lot of attention from the research community. Based on this view, the paper presents a design proposal of a mobile Sink used in regional monitoring area. To achieve the design requirement, the hardware platform is designed based on a LM4F232H5QD ARM Cortex-M4F processor and the driver program and applications are designed based on embedded real time operation system μC/OS-III. This mobile Sink could not only transmit data, but also calculate its location and reveal the information on OLED. Compared with traditional WSN, MSWSN shows appealing characteristics of providing longer network lifetimes and the flexibility to adapt dissemination strategies according to applications’ requirements and has proved to be more efficient.

The Sagnac loop mirror of high birefringence fiber is developing greater more than other fiber because it has the advantages of high precision, wide spectrum and simple structure in applications. In this paper, general theory of Sagnac loop mirror of high birefringence fiber is presented. Since Sagnac loop mirror of high birefringence fiber is more sensitive to its environmental temperature, an intelligent temperature measurement system based on Sagnac loop mirror of high birefringence fiber is designed. A 1550nm-laser is used as source light going through the high birefringence fiber Sagnac loop mirror. The amplitude of output beam is converted into electrical signals with Photo-Diode (PD), and the signal is collected by the MCU(Microcontroller Unit) to complete the analog-digital conversion. After calibration, the temperature is calculated, and then shown on LCD displayer. Various parts of the electronic measurement system are introduced in details, containing MCU C8051F020 with microcontroller, its internal AD-convert, calibration program and measurement program of temperature.The fiber optic temperature measurement system is compact, solid with good portability, as well as independent real-time analysis of data processing capability. It’s provides a good preliminary basis for implementation the new fiber-optic temperature measurement system. And this system has broad application prospects of a good practice. The arrangement of temperature measurement is from 30°C to 50°C with accuracy ±0.2°C in recent research experiment.

We have developed an observable sensitive fiber nonlinear polarization sensing method based on the whispering gallery mode (WGM). The spectral position of the WGM excited by evanescence field shifts in response to the refractive index change of the fiber’s dielectric caused by nonlinear polarization interaction with incident light field or surrounded electromagnetic filed. Theoretical resonance spectral shift equation was derived and calculation showed that a sensitivity of approximately 0.0172∼0.0196 RIU (refractive index unit) per nm at least was achieved due to the extremely high Q factor associated with the WGM.

A humidity sensor is proposed for detecting air moisture content based on tapered optical fiber. According to optical energy transmission theory, geometrical optics, the sensing mechanism of humidity sensor is described by analyzing the evanescent field around the sensing fiber. The relationships between the dimensions and spectral characteristics of the taper have been analyzed, respectively. The results show that the taper shape is important for designing a humidity sensor. The experimental curves can be obtained by comparing the transimission loss and humidity, and the errors are also given. The humidity is analyzed in different air moisture content. The humidity measurement resolution is 1% as the measuring range varies within 50~95%. The transmision loss decreases as increasing humidity. Thus, the high dynamic performance can allows this sensor to be used for humidity monitoring in time.

Light curtain systems are used to detect intruders in various cases and places. However, it is necessary to adjust the position of the light detecting element accurately in order to receive the irradiating laser light. We propose a new type safety light curtain system that uses a hemispherical mirror and an LED in this research. A hemispherical mirror can reflect irradiating light rays surroundings of 180° in the vertical direction and 360° in the horizontal direction. When an LED is at a position that is higher than the hemispherical mirror, the LED irradiating light can be reflected by the hemispherical mirror, even if the LED is arbitrarily set up. In the case that, the light of LED is intercepted when an intruder passes between the LED and the hemispherical mirror, the output voltage of the light detecting element decreases. We can set a proper threshold voltage value of the detecting element to judge whether an intruder passes or not. Our system uses a PSOC microcomputer to judge the output voltage of the receiving element with the threshold voltage value. In addition, the LED output light is modulated by 10kHz in order to avoid the influence of the surrounding turbulence light. Our experiment succeeded to detect intruder using the proposed system without accurate light axis setting.

A new Analog-Digital device is introduced in this paper, which is newly applied on the signal process circuit of the high resolution remote sensing charge-Coupled Device (CCD). Base on the signal process circuit, the new AD had two selectable operated mode which is CDS mode and S/H mode, the AD had LVDS transmission mode, the frequency of the data transmission reached to 320 Mhz. the AD’s registers was written in different operate mode and the main registers’ function was validated and introduced. The image was got by using this signal process system and was analyzed in the paper.

Helicopter stabilization-aiming system is librated strongly because of the strong libration resulted by the engine and airscrew during the helicopter flight, which affect seriously the viewing distance of the electro-optical system.a method of measuring dynamic MRTD of infrared imaging system is advanced in this paper, the experimental installation is designed and developed, The libration of helicopter stabilization and aiming system is simulated by experimentation, and in order to get the MRTD of infrared imaging system under libration, the experimental data is analyzed by image processing and statistical methods. Experimentation result shows that measurement of dynamic MRTD can be achieved commendably utilizing the advanced method and experimental facilities, which establishes basement for estimating the viewing distance effect from libration in the laboratory.

We propose a multiplexing bending sensor system based on a special double cladding fiber (DCF). Based on the filter characteristic of the DCF transmission spectrum and the narrow band of distributed feedback laser pulse, the intensity changes can indicate the variation of measurand. A sensing scheme with four sensor heads in parallel is investigated in experiment. The variation of sensors output was directly detected and the four channel sensing signals were separated by a certain optical path difference of the sensor heads. The experiment results show that the intensity of the sensing signals decreases monotonously with increasing the bending curvature radius. And we can get good performance between 0.0-1.8m^-1 of the curvature radius.

One type of single-photon detector that without cooler, which is mainly consisted by noise voltage control circuit and precise pulse width detection circuit, is presented. The noise voltage control circuit is using the characteristic the noise rapid increase in avalanche voltage. The detector signal after forward and video amplifier is measured. When noise voltage exceed a certain range, the bias voltage would be decreased; when noise signal minished, the bias voltage would be increased. So the bias voltage of APD is dynamically fixed by certain voltage. When the avalanche voltage changes with the temperature, the noise character nearby avalanche is resemble. So the bias voltage could be stabilized based on noise character. The detector’s output SNR would descend greatly if there was no cooler, and the phonon avalanche signal would not measured efficiently by the tradition extent detection. Considering the difference of time width between photon avalanche signal and noise signal, the precise pulse width detection method is adopted. It can filter the narrow noise signal and only detect photon avalanche signal which has larger pulse width efficiently.

We present an optical fiber sensing system for discrete multi-target’s on-off states detection and location. The sensing system consists of multiple cascaded 1x2 fiber couplers (FCs). Each FC is connected to a reflective optical switch sensor (ROSS). A ROSS is corresponding to a target to be detected. The system can remotely detect the on-off states of multiple ROSSs, as well as accurately and rapidly locate the ROSSs in alarm states. By detecting the various intensities of light pulses reflected by each ROSS, their on-off states can be monitored. The ROSSs in alarm states can be located by directly measuring the reflected light pulse intensity at corresponding time axis or the declined peaks of short-time crosscorrelation of reflection pulse train during adjacent optical pulse period in noisy case. The simulation results with the same and different ROSS intervals show that the detection and location methods proposed are feasible and effective. The system can be used to detect and locate different kinds of physical and chemical targets discretely distributed at the same time, which can prompt state changes of the ROSSs. Although the proposed system is similar to the optical time domain reflectometry (OTDR) in structure, it has better real time performance and lower cost than OTDR.

In this paper, effects of diameter on characteristics of a LPFG with numerical simulations adopting a three-layer model and experimental demonstrations are presented, including the normalized coupling coefficient, the effective refractive index, the resonant wavelength, the shape of the attenuation dip and the refractive index sensitivity. The couplings between the core mode and the EH cladding modes increase faster than that of the HE cladding modes as the fiber diameter decreases. Moreover, the depth and bandwidth of the attenuation dip vary faster in thinner fiber due to the increase of the coupling coefficient, comparing with LPFGs in common fiber. The resonant wavelengths of lower order cladding modes move mainly toward the shorter wavelength, while that of higher order cladding modes move mainly toward the longer wavelength as a function of the exponential shape as the fiber radius reducing and the external refractive index increasing. The refractive index sensitivity is greatly enhanced when reducing the fiber diameter and using the taper structure. Therefore, we can utilize the higher sensitivity of different cladding mode at a suitable wavelength by controlling the diameter of the fiber taper waist. Furthermore, the sensing resolution and the cladding mode can also be selected by controlling the fiber diameter, which can be greatly used in many fields.

A compact high-sensitivity distributed feedback (DFB) fiber laser strain sensor with length of only 56 mm is investigated. The intrinsic performances including optical efficiency and acoustic sensing characteristics of bare DFB fiber laser are tested before packaging. Then polyurethane cylinder and spindle structures are applied for fiber laser packaging. By use of a Mach-Zehnder interferometer and a standard optical phase demodulator, the frequency response of DFB fiber laser before and after packaging is tested in a vibration liquid sound field and compared to standard PZT hydrophone. The experimental results show that the prestress on bare fiber laser affects the frequency response rather than strain sensitivity; the frequency sensitivity of spindle structure packaged DFB fiber laser hydrophone is about 113dB•re•Hz•Pa^-1 at 1 kHz, which is 55 dB higher than bare fiber laser under the same prestress. It is remarkable that in a quite wide frequency range from 10 Hz to 10 kHz, it has a more flat frequency response with about ±8 dB fluctuation than that of cylinder structure packaged DFB FL.

We need high-pass filtering in interferometric fiber-optic hydrophone system. In this paper, two methods of zero-phase high-pass filtering are introduced. The two methods are based on infinite impulse response (IIR) filter and frequency filtering alternatively. They can both shorten the data processing time compared to finite impulse response (FIR) filter on the expense of memory cost, which is also discussed in this paper.

A design of semiconductor ice box is introduced in the paper, which is cooled by solar power supply. The box is constituted by four major parts. There are a solar power panel, a solar charge controller, a hermetic box and a series of semiconductor frigorific pieces. The solar power panel collects solar energy through the Photovoltaic effect. The solar energy is stored in storage battery after being regulated by the DC/DC converting circuit of the solar charge controller. The charge controller circuit contains over-charging circuit, over-discharging circuit, short circuit, overload circuit and reversed polarity protection circuit. The storage battery supplies power to the ice box. The solar charge controller can automatically track the maximum power point in terms of the solar intensity. The cooling system is made up of semiconductor frigorific pieces, whose power is exclusively provided by solar energy. The whole device is small and portable, and can be applied in some areas of environmental protection and energy saving.

In order to improve the resolution of laser Doppler interferometer, the noise of the system need to be suppressed. Through the analysis of the influence of laser relaxation oscillation mixing with signals in phase generated carrier (PGC) demodulation, we can get a conclusion that the low-frequency part of the laser intensity noise have a greater impact on the signal to noise ratio of PGC demodulation. By using Optoelectronic negative feedback method, we can achieve effective suppression of the low-frequency laser intensity noise and laser relaxation oscillation peak, which reduce the influence of the mixing of the light source intensity noise, and the system signal to noise ratio (SNR) is improved.

We present an in-fiber Mach-Zehnder type interferometer (MZI) in single mode fiber based on lateral offset splicing technique. The MZI relies on the interference between the fundamental core mode and a co-propagating cladding mode. To build an in-fiber MZI, we need one element or device which excites two co-propagating modes and another one to recombine them. In our case, the excitation and recombination of modes is realized by two cascaded lateral offset splicing joints. The effects of the lateral offset amount, the interferometer cavity length, and the fusion splicing parameters on the property and performance of the in-fiber MZI were investigated experimentally. By choosing an appropriate lateral offset amount, the MZIs with good interference fringe contrast and low insertion loss can be fabricated. Several in-fiber MZIs with different interferometer lengths were built and it is found that the interference peak wavelength spacing is inversely proportional to the interferometer length L. The potential applications of the proposed in-fiber MZI were further investigated as strain sensors.

Modal fields, propagation constant and power distribution of single-mode eccentric core optical fiber are calculated based on the weakly wave-guiding approximation. The calculation of the propagation constant and power distribution is in terms of the change of the coating refractive index and eccentric distance. It is found that the evanescent field power depends on the coating refractive index and eccentric distance. In eccentric core side coating, the higher coating refractive index, the stronger evanescent field power and the larger eccentric distance, the weaker evanescent field power. The present results will be useful for deciding the geometric structure of the fiber to achieve maximum power of the evanescent field in eccentric core side coating to enhance the sensing sensitivity.

A simple temperature sensor based on a bent singlemode–multimode–singlemode (SMS) fiber structure fastened on a polymer base plate is proposed and experimentally investigated. The surrounding refractive index (RI) is higher than that of the silica fiber and RI changes with temperature will not lead to wavelength shift. This SMS fiber structure utilizes changing of temperature to control the curvature of SMS fiber which is induced by expanding of polymer base plate. The shifts of central wavelength are measured at temperature range from 59 to 82 °C. The proposed temperature sensor offers sensitivity of 3.9 nm/°C, which is significantly higher than that of a normal straight SMS structure or a grating-based fiber structure.

Fiber Bragg grating sensors have been attracted more attention due to its excellent advantages, such as small size, light weight, low cost, immunity to electromagnetic interference, multiplexing and so on, which offer a widely application in optical sensing and communication field. Following the appearance of micro/nano-fiber (MNF), it is imperative to develop the manufactured technology of MNF devices, MNF Bragg gratings are the important passive device among these. In this paper, we simulate the effective refractive index in fiber core using two-layer model. Meanwhile, we present a new method to fabricate a 6μm diameter fiber Bragg grating through successive improvement of manufactured technology. The small cladding diameter fiber was obtained by immersing an optical photosensitive fiber in different concentrations of hydrofluoric acid solutions. Then a MNF is fabricated from the small cladding diameter fiber by drawing. Finally a 6μm-diameter fiber Bragg grating was written using phase mask technology with a higher reflection. The testing results of this grating showed a good agreement with the simulation.

This paper research an ultra long distance distributed fiber-optic intrusion detects system. Laser source is amplified and modulated before input to the dual Mach-Zehnder interferometers. This ensures the system can detect longer distance with less loss and nonlinearity than continuous laser input. The cross correlation algorithm is considered to locate the vibration event after the polarization controlled of the optical source, and the locate precision is also discussed. Finally, an experiment result is given as the sensing fiber length is 112km with the location precision about 160m.