This pdf file contains the Front Matter associated with SPIE Proceedings Volume 7853, including the Title page, Copyright information, Table of Contents, and Conference Committee listing.

Gas sensing is evolving into an important application contributing particularly to environmental and safety monitoring. Fibre optic sensing will have an important role to play as the need for gas measurements increase. This paper seeks to overview of the optical techniques which are compatible with fibre optic technology and present a limited snapshot of the applications. Fibre optic techniques offer intrinsic safety, reliability and very long interrogation distances over the fibre link together with prospects for highly multiplexed and distributed systems. There are two basic approaches for fibre sensing targeted at gas measurements. The first involves some intermediate compound in contact with the end of the fibre (or deposited along the fibre) whose optical properties change with the presence of the gas of interest, usually measured spectroscopically. The second involves direct absorption spectroscopy typically in the near infrared. Former techniques are invariably responsive to a number of gas species and are usually difficult to calibrate accurately. The latter techniques are highly gas specific and can be accurately calibrated. However both approaches have their application sectors depending upon particular measurement requirements. The paper presents a brief overview of the principles of both these techniques and analyses some of their applications.

We review recent advances in the plasmonic sensors associated with chemical and biological sensor system and introduce their structural design method for enhancement of sensing performance such as detection limits, sensitivity, and dynamic range, relative to the commercial systems. In addition, the effect of structural parameters of surface plasmon resonance based sensors with transmission or reflection-type configuration is discussed. We also discuss the optimal condition of the sensors with nano-structures as well as flat metallic layer structures for practical sensing and provide the methods for improving sensing capability.

A CCD fiber Bragg grating sensor demodulation system based on FPGA is proposed. The system is divided into three units: spectral imaging unit, signal detection unit and signal acquisition and processing unit. The spectral imaging unit uses reflective imaging system, which has few aberration, small size, simple structure and low cost. In the signal detection unit, information of spectrum are accessed by CCD detector, the measurement of spectral line is converted into the measurement of the pixel position of spot, multi point can be simultaneously measured, so the system's reusability, stability and reliability are improved. In the signal acquisition and processing unit, drive circuit and signal acquisition and processing circuit are designed by programmable logic device FPGA, fully use of programmable and high real-time features, simplified system design, improved the system's real-time monitoring capabilities and demodulation speed.

Optical fiber sensors (OFS) play an important role in modern intellectualized sensing system. A novel optical fiber sensor based on single mode fiber laser is proposed in this paper. The basic elements of the novel fiber laser sensor (FLS) is based in the fact that the output power of fiber laser is influenced by the loss which caused by the absorption loss of analyte in evanescent field of the fiber. The action of the fiber laser sensor is theoretical investigated using two-level system rate equations. The function which contacted the output power of the fiber laser and the absorption loss of analyte is build upon the complex refraction index of the analyte and the loss of the resonant cavity of the fiber laser though evanescent field. The relative sensitivity of the fiber laser sensor is given finally.

A Fiber Bragg gratings (FBG) Interrogation scheme with scan fiber laser was demonstrated. The ring cavity scan fiber laser was investigated and the scan fiber laser module was made and test, the 200Hz scan frequency, ~0.02nm line width, more than 40nm scan range and more than 1 mW output power were obtained. A 12 channels, 20 FBGs per channel FBG interrogator was made with this laser module and the high speed signal process circuit base on FPGA. The centroid finding method which has advantage on interrogation speed and accurate was taken for finding the peak of the return FBG spectrum. The FBG interrogator was test and less than 3pm standard deviation with 200Hz scan frequency were obtained.

Porous silicon has attracted a great deal of attention and research for biochemical sensing applications. In this study, we report a novel porous silicon based resonant grating filters as an optical sensor platform. A narrow bandwidth in the reflectance spectrum is shown of this porous silicon grating filters and this resonance dip shift obviously after little infiltration. This research also played a potential role for the extensive applications in all-silicon biosensor.

The signal-to-noise ratio (SNR) enhancement using polarization scrambler, narrowband-stop grating and cumulative average processing in Brillouin optical time domain reflectometer (BOTDR) is studied experimentally. Compared to the result without these methods, it is confirmed that these techniques can provide the SNR enhancement in our experiment. This makes it possible to perform a better detection threshold and resolution. The experiment result shows that a temperature resolution of 2°C with a spatial resolution of 3 m is achieved on our BOTDR sensor system.

The detection abilities of PGC scheme dealing with the single frequency signal are investigated, based on which, the frequency domain of the signal is analyzed. Based on the Bessel function theoretic, the mathematical model has been established to analyze the performance of interferometric fiber-optic sensor under the PGC demodulation scheme. The spectrums of interferometer output signals are analyzed when the input signal is single frequency signal and multifrequency signal. Simulation results show that the dynamic domain upper limit of fiber-optic sensor when it operates with the multi-frequency signal must be much smaller than that it operates the single frequency signal.

Using the finite element method to simulate THz photonic crystal fiber(PCF)transmission and sensing characteristics. According to solid TPCF guidance, the refractive index, attenuation and relativity sensitivity were analyzed. And we analyzed firstly the transformation of PCF hole-shape to the influence of sensing on THz wave region. Then we simulate and calculate THz high density polyethylene PCF(HDPE-PCF) some parameters, at last the design considerations were given.

We describe in this paper a near infrared (NIR) Stokes polarimeter. This instrument measures the Stokes parameters of a light beam that exits an optical fiber. The key components of this polarimeter include two photoelastic modulators (PEMs) that operate at different resonant frequencies, a calcite analyzer and a Ge-photodiode detector. The two PEMs in the instrument are oriented at 0° and 45°, respectively, and the analyzer is oriented at 22.5°. The electronic signal from the detector is processed using two different demodulation methods. The normalized Stokes parameters are calculated and displayed on the Poincare sphere. We have shown the high accuracy, sensitivity and stability of this instrument in measuring normalized Stokes parameters.

Structural Health Monitoring (SHM) has assumed a significant role in assessing the structures safety and integrity. SHM can be understood as the integration of sensing intelligence and possibly also actuation devices to allow the structure loading and damaging conditions to be recorded, analyzed, localized and predicted in such a way that non-destructive testing becomes an integral part of the structure. SHM sensing requirements are very well suited for fiber optic sensing technology. So in this paper, after a very brief introduction of the basic SHM concepts, the main fiber optic technologies for this application will be reviewed, several examples and the main current technical challenges will be addressed and, finally, the conclusions summarized.

This paper presents a fast estimation method for feedback level factor C of a self-mixing interferometry (SMI) system. The reconstruction of a displacement waveform using a SMI signal needs to know a C value. However, it is difficult to maintain a constant C value during the reconstruction process. We study the features of the reconstructed displacement waveforms incorporating different pre-set C values and classify waveforms into two types. Bisection method is introduced in our method for fast estimating C value. The effectiveness of our proposed method has been verified by both simulation and experimental data.

A novel long-period fiber grating (LPG) refractive index sensor is presented for the measurements of ambient refractive indices which are higher than that of the fiber cladding. As the measurement parameter, the transmission power of the core mode is interrogated at a single wavelength where the core mode and a leaky mode are phase-matched. Firstly, the couplings of the core mode to leaky modes in the novel structure are analyzed by using complex coupled-mode theory, and then classified into three cases analogous to those in the damped oscillations. The power evolutions of the core mode in the couplings are thus intuitively understood. Based on these, for the first time, we demonstrate, with optimized design parameters the transmission power of the core mode is rather sensitive to the change of a higher ambient refractive index at resonant wavelengths. Then we focus on two optimization objectives. One is to enlarge the operational range while keeping given sensitivity, the other is to enhance the sensitivity within a given operational range. Finally, we demonstrate the operational range of the LPG refractive index sensor can be from 1.46 to 1.7 with a sensitivity of ~10^-4, while for a given operational range from 1.455 to 1.465, the sensitivity can be ~10^-6, if assuming the dynamic range of the power is less than 30dB and the measurement resolution is 0.01dB for both cases.

According to the requirement of single-component toxic gases recognition and trace concentration measurement, a novel gas-sensitive sensor array is developed, which chooses metallic porphyrin as sensitive material. Moreover, the multi-spot sensor array detector is designed based on the absorption spectrum measurement and multi-spot measurement. This paper focuses on the structural design of the system and the establishment of the spectral analysis method. The model of after-spectrophotometric structure is adopted by the detector. The entire hardware platform is implemented based on S3C44B0 & μC/OS-II embedded system. In addition, this paper puts forward a recognition model, that combines Principal Component Analysis (PCA) with BP Artificial Neural Networks (BPANN), and an algorithm for trace concentration measurement, based on visible light absorption spectrum analysis. The experimental results show that the correct rate of prediction for 50 unknown samples is 98%, and the maximum relative measuring error is 3%.

A new type of evanescent field sensors based on a doubly cladding single mode fiber is proposed. The theoretical analysis shows that the measurable refractive index (RI) ranges for the sensors are limited in the single mode in the fiber becoming leaky and the range is less than the RI difference between the core and the cladding of the fibers. Two temperature sensors and a humidity sensor were fabricated. One temperature sensor showed a good linear response in a range of 60°C, the modulation depth of 40 dB, and the insertion loss of -1.4 dB. The humidity sensors fabricated by agarose gel had a measurable moisture range of 16 ~ 100% of RH. Its optical power variation with humidity is 8.5 dB and insertion loss is 3.9 dB. We confirmed that the DC single mode fiber sensors became a new type of intensity sensors characterized in good linear response, low insertion loss, high modulation depth, and low cost in fabrication.

A new demodulation technique based on diffraction grating is proposed for high speed application. Compared with tunable filter method, the diffraction grating method has the advantages of potential high interrogation speed, high energy efficiency, no sweeping movements, which makes it a competitive interrogation method in certain field such as dynamic strain monitoring. The optical layout is crucial to guarantee the required performance of the interrogator. A structure which consists of two diffraction gratings, a fiber collimator, a reflection mirror, and a detector is adopted in the consideration of spectrum resolution, optical aberration, and geometrical size. The initial parameters for the structure are figured out by the optical path calculation involving the coefficient of the employed optical elements. The optimized procedure is following sequentially in order to minimize the aberration and obtain the pre-defined specifications theoretically. As the central wavelength for the interrogator is 1550nm, the InGaAs linear array sensor is introduced as the photoelectrical detector. Experiment of demodulation for FBG sensing system is carried out to verify the feasibility of this technique. The wavelength resolution for the interrogator is 1pm, and the demodulation speed is about 2kHz.

The phase/birefringence sensitivities of the fundamental mode of air-silica microstructure optical fibers to strain and pressure are investigated. Theoretical models are built for both hollow-core photonic bandgap fibers and solid-core highly non-linear photonic crystal fibers to study the effects of axial strain, lateral pressure, and acoustic pressure on the fiber length and the effective refractive indexes of the fundamental mode. Numerical simulation shows that the phase/birefringence sensitivity to pressure of a hollow-core photonic bandgap fiber depends strongly on the thickness of the outer solid-silica layer and the air-filling ratio of the microstructure inner-cladding, and the normalized phase sensitivity to acoustic pressure can be 35 dB higher than that of the conventional single mode fiber. Potential applications of the microstructure optical fibers for high sensitivity hydrophones and novel polarization controllers are discussed.

Two kinds of self-loading Farby-Perot (F-P) fiber sensors were prepared by creating micro-grooves on side-face of single mode fiber-28 (SMF-28) and photonic crystal fiber (PCF) with 157 nm excimer laser. Self-loading F-P interference fringe shifts were measured under different temperature, stress and alcohol solution. Temperature sensing experiments show that the sensitivity of PCF and SMF F-P sensors are 0.0580nm/°C and 0.0535nm/°C when the temperature ranges from 30 °C to100 °C. The interference fringe shifts of PCF and SMF F-P sensors are 1.6 nm and 2.2 nm when they were loaded with 80 μm elongation along fiber axis, which correspond to stress sensitivity of 1.41pm/με and 1.50pm/με respectively. The interference fringe shifts of the SMF F-P sensor and the all-solid PCF sensor are 0.4775nm and 0.3490nm when the quality percentage of alcohol changes from 0 to 99.99%.

The amount of light is an important issue in several scenarios ranging from scenic design, light pollution study, illumination engineering, and agriculture. It is typically determined by using a portable digital light or lux meter. By realizing that the proliferation of cell phones is currently tremendous, this paper proposes for the first time a low-cost cell phone based digital light meter. Our innovative idea comes from the fact that the digital camera built into the cell phone is functioned as a two-dimensional light sensitive device and the captured image can be made diffuse. In this way, the diffused image is correlated to the corresponding light level by the built-in microprocessor of the cell phone and our specific algorithm embedded. Our experiment using a typical cell phone embedded with a digital camera and our JAVA program will be discussed.

The purpose of this work is the development of a high sensitivity and biocompatibility Fiber-Optic hydrophone for invivo ultrasound measurements. The selected sensing element- chitosan diaphragm allows matched-load condition due to its relatively permeable property. Chitosan is a natural polysaccharide which considered as biocompatible and biodegradable material that can be safe in performing the in-vivo measurement. The configuration of the sensor is based on the fiber-optic Fabry-Perot interferometry which offers good spatial resolution in the tens of MHz range [1] and robust response. Significant applications of the proposed sensor are in vivo micro-imaging [2], in-vivo lithotripsy measurement [3] or event the laboratory characterization of medical ultrasound sources. In this paper, the performance of the sensor is characterized by comparison with a PVDF needle hydrophone in term of sensitivity, frequency response and directivity.

Specialty optical fibers have been introduced and developed with unusual guiding structures and novel applications. The one of technical challenges to develop the refractive index guided microstructured specialty fibers is how to realize the low loss link between the traditional fiber and specialty optical fiber. In order to insert the microstructured fiber based devices into the standard single mode fiber system, several linkage approaches have been developed and demonstrated. In this paper, we have summarized the recently research progress related with this issue.

Surface plasmon resonance (SPR) sensors with spectral interrogation provide a high refractive index resolution, a large dynamic range and a fixed optical detection module. In this work, we propose a new spectral detection unit that uses only one spectrometer to measure the SPR spectrum from multiple sensing spots rapidly and serially without any mechanical movement. This spectral detection unit is designed based on a spatial light modulator (SLM) configured as a programmable optical aperture for the spectrometer. To demonstrate this concept, a five-channel SPR sensor was built based on the proposed multichannel detection unit and we evaluated the device performance using a refractive index test. The average device refractive index resolution was 1.4 x 10^-6 refractive index units (RIU).

A signal demodulation scheme based on heterodyne technique is demonstrated, which can help fiber-optic hydrophone system meet the demand of large dynamic range and large scale multiplexing. Optical system based on the heterodyne demodulation is given. Reference signal in the demodulation procedure is obtained from the optical heterodyne output, which is quite different from other reported heterodyne techniques. This method not only simplifies RF electronics, but also eliminates the effects of frequency shift vibration generated by the acoustic-optic modulators. Demodulation algorithm is presented and the maximum signal processing capability is analyze. Experiments are carried out and the results show that a signal with a frequency of 1kHz and amplitude of 40rad could be demodulated without distortion when the heterodyne frequency is 64kHz. The same signal is demodulated using PGC scheme with a modulating frequency equal to the heterodyne frequency, and the result shows distortion. Comparing the two demodulation methods verifies that the system we have designed works well and is more suitable for the detection of large signal. Besides, this architecture of system offering advantage of easy to be time-division multiplexed. Together with wavelength-division multiplexing, it demonstrates the potential for the fiber-optic hydrophone to achieve large-scale arrays with high dynamic range.

We report a low-cost interrogator for fiber-optic interferometric and Bragg grating sensors. The interrogator is based on a compact optical path scanner which is made by splicing a hollow fiber to a single mode fiber and by sealing a segment of air and a segment of thermally expanded liquid inside the hollow fiber. The facets between the fiber-air interface and the air-liquid interface reflect the light from the single mode fiber back, and the optical path difference between the two facets can be controlled by changing the temperature of the liquid. When the compact optical path scanner is place inside a white light interferometer together with a sensing fiber-optic Fabry-Perot interferometer, the optical path difference of the sensing interferometer can be decoded as the optical path difference of the scanner when the interference signal gets maximum. The decoding accuracy of such an interferometer interrogation system was measured to be 14 nm over a range of 40 μm. The compact optical path scanner can also be used to form a wavelength meter, which can be applied to decode the Bragg wavelength of a fiber Bragg grating sensor. A decoding accuracy of 3.5 pm was obtained.

The tropospheric SO₂ in Pearl River delta region was firstly measured by airborne Multi Axis Differential Optical Absorption Spectroscopy in China on 10 December, 2008. The SO₂ slant columns were derived with DOAS method in the wavelength from 310~ 325nm and the vertical columns were retrieved by radiative transfer model SCIATRAN. High values were observed near power plant regions with the vertical column density values higher than 8x10¹⁶molec./cm² in the measurement. Combining with the meteorological data from local station the SO₂ flux from the power plant was calculated, the emission flux of SO₂ was about 2.59x10²⁵molec./s. Over the city of Zhuhai, the observed SO₂ vertical column density was 2.46x10¹⁶molec./cm². This is in good agreement with ground-based MAX-DOAS of 2.62x10¹⁶molec./cm² if the same aerosol parameter settings and a well mixed boundary layer of 1000 m is assumed.

A Fabry-Perot interference enhanced surface plasmon resonance (SPR) sensor was designed and analyzed numerically. In this paper, a micro-fluidic channel with two parallel interfaces formed on the metal film of an angularinterrogated SPR sensor was employed. The shift of the narrow reflection dips as a function of the refractive index change of the fluid (angular sensitivity Sθ ) was very high. Meanwhile, the angular dip width δθ_FWHM was very narrow (<0.01°) and can be adjusted by changing the thickness of the resonant cavity. The corresponding intrinsic sensitivity IS = S_θ/δθ_FWHM higher than 10⁵ RIU^-1 around the resonant angle can be achieved.

After several decades, the development and application of absorptive fiber semiconductor temperature sensor have been slowed down for the difficulty to satisfy the critical requirement of the special wavelength and broadband lightsource. On the other hand, temperature-dependent refractive index, i.e., thermal-optic effect of the semiconductor materials has not gained much attention beyond the semiconductor processing industry. With a much larger temperature-dependent refractive index than the common optical materials, such as glass and quartz, many semiconductor are also popular coating materials on fiber. Taking advantage of the interaction of large temperature-dependent refractive index and temperature-dependant absorption coefficient of semiconductor, we manage to build a very small, sensitive, simple and low cost fiber temperature probe operating at communication wavelength. We develop a sensor model for an optical fiber-germanium (Ge) film type temperature sensor based on the modified optical film theory, which involves temperature-dependent absorption below infrared transparent window of Ge as second major cause for reflectivity change beside thermal optical effect. Investigation of the feasibility and sensitivity of the fiber-film probe has been carried out theoretically and experimentally within the temperature regime of -20-120°C, which is the most used temperature range for industry monitoring. A sensitivity of reflectivity change about 0.001/°C has been demonstrated by the experimental results of the novel designed sensor. Further discussion on the potential of sensitivity and further application are presented.

A new-conceptual fiber-optic gyroscope is introduced. The gyroscope employs the two newly-emerged novel technologies: the optical frequency-modulated continuous-wave (FMCW) interference, and the differential fiber-optic gyroscope, and therefore, it can overcome the problems in the traditional fiber-optic gyroscopes, such as temperature drift and poor long-term stability. The FMCW interference, which was originally investigated in radar technology, has been successfully used to construct various fiber-optic interferometers and sensors. The advantages of this technology include accurate calibration of the phase, simple count of fringes, and easy signal processing. The interest in the application of the FMCW technique to rotation sensing has been growing for a long period. The problem in the FMCW fiber-optic gyroscope is that the gyroscope must be an unbalanced, and the initial optical path difference in the gyroscope will cause an unexpected non-reciprocal phase drift if the environmental conditions are unstable. This paper reports a differential FMCW fiber-optic gyroscope. The advantages of this fiber-optic gyroscope include: (1) Due to the nature of the differential interferometer structure, the unexpected non-reciprocal phase drift is automatically removed, and the calibration fact of the gyroscope is automatically doubled. (2) Benefited from the FMCW technology, this gyroscope has no zero-sensitivity point problem, and it has a higher resolution and a larger dynamic range.

Gas analysis based on tunable diode laser absorption spectroscopy (TDLAS) provides features of high sensitivity, fast response and high selectivity. When target gas concentration is below a few parts-per-million spectrometers become more and more sensitive towards noise, interference, drift effects and background changes associated with low level signals. It is purpose of this paper to address some of the problems which are encountered at this low signal levels and to describe a signal processing strategy for gas monitoring with wavelet transform. Different parameters of wavelet by taking gas detection of H₂S as an illustration are studied and an improved wavelet-based signal enhancement process is proposed based on the feature of TDLAS second-harmonic signal. The algorithm uses bior3.9 wavelet basic function and multi-resolution decomposition. The results show a plausible improvement in performance of TDLAS system and enhancement of detection limit from 10ppm to hundreds of ppb level under various noise conditions.

Based on the increased interest for optical fibres development for the use in smart structures and sensors, this study has aimed to investigate the chemical reliability of standard commercial epoxy-acrylate polymer coated fibres subjected to aggressive chemical reagents in gaseous and liquid phase, such as acetylene, ammoniac, dimethyl sulfoxide. Multimode optical fibre was exposed to gaseous reagents for different durations after prior vide exposure. Tensile testing results were treated using Weibull statistics. A comparison of mean failure strength of as-aged fibres to the water influence for similar exposure duration has revealed the highest sensitivity to dimethyl sulfoxide reagent.

Increased demands on air quality have created incentives for new methods to monitor gas pollution. In this paper we will present an online gas analyzer for industrial flue pollution monitoring based on tunable diode laser absorption spectroscopy (TDLAS) technology. Signal measurements with a sensitive device inevitably suffer from the predictable or unpredictable sources such as intensity fluctuations and the laser output wavelength dithers. In order to eliminate or at least reduce the measurement uncertainty and gain high reliability, a close-circle digital-control module with functions of digital signal generator, digital lock-in-amplifier (D-LIA), data acquisition and data processing has been developed to substitute the previous independent signal generator board, analog lock-in-amplifier and data acquisition card in our TDLAS system. With the help of the digital-control module and the advanced digital signal processing techniques the performance of the TDLAS system has demonstrated great improvement in long term field tests.

An image spectrometer of a spatial remote sensing satellite requires shortwave band ranging from 2.1μm to 3μm which is one of the most important bands in remote sensing. We designed an infrared sub-system of the image spectrometer using a homemade 640x1 InGaAs shortwave infrared sensor working on FPA system which requires high uniformity and low level of dark current. The working temperature should be -15±0.2 Degree Celsius. This paper compares three different kinds of methods to control temperature of the sensor. First design uses a temperature control chip Max1978 from Maxim Company. Second design uses ADN8830 from ANALOG Company. Third design is based on FPGA device APA300. Experiment shows that MAX1978 has driving mosfet inside its chip which makes the stability is not appropriate for this homemade shortwave sensor. While the ADN8830 the supply power is limited to 5V, which also limits the driving power of the chip, experiments show that ADN8830 works very well when the voltage is below 5V, but the result is not acceptable when sensor demand more driving current. The FPGA design covers all the disadvantages above, but it introduced a new problem, the electrical circuit takes much more board resources than MAX1978 and ADN8830.

The dispersion properties of LPCF were fully analyzed by using the beam propagation method (BPM). It is shown that the zero dispersion wavelengh (ZDW) of LPCF can be altered to the designed value in a certain range without the modification of the geometric structure. This property is useful for sensing and nonlinear optics applications.

At present, laser optical pumping magnetometer of sensitivity is continuous improved and can measure the range from Earth magnetic field to the bio-magnetic field. In the bio-magnetic field, magnetocardiography (MCG) is paid also more and more attention. In this paper, we will discuss cesium optically pumped magnetometer theoretical analysis, system design, the magnetic field gradient measuring principle. On this basis, we build optically pumped magnetometer in a gradient structure for the cardiac magnetic measurements and filter through the wavelet transform. Based on optical pumping magnetometer measuring MCG will be applied in life science, clinical medicine and other fields.

In this paper, the chromatic confocal technique application in position measurement is studyed theoretically and experimentally. Firstly, a set of refractive lenses are designed and a position measurement device is established for this purpose. Then, calibration of wavelength-depth relationship has been performed. The calibration results accords with the theoretical design results well. Third, influence of the detector pinhole size on axial resolution of the measurement system is analyzed. It is clear from numerical simulation that the full width of half maximum (FWHM) of spectral distribution on the detector will increase with enlargement of pinhole size, which makes axial resolution decrease. The experiment results also disclose identical tendency. It can be concluded that the position measurement system can realize rapid position measurement with higher precision.

In this paper, we report a new facile method for the synthesis of water-soluble PbS quantum dots (QDs), using dihydrolipoic acid (DHLA) as a stabilizer. The prepared QDs were characterized by optical techniques and high-resolution transmission electron microscopy (TEM). Next, these water-soluble luminescent PbS QDs were further used to detect copper (II). The obtained experimental results show that the fluorescence of the PbS QDs could be markedly quenched by Cu(II) whereas approximate concentrations of other physiologically relevant cations, such as Zn(II), Ca(II), Mg(II), Mn(II), Na(I) and K(I) etc., almost did not interfere with the fluorescence quenching progress of copper ions. Based on this, a simple and rapid method for Cu(II) determination was developed. Under optimal conditions, the response was linearly proportional to the copper(II) concentration in the range of 1 to 11.5x10^-8 mol•L^-1, with a correlation coefficient of 0.995. Hence, aqueous DHLA-stabilized PbS QDs may be a promising fluorescent probe in sensing copper(II) selectively.

The enhancement of evanescent waves in multilayer planar waveguides with a uniaxially anisotropic metamaterials layer is investigated. Without loss of generality, we assume that the anisotropic metamaterials have an arbitrary angle between the optical axis and the interface, and then we derive the characteristic equations and the analytical expression of energy flux of this waveguides. It is found that the enhancement factor increases rapidly at first with increasing of the thickness of the metamaterials in the case when the optical axis is parallel to or normal to the interface, namely the angle is equal to 0 or π/2. The enhancement factor eventually reaches its maximum when complete surface polaritons are established at the boundary between the metamaterials and the cladding [D.-K. Qing, G. Chen, Appl. Phy. Lett. 84(5), 669-671 (2004).]. Numerical results confirm our theoretical analysis.

In this paper, a high birefringence loop mirror sensing head was introduced, and its temperature, strain sensing properties with panda-type HBFLM were analyzed and researched in experiment. Experimental results showed that both the temperature and strain sensors have high sensitivity, linearity. Its temperature sensitivity reached 1.41 nm/°C, with the sensitivity linearity was up to 0.99968; Its strain sensitivity was 0.02362 nm /με, when the linearity between strain and wavelength shifts was above 0.99912. This panda HBFLM temperature sensor can be widely used in some industries requiring high sensitivity, miniaturization of structure, and stability, such as high voltage cables, oil temperature measurement, and large monitoring structure fields such as detecting important buildings, bridges, dams.

An image spectrometer of a spatial remote sensing satellite requires shortwave band range from 2.1μm to 3μm which is one of the most important bands in remote sensing. We designed an infrared sub-system of the image spectrometer using a homemade 640x1 InGaAs shortwave infrared sensor working on FPA system which requires high uniformity and low level of dark current. The working temperature should be -15±0.2 Degree Celsius. This paper studies the model of noise for focal plane array (FPA) system, investigated the relationship with temperature and dark current noise, and adopts Incremental PID algorithm to generate PWM wave in order to control the temperature of the sensor. There are four modules compose of the FPGA module design. All of the modules are coded by VHDL and implemented in FPGA device APA300. Experiment shows the intelligent temperature control system succeeds in controlling the temperature of the sensor.

We investigate an ultra-weak feedback effect of DBR fiber lasers based on the steady-state rate equations. The ultra-weak-feedback effects of DBR fiber lasers are introduced by the fiber Rayleigh scattering and the scattering of the fiber splicing point. The output powers of the DBR fiber lasers are modulated when their feedbacks are modulated. A simple vibration sensing scheme based on this effect is proposed and demonstrated. The optimized design of the sensing scheme is discussed at last.

We study a novel multi-parameter sensing device based on writing Bragg grating in the multimode fiber of single-multi-single mode fiber structure. The theoretical analysis of the novel device is given based on a compound coupled mode theory. The simulation results of strain and temperature sensing simultaneous are demonstrated, and the elementary results of the refractive index sensing with temperature-compensation are also given.

We have studied the properties of defect modes in one-dimensional ternary photonic crystal with one defect layer using transfer matrix method(TMM). we first compared the transmission spectra of one dimensional ternary photonic crystal with that of one dimensional binary photonic crystal, and found more bandgaps in the ternary structures. Then we are interested in the defect mode properties of the ternary structures, especially the optical sensing abilities. In the special bandgap owned only by the ternary photonic crystals, the defect modes are found to be very sensitive for sensing very small refractive index changes or very small thickness modulations of the defect layer medium. The defect mode wavelength could shift by 3nm for each refractive index change of 0.006, and the defect mode wavelength could shift by 13nm for each thickness change of 10nm. Finally we introduced a negative-refractive-index defect layer into the ternary structure and found that the defect mode wavelength could shift even by 27nm (two times of 13nm) for each thickness change of 10nm.

This paper presents comprehensive research on fused-tapered Bragg reflection integrative FGC where high-quality and easy-fabricating are two main considerations. The technical procedure of FGC fabrication is fixed after a series of experiments. The possible factors that may determine the device performance were carefully analyzed. The fused-tapered FGC was successfully fabricated and a novel testing system was established. The adding and dropping functions of FGC were investigated experimentally.

A C₂H₅OH gas sensor based on a LPFG coated with the T_iO₂ nano-film is presented.Based on LPmodes,the four-layer model is studied the change of the effective refractive indics and the resonance wavelength of cladding modes as the thickness of overlay increased.The elementary experimental results show that the wavelength of the LPFG loss peak is shifted by ~1.7nm for the case of the T_iO₂ nano-film of ~80nm in thickness when the concentration of surrounding C₂H₅OH gas is 1000ppm. And the sensitivity is 1.7 10^-3 nm/ppm. The results indicate that the LPFG sensor is highly sensitive to C₂H₅OH gas and the sensing scheme is feasible.

With the development of the society and economy and the improvement of living standards, people need more and more pressing security. Perimeter security alarm system is widely regarded as the first line of defense. A highly sensitive Fiber Bragg grating (FBG) vibration sensor based on the theory of the string vibration, combined with neural network adaptive dynamic programming algorithm for the perimeter security alarm system make the detection intelligently. Intelligent information processing unit identify the true cause of the vibration of the invasion or the natural environment by analyzing the frequency of vibration signals, energy, amplitude and duration. Compared with traditional perimeter security alarm systems, such as infrared perimeter security system and electric fence system, FBG perimeter security alarm system takes outdoor passive structures, free of electromagnetic interference, transmission distance through optical fiber can be as long as 20 km It is able to detect the location of event within short period of time (high-speed response, less than 3 second).This system can locate the fiber cable's breaking sites and alarm automatically if the cable were be cut. And the system can prevent effectively the false alarm from small animals, birds, strong wind, scattering things, snowfalls and vibration of sensor line itself. It can also be integrated into other security systems. This system can be widely used in variety fields such as military bases, nuclear sites, airports, warehouses, prisons, residence community etc. It will be a new force of perimeter security technology.

VNIR multi-spectral image sensor has wide applications in remote sensing and imaging spectroscopy. An image spectrometer of a spatial remote programmable push-broom sensing satellite requires visible near infrared band ranges from 0.4μm to 1.04μm which is one of the most important bands in remote sensing. This paper introduces a method of design the driving system for 1024x1024 VNIR CCD sensor for programmable push-broom remote sensing. The digital driving signal is generated by the FPGA device. There are seven modules in the FPGA program and all the modules are coded by VHDL. The driving system have five mainly functions: drive the sensor as the demand of timing schedule, control the AD convert device to work, get the parameter via RS232 from control platform, process the data input from the AD device, output the processed data to PCI sample card to display in computer end. All the modules above succeed working on FPGA device APA600. This paper also introduced several important keys when designing the driving system including module synchronization, critical path optimization.

Thermal properties and spectroscopic properties of the glass micro-sphere were presented in this paper. The Er³⁺ emission spectra of a kind of Erbium-doped glass microsphere were measured and discussed under 532nm excitation in a series of temperatures. The change in the temperature of the microsphere leads to a change in both the size and the index of refraction of the sphere, which results in the resonance shift of the peaks of whispering gallery modes in emission spectra. The temperature of the environment surrounding the sphere can be determined by monitoring the shift, which allows us to calibrate the sensing function of the shift proportional to temperature. Based on the thermal effects, we propose a novel optical temperature sensor using micrometer-sized sphere.

Heart sound includes a lot of physiological and pathological information of heart and blood vessel. Heart sound detecting is an important method to gain the heart status, and has important significance to early diagnoses of cardiopathy. In order to improve sensitivity and reduce noise, a heart sound measurement method based on fiber Bragg grating was researched. By the vibration principle of plane round diaphragm, a heart sound sensor structure of fiber Bragg grating was designed and a heart sound sensing mathematical model was established. A formula of heart sound sensitivity was deduced and the theoretical sensitivity of the designed sensor is 957.11pm/KPa. Based on matched grating method, the experiment system was built, by which the excursion of reflected wavelength of the sensing grating was detected and the information of heart sound was obtained. Experiments show that the designed sensor can detect the heart sound and the reflected wavelength variety range is about 70pm. When the sampling frequency is 1 KHz, the extracted heart sound waveform by using the db4 wavelet has the same characteristics with a standard heart sound sensor.

The demodulations of the Bragg wavelength shifts are significant and gaining more and more interesting. Detecting the wavelength shifts based on the interferometry has a very high sensitivity. The unbalanced Mach-Zehnder interferometer system can translate the Bragg wavelength of FBGs caused by the strain into the phase information. The tested strain can be obtained through the phase variation by the three-step phase-shifting method. A finite element model is built up and theoretical analysis has been done. Series experiments measuring the strain properties of the cantilever are carried on. The results show that the tested strain and the changed phase have a linear relationship. The unbalanced Mach-Zehnder interferometer system owns a high-sensitivity and accuracy.

In the field of micro laser welding, besides the special requirement in the parameter of lasers, the locating in welding points accurately is very important. The article adopt position sensitive detector (PSD) as hard core, combine optic system, electric circuits and PC and software processing, confirm the location of welding points. The signal detection circuits adopt the special integrate circuit H-2476 to process weak signal. It is an integrated circuit for high-speed, high-sensitivity optical range finding, which has stronger noiseproof feature, combine digital filter arithmetic, carry out repair the any non-ideal factors, increasing the measure precision. The amplifier adopt programmable amplifier LTC6915. The system adapt two dimension stepping motor drive the workbench, computer and corresponding software processing, make sure the location of spot weld. According to different workpieces to design the clamps. The system on-line detect PSD 's output signal in the moving processing. At the workbench moves in the X direction, the filaments offset is detected dynamic. Analyze the X axes moving sampling signal direction could be estimate the Y axes moving direction, and regulate the Y axes moving values. The workbench driver adopt A3979, it is a stepping motor driver with insert transducer and operate easily. It adapts the requirement of location in micro laser welding fields, real-time control to adjust by computer. It can be content up 20 μm's laser micro welding requirement on the whole. Using laser powder cladding technology achieve inter-penetration welding of high quality and reliability.

The simulation based on the finite-element (FE) method plays an important role in the investigation of the intra-body communication (IBC). In this paper, the method for modeling the whole human body based on the finite-element method is proposed, while a finite-element model of the whole human body used for the simulations of the waveguide intra-body communication has been developed. Finally, the simulations of the waveguide IBC with different signal transmission paths have been achieved by using the developed finite-element model. Moreover, both the potential distributions and the signal attenuations of the simulation results are discussed in detail, which indicate that the proposed method and model offer the significant advantages in the theoretical analysis and the system design of the waveguide intra-body communication.

Heavy metal pollution emerges as the industry develops, which threads human health severely. Cd is a kind of supervirulent heavy metal which needs inspection for food safety. This thesis studies on the immunosensor technology based on surface plasmon resonance (SPR), successfully detects Cd and introduces the principle of SPR immunosensor detection system. Cd-iEDTA-BSA (complete antigen of Cd) immunosensor has been made by the methods of hybridization product and Cd-iEDTA-BSA antibody. There are clear 3*3 arrays on the sensor chip. Two SPR detection methods of imaging and scanning have been applied to detect the immunoreaction. The picture captured by SPR imaging system can directly observe the phenomena of the surface plasmon resonance on the sample arrays and the immunoreaction from the view of the resonance angle. Besides, the excess content of Cd can be found out by finding in the sample the matched material on the probe of sensor chip. After the immunoreaction the molecular weight of antigen-antibody compound which forms on the surface of the chip increases, so does the refractive index as well as the resonance angle. The resonance system can detect the resonance angle and the refractive index of each position on the sensor chip precisely, and draws the resonance curves. The arrays' resonance curves reflecting the immunocreation have a clear displacement which indicates the increase of the resonance angle as well as the refractive index. The sensitivity of the scanning surface plasmon resonance detection system is higher than the imaging one, which is more convenient and consumes shorter time.

The axial strain of bending four-core fiber Bragg gratings (4CF-FBG), bending side-polished FBG (D-FBG) and D-4CF-FBG is analyzed with mechanics of materials. Bending sensitivity characteristic of Bragg wavelength's shift is obtained. D-4CF-FBG's bending sensitivity is higher than that of 4CF-FBG and D-FBG, and D-4CF-FBG's bending sensitivity with respect to the different thickness of side-polished is several times to several decuple higher than D-FBG. The result was helpful for the design of high sensitivity fiber Bragg grating bending device or sensor system.

In this paper, a MOEMS accelerometer with integrated-grating-based optical interference detection is presented. The acceleration sensor consists of an integrated grating on a transparent substrate and a mechanical part of a bulk silicon proof mass suspended by cantilevers attached to the silicon support substrate. The proof mass and cantilevers were fabricated with a two-mask process on one silicon-on-insulator (SOI) wafer. A phase sensitive diffractive grating was formed with the grating and the upper surface of the proof mass, which acts as a reflective mirror. Illuminating the grating with coherent light generates a series of diffracted optical beams, whose angles remain fixed, but whose intensities are modulated by the relative distance between the grating and the proof mass. Distance alteration caused by vibratory accelerations, changed the intensities of the diffracted beams, which could be detected by a differential circuit to get the variety of acceleration. Experimental results demonstrated that this MOEMS accelerometer has good performance with sensitivity of 3.63x10⁴V/g and a dynamic range of ±5g.

A novel signals' receiving and data processing approach is proposed for optical scattering signal transmitting. This proposed approach consist of three steps: firstly, the signals are received by two detectors in terms of spacial diversity synchronously, and then collected by high speed data collection card afterwards; Secondly, the 1.5 dimension spectrums of the collected signals in step 1 are calculated; Finally, the cross-correlation of the 1.5 dimension spectrums is used to decrease the non-gauss noise. In order to validate the proposed approach, an optical scattering signal receiving system has been designed based on two detectors and other ordinary instruments. The experimental results indicate that the designed system can demodulate the optical scattering signals accurately even if the noise-signal ratio (SNR) is as low as -25dB. It proves to be effective and adequate in the secure optical scattering communication.

As temperature detection is widely required in industrial production and the optical fiber sensor has such characters as simple structure, small size, all-fiber-based, remote measurement and easy to use, we propose a method for the temperature measurement based on the semiconductor temperature-absorption principle. An optical spectro-grating is used to analyze the sensor signals, and a position-sensitive-device is used to record the measurement results. The measurement principle of the sensor system can be described as follows. When a broad-band light source is input, the absorption edge of the semiconductor material will shift with the varied temperature, resulting in the loss of some light with certain light wavelengths if the broad-band light passes through the semiconductor material. An optical spectro-grating is used to split the remained light into different blazed angles due to the wavelengths. A position-sensitive-device is used to record the edge of the light spot, which is varied versus the measured temperature. Sensor structure and measurement principle are introduced. The feasibility is explained theoretically and results shows that temperature measurement resolution of 0.05°C can be obtained.

Recent years, the technology of slow light generations and applications are becoming hot topics, including data buffering in optical communications and optical signal delay. In this paper, we propose the application of slow light in the field of optical sensor and illustrate several principles and structures to enhance the sensitivity of interferometers based on slow light. According to the experiment results, the sensitivity of the interferometers enhance 600 times at most; however, the sensitivity can enhance 10⁷ times in theory; moreover, the volume of the interferometer can be reduced. The miniaturization and precision devices must be applied and researched deeply in the field of sensor and measurement technology.

We evaluate the measurement errors induced by various deleterious effects in an optical passive ring-resonator gyro (OPRG) with a hollow-core photonic bandgap fiber (HC-PBF) sensing coil. The uncertainties in measuring rotation rate due to Kerr, Shupe, and Faraday effects are found to be reduced respectively by 2~3, 1, and 1~2 orders of magnitude as compared with an OPRG with a conventional single mode fiber (SMF) sensing coil of similar parameters. The errors due to shot and coherent backscatter noises are larger for the OPRG made of the current state-of-the-art HC-PBF than for the OPRG with a conventional SMF coil, but are expected to reduce in future with improved fiber manufacture technologies.

Moiré fringe is a traditional subdivision technique in precision displacement measurement. In general, use photodiode as a four-segment sensor. In this paper, we'll introduce a new system for grating subdivision of moiré fringe. The system consists of light source, condenser lens, grating, microscope tube, and CMOS image sensors. Different ways with the traditional image acquisition, there is an angle θ between grating stripe and the optical axis of the microscope system. Therefore, the stripe image which output by the CMOS image sensor becomes oblique. With different method of our previous study, a virtual moiré will form by the oblique stripes superimposed with the CMOS image array, which using digital image processing. The same as traditional method, the movement direction of the virtual moiré fringe is vertical with the direction movement of grating in this system. The virtual moiré fringe will move a space with grating period, the magnification has a relationship with the angle θ. Compare with early study, the largest increase for this system is the average effect of grating measurement system will be fully utilized by virtual moiré formed by CMOS image array. For the subdivision technique use the CMOS image array, system resolution will be large increased too. In this paper, the details of system components will be introduced, the magnification relationship of grating period and tilt angle will be discussed. It can be concluded that virtual moiré subdivision system performs better resolution and precision from experiment results.

A signal demodulation scheme for micro quartz tuning fork gyroscope based on digital correlation demodulation technology is proposed. In the operation of quartz gyroscope the reference signal should be in the resonance state with steady amplitude and the reference signal should be in-phase and has the same frequency with the driving signal. The quartz gyroscope signal processing platform is designed on the foundation of DEC6713 DSP development board successfully. The adaptive algorithm including the reference signal frequency tacking, the amplitude automatic gain controlling, the reference signal phase locking, and complex correlation demodulation are devised, and the algorithm is programmed. It is proved that the digital signal process scheme is feasible by means of experimentation.

Most of the traditional distance measurement using electromagnetic waves or electromagnetic pulse time of flight to obtain distance information. It has been widely used in various fields ranging. Accuracy and high resolution can get by the method. Ranging in many occasions does not need high accuracy and resolution. For example, it can reverse radar, blind obstacle avoidance, etc. This paper presents a new distance measuring device that based on infrared light intensity modulation. Moreover the device combine with the fuzzy control theory, so called fuzzy location device based on infrared light intensity modulation. The device includes the infrared modulation transmission unit, collimating unit, infrared receiver unit, background light sensor unit and data processing unit. If alarm distance is n m, data processing unit set infrared light intensity of infrared modulation transmission unit and the light intensity threshold of infrared receiver unit by look-up table with fuzzy control theory. It is according to the current background light intensity. Once the receiving light intensity exceeds the threshold, the system alerts. The paper expounds the working principle, fuzzy control theory on the domain and fuzzy rules domain, the experimental results of the device and analysis in detail. It shows that the device is small, low cost and suitable for a large number of used when it dose not need high accuracy and resolution measurement

We design a new system for simultaneous distributed measurement of temperature and strain based on both spontaneous Raman and Brillouin backscattered signals. The Raman signal can determine the temperature. Although the Brillouin frequency shift is dependent on both temperature and strain of fiber, once the temperature is determined from the Raman signal, the strain can then be computed from the frequency measurement of the Brillouin signal.

A fiber optic temperature sensor realized by low-birefringence photonic crystal fiber (PCF) based Sagnac loop is demonstrated. Due to the low birefringence of this PCF, only one dip appears in the spectrum when an amplified spontaneous emission (ASE) light source is used. The sensitivity of the temperature measurement of -0.123nm/°C is achieved in the range of 25°C-85°C, and the temperature resolution limited by the 20pm wavelength resolution of the OSA is about 0.16°C.

Laser Doppler vibration measuring system has been widely used in many fields, in order to eliminate the phase fading, phase generated carrier (PGC) homodyne demodulation technology has been applied usually, and dual-optical-channel balanced detection technology has been used to suppress the intensity noise of the light source. However, theoretical analysis reveals that the intensity noise of the light source cannot be eliminate totally due to the modulation, which is still the main noise in the system. In this paper, we consider the influence of the intensity noise of the light source and the shot noise of the detectors. By numerical simulating, we analyze the origin of the noise, especially the influence of remnant intensity noise to signal-to-noise ratio of the system, and find the optimal parameters of the system.

Phase diversity wavefront sensing is a methodology for estimating wavefront aberrations by solving an unconstrained optimization problem from multiple images whose pupil phases differ from one another with a known amount. Due to the large number of unknowns, an efficient numerical technique is required. In this paper, a cost function with appropriate stabilization is given by using least square estimate. Various optimization methods for minimizing the cost function are compared in numerical simulations when the wavefront is described by Zernike polynomials (modal method) and a set of individual pixel values (zonal method). The results show that, because of the less unknown parameters, modal method can achieve higher accuracy than zonal method by using the steepest descent method and the conjugate gradient method. In the solving process, the zonal method has a large number of unknown parameters, thereby it has a lower stability and it is easy to fall into a local extremum. Fortunately, the L-BFGS method can improve this problem efficiently. For its good performance in solving large scale optimization problems, the L-BFGS method is very suited to PD wavefront estimate.

In this paper, an optical Long-period fiber grating (LPG) fabricated by CO₂ laser in side-hole single-mode fiber (SHLPG) for cantilever deflection measurement was demonstrated according with LPG flexural character. resonance wavelength of SHLPG (1547.3nm) has a total blue shift of approximately -0.83nm for deflection ranging from 0 to 40mm, and a red shift of 0.74nm with deflection ranging from 0 to -40mm. The results indicated that the SHLPG owns higher deflection sensitivity than that of normal LPG and fiber Bragg grating. The deflection sensitivity coefficient of SHLPG is -0.202nm/mm. The resonance wavelength shift has a good linear with the deflection increasing. The correlative coefficient is 0.9966. Factual deflection measuring can be got with high sensitivity through SHLPG easily.

This paper introduces the principle of fiber Bragg grating (FBG) sensor, designs and realizes a compact wavelength demodulation system for FBG sensing using a Fabry-Perot (F-P) filter. FPGA is adopted as a main controller to control a D/A converter to produce a sawtooth wave for driving the F-P filter, and to design the data acquisition circuit for collecting the output signals of photoelectric detector. The collected data is processed after transmitting to PC through the data transmission circuit, and then the demodulation of FBG wavelength is completed finally. This compact FBG wavelength demodulation system is expected to have wide applications in on-line monitoring of electric power equipment and large structures.

We have designed and characterized a novel fractal Cantor multilayer porous silicon photonic crystal with a defect embedded in its middle as an optical sensor for sensing of various chemical and biological species. Compared with the common periodic structure one (such as Bragg) and some aperiodic structure (such as Thue-morse), it is more sensitive because of the lower number of interfaces. This research lays the foundation for design all-silicon sensor for biochemical sensing and can also be good applied in excellent filter.

Fiber Bragg Grating sensor is a kind of widely used new sensors. This paper presents a level based on fiber Bragg grating tilt sensor, with the variation of the tilt angle is converted to optical conversion of the change in deformation mechanism to achieve the measured level of relative horizontal angle measurement, sensor-related design theory is given, and to design sensor sensing structure. The sensor adopts fiber grating method to eliminate reference to temperature and metal bellows packaging method to improve the sensitive strain, and through experiments proved the feasibility of this design.

Distributed optical fiber temperature sensor (DTS) system is widely used in temperature measuring projects. In this paper, applications of DTS system in temperature measuring and leakage detecting of dam are studied. Problems and solutions of using DTS system in dam are researched. Two typical engineering applications in the Three Gorges dam and Xin'anjiang hydropower station are studied. Test results are listed in the end.

In order to protect optical system from being discovered by the active laser reconnaissance, the unsymmetrical covering method is proposed to realize the optical system's laser stealth. The theoretical model of the method was established. The laser stealth effect was analyzed and the results indicate that covering a part of optical system's aperture could obscure the echo in both the covered area and its centrosymmetric area. Therefore, the absolute laser stealth could be achieved by covering half of the optical system's aperture, while the optical system still has good performance. An experiment was designed to validate the theoretical analysis results. The experimental results are shown to be in good agreement with the theoretical results. The unsymmetrical covering method is effective to the laser stealth of optical system.

A number of applications of fiber optic sensor for bioluminescence have been widely reported. The key component in fiber optic fluorescent sensing system is sensor probe, whose efficiency will determine the overall sensor performance, and haven't been thoroughly understood in previous studies. Questions about how the probe structural parameters such as length, diameters and N.A. of its fiber components affect the collecting efficiency of the fluorescence signals. In this paper, we present a pinpoint fiber-glass probe aiming at efficient fluorescence collection. According to the geometric optics approach, we model a sensor probe based on the same principle of coupling ratio analysis between a light source and a fiber, and demonstrate the quantitative relations of the fluorescent collecting efficiency and the structural parameters of the probe by simulation and experiment. Our theoretical analysis comes up with a optimal probe geometry which has the highest fluorescent efficiency of the designed fiber optic sensor probe, and reveal detailed relations that the efficiency is direct proportion to the core diameter, NA of receiving fiber, the length and the section radius of the sensing probe, where the ratio of the core diameter to sectional area of the probe is the key factors for the fluorescent efficiency for certain detection accuracy.

The interferometric vibration sensor with quadrature detection can generate orthogonal signals by optical configuration. The influence of the DC component existing in the interferometric orthogonal signals is discussed in this paper. The signals were processed by time derivation and arctangent algorithm to demodulated the analog signals. Theoretical analysis and experimental results prove that this method can be used to eliminate the DC component in the signal, meanwhile, the micro-vibration signals can be measured accurately.

In the present paper, a novel ultrahigh birefringent index-guided triangular-arrayed photonic crystal fiber with two small elliptical air holes in the core is proposed, which guides light by total internal reflection (TIR). The birefringence of PCFs is investigated using full-vector finite-element method. The impacts of the geometrical parameters and position of the elliptical air holes on the properties of birefringence are discussed. Our suggested structures show that the birefringence can be as high as 1.5x10^-2 at 1.55μm wavelength.

Because of a series of advantages such as high sensitivity, non-contact measurement, interferometric vibration sensors have attracted interest from a lot of researchers in vibration sensing field. In this paper, a novel Mach-Zehnder interferomtric vibration sensor which utilizes quadrature detection technology is proposed. In our system, non-polarized light source and 1/4 wave plate is used to obtain two in-phase and quadrature-phase (I/Q) signals. Compared with previous methods, this sensor system has a simple optical configuration and more reliable stability. Theoretical analysis indicates that this sensor can measure the vibration displacement accurately.

We present a perfomance study of stimulated brillouin scattering (SBS) distributed fiber-optic sensing with modified steady-state model. Modified model which introduces a new noise factor B can be utilized to describe SBS process more precise. Harmonic reconstruction algorithm has been conducted based on the modified steady-state model. Comparative results analysis between original steady-state model and modified model will also be given in this thesis.

Two kinds of optical fiber sensors that are fabricated with fiber side polishing technique are proposed and demonstrated experimentally to measure the concentration of acetic acid solution. One kind is side polished fiber Bragg grating (SPFBG) sensor, which is fabricated by side polishing the cladding over the grating region of fiber Bragg grating. The reflective Bragg wavelength of SPFBG sensor shifts when its polished region is overlaid with different concentration of acetic acid solution, so the concentration of acetic acid solution could be measured. Its resolution is 6.67%. The other kind is side polished fiber (SPF) sensor fabricated by single mode fiber whose part of cladding is side polished. The concentration of acetic acid could be measured by the transmitted optical power when polished region is overlaid with acetic acid solution. Its resolution of sensor is 0.55%.

A relative humidity (RH) sensor based on a hybrid fiber grating coated with a moisture sensitive polymer is proposed in this paper. The hybrid fiber grating includes a normal fiber Bragg grating (FBG) and a tilted FBG (TFBG), which are superimposed around the same position of the fiber. The FBG reflects a part of the cladding modes of the TFBG and its intensity changes with the refractive index of the moisture sensitive polymer, which varies when absorbing and desorbing moisture. The optical power interrogation method is simper and more cost-efficient than normal FBG-based relative humidity sensors using wavelength detection method.

A simple novel load sensor has been demonstrated by embedding a uniform fiber Bragg grating (FBG) along the axis of a tapered cylindrical polymer rod. Due to the load-induced nonuniform strain field applied along the length of the FBG, the bandwidth of its reflection spectrum varies linearly with the applied load. By measuring the reflected optical power of the chirped FBG illuminated by a flattened broadband light source, temperature-insensitive measurement of load is realized. It is intensity-modulated so that complex wavelength interrogation system is avoided in the sensor system. In the experiment, the achieved sensitivity is 0.99 nW/N over a range from 0 to 43.12 N. Since the FBG is well protected by embedding in the tapered elastic polymer rod, excellent reliability is expected.

Low-frequency wavelength modulation is introduced to increase sensitivity of intra-cavity absorption gas sensor (ICAGS) system. ICAGS system including erbium-doped fiber amplifier (EDFA), pump laser, tunable fiber Fabry-Perot (F-P) optical filter and gas cell is set up. Using virtual instrument technique, modulation function is generated by LabVIEW software and outputted through the AO ports of data acquisition card to tune the driving voltage of optical filter. The AI ports collect the laser power signals in a synchronous mode. Harmonic spectra can be computed by adopting the method of the Discrete Fourier Transform (DFT). According to the characteristics of different order harmonic, even harmonics and odd harmonics are analyzed respectively. Here, second harmonic is used to determine the spectral intensity, and third harmonic is mainly used to locate the position of spectral lines. With optimum 10 Hz frequency modulation, acetylene absorption experiments were carried out. The pump current of EDFA is 60 mA and the acetylene concentration in the gas cell is 1%. After spectra extraction, in the 1526 nm to 1537 nm wavelength range, 17 absorption lines of acetylene were achieved. The results indicated that the error of wavelength position is less than 0.1 nm and the minimum detection limit of acetylene is about 120x10^-6. It is possible to realize the recognition of measured gas type and multi-component gas detection for ICAGS system.

Using full-vector finite element method, transverse optical forces induced by strongly evanescent coupling between two identical nanofibers is theoretically investigated. It shows that anti-symmetry and symmetry modes can induce attractive and repulsive force, respectively. When light power of the symmetry (anti-symmetry) mode at 980nm wavelength is 50mW, the gap between the nanofibers with 400nm diameter nears 392nm, the repulsive force reaches maximum (11.5 pN/μm), which results in 30nm displacement at the center of 100μm-long free-standing nanofiber. Based on pump-probe scheme, a novel potential method for optical force measurement is proposed. Using Euler-Bernoulli beam equation and coupled mode theory for waveguides, the deformation impact on the splitting ratio of coupling nanofibers is also investigated. It is found that, through the deformation, the repulsive force from 0.9 to 17 pN/μm can change the splitting ratio of coupling nanofibers from 0 to 600 when coupling length of nanofibers is fixed at 100μm, the gap is 400nm and probe light is at 808nm. It shows that measuring the splitting ratio of the strongly coupling nanofibers can potentially provide a high sensitive method for measuring the optical force.

In order to increase the multiplying density of Fiber Bragg Grating (FBG) sensors, a novel FBG sensing network based on measuring point CDMA encoding technology has been developed. Furthermore, the necessary condition of measuring point CDMA code has been discussed and the measuring performances of this system have been analyzed. Simulation experiment indicates that in a spectral range of 25.5nm, this type of sensing network can arrange 41 FBG sensors and the measuring range of every sensor reaches 10 nm.

The temperature and solution concentration sensing characteristics of tilted fiber Bragg grating (TFBG) are investigated by means of theoretical analysis and experiments in this paper. It shows that the core and cladding modes exhibit nearly but not exactly the same thermal sensitivity with good linearity throughout the inquired temperature range. The dualsensitivity problem of TFBG to temperature and solution concentration is solved by calibrating every cladding mode wavelength with the core mode wavelength which is not sensitive to the solution concentration respectively to compensate the temperature effect, and this method makes thermal independent solution concentration measurement possible. It indicates that the cladding modes wavelengths linearly shift to the long wavelength direction with the increasing sucrose aqueous solution concentration, the demonstrated sensitivity is up to 5.6 pm/(g/40mL).

Fiber Bragg grating (FBG) is an important optical passive device and widely used in optical fiber communication system. The application of normal organic polymer coating FBG used in some area is limited because of its easy annealing and aging at high temperature. Employing chemical methods, we obtain certain thickness of uniform and compact surface silver layer by controlling etching conditions and reaction time. Since the interference of the external stress, the experiment result shows that the sensitivity of temperature keeps good linear response characteristic in the meanwhile. It is proved that FBG with metal silver coating effectively improved the characteristic in its sensing area.

Phase Generated Carrier (PGC) with directly Frequency Modulation (FM) is one of the most important demodulation methods for optical fiber interferometric sensor system. Previous research has confirmed that system performance using Orthogonal Demodulation Type PGC (ODT-PGC) method is determined by many parameters, such as signal phase delay, FM depth, laser intensity accompanying modulation. This article proposes a new PGC demodulation method based on Fixed Phase Delay (FPD-PGC) by 3x2 directional coupler, using second-harmonic components of two interferometric signals to demodulate. The demodulation principle of the new method is described in detail and its performances have been studied. Theoretical analysis and experimental results show that the new method combines main advantages of directional coupler method and ODT-PGC method, and eliminates, to a great extent, the impacts of FM depth, signal phase delay, intensity modulation. Signal-to-total-Harmonic Ratio (SHR) of new method increases more than 30dB compare with ODT-PGC method under the condition of intensity modulation coefficient is 0.4. Besides that, Signal to Noise Ratio (SNR) also improves significantly.

Based on low-coherence white light interferometric technology, a novel multi-path combination matching Michelson interferometer system has been proposed and demonstrated. The multi-path combination Michelson interferometer is configured by a series 2x2 fiber optic coupler connected each other. One end of the coupler array is connected with SLD light source in one port, the other port is linked with a photodiode detector. The other end of the 3dB fiber coupler array is with a coated reflective mirror in one port, the other port is terminated with a fiber collimator, and a reflective scanning mirror mounted on a translation stage and perpendicular to the fiber collimator. The scanning mirror is moving back and forth to match each optical path of the combination Michelson interferometer. In this multi-path combination Michelson interferometer, each fiber arm could be used as strain or deformation sensor. By using optical path tracking and recording technique, the quasi-distributed strain of each fiber arm can be calculated. The sensing system can be used to measure distribution strain or temperature. It has the potential in the applications of large scale smart structures health monitoring.

Third order nonlinear properties of new composite materials obtained by embedding A new type π-conjugated poly [2,1,3-benzoselenadiazole-(2,5-didodecyloxy-1,4-phenylene)ethynylene](PPE)in porous silicon are measured in 532nm. The picoseconds measurements show a significant increase of nonlinear refractive index not only with respect to the standard optical materials. The reason can be explained as follows, the Π-electron conjugation bond would be expected to have a significant effect on the ground and excited state dipole moments and electronic transition energies of the molecule and, consequently, could affect the third-order nonlinear optical property of the molecule. The result shows that it is a promising candidate for further material development and possible photonic device applications.

Ammonia, the third most important abundant nitrogen compound, is a primary alkaline gas in the atmosphere. It has strong absorption bands in the deep ultraviolet (DUV) spectral range and so can be reliably detected by the differential optical absorption spectroscopy (DOAS) technique. A portable UV-DOAS gas sensor based on multi-pass cell has been designed to detected trace gases, especially for ammonia, in the DUV spectral range, with good performance using a broad-band Deuterium source and high-sensitivity spectrometer. With the optical path as long as 20m, such a sensor could detected NH3 concentrations as low as 100ppb according to the result of in-situ measurement. Fast response time and low measurement error of this portable gas sensor could be competent for emergency monitoring.

Theoretical and experimental aspects of the extrinsic Fabry-Perot(FP) interferometric(EFPI) optical fiber sensor are studied. For a low-finesse EFPI sensor, the change of cavity length will influence the visibility of the interference fringes reflected back into the fiber. In this paper, an analysis on the fringe visibility of EFPI sensors based on the power distribution is presented. The effect that the cavity length and the source bandwidth play in the fringe visibility of EFPI sensors interrogated with a broadband light source which makes the sensor immune to source fluctuations is explored. The analysis may provide useful guidance for sensor design.

In this paper, a new method was proposed to fabricate tapered optical fiber which has strong evanescent field in the tapered region. Our system relies on a scanned high-frequency pulsed carbon dioxide laser (CO₂ laser) beam across the taper region. The optimal heating and stretching parameters were determined through a series experiments. An effective laser scanning pattern was designed to obtain a relatively uniform temperature field. Symmetrical fiber tapers with taper waist diameters of ~10-20μm, overall lengths of ~10-17mm and transmission losses of ~0.8-3dB at 1550nm were obtained. The taper profile was measured which presents a good fit with the "decaying-exponential" model. The "selfregulating" law is demonstrated, which shows the desired taper waist diameter as a function of the laser power. A refractive index sensing experiment using the tapered optical fiber is also studied to show the potential application in refractive index sensor.

In the past few years, fiber Bragg grating (FBG) sensors have attracted a lot of interest and there were number of studies on the use of FBG sensors to detect the strain of steelworks. This paper describes the strain sensors based on FBG with different package used for steelwork. Strain distribution of the steelwork is predicted through Finite element analysis. Bare FBG, FBG sensor packaged with steel sheet and resistance strain gauges are set on the same specified location of steel specimen, and load is added on the steelwork by rally machine. Strain values of the steel specimen can be caught by three kinds of sensors when load is stabilized. Then the load added on the steelwork is changed from 0KN to 50KN and back to 0KN, meanwhile the values of strain are recorded respectively. Results of three sensors are compared mutually and are all close to theoretical values provided by FEA.

Pyramid wavefront sensor (PWFS) without modulation is prevailing over one with modulation. So far how to describe measured signals of non-modulation PWFS needs deeply research. In this paper, the theory of the non-modulation PWFS is briefly presented according to wave optics. This paper analyses the existing four approaches in theory. By numerical simulation this paper further verifies the performance of four approaches under the experiment condition. The result shows that the approach with total intensity of pixels conjugate to the same spot in the pupil as signal denominator is the best choice for the non-modulation PWFS in closed-loop correction.

To measure the wave-front aberration, the Shack-Hartmann(SH) wave front sensor(WFS) is used in most adaptive optics(AO) systems. The accuracy of the centoid(Center of gravity) detecting of sub-images plays an important role in the performance of SHWFS. Normally the centriods of the point source spots are estimated to determine the local wavefront slopes by a center-of-gravity (CoG) algorithm. However the CoG algorithm suffers from several weaknesses. At first, there are few situations when a standard point source is available, such as situations with strong atmosphere disturbance and low flux. Secondly, CoG suffers significantly from CCD read-out noise. Instead of the traditional CoG, the correlation algorithm to estimate the wave-front slopes is used here, and the main characteristics of this method is analyzed. Analytical results predict this correlation approach presents better linear and robust performance. Moreover both simulation and experimental data from a point source based indoors experiment are carried out to verify the expected conclusions. The result agrees well with the simulation analysis.

In this paper, the characteristics of the LPG with thin film coating are analyzed theoretically by using the optical couple-mode theory and cylindrical four-layer waveguide model. The influences of the refractive index and thickness of film overlay on the sensitivity of LPG are analyzed in detail. By choosing properly the thickness and refractive index of the thin-film overlay, the sensitivity of the LPG can be enhanced significantly. In order to verify the theoretical analysis and enhance the sensitivity of LPG to humidity, hydrogel is chosen as coating material. The characteristics on the hydrogel coated long period grating are investigated experimentally. The transmission spectral response of hydrogel coated LPG to relative humidity is measured. It shows that the resonant wavelength and the amplitude of attenuation bands are high sensitive to relative humidity when RH is above 50%RH.

By investigation of the theoretical model of fiber microbend sensor, and derivative of the basic function of microbend with respect to applied external force F then Young's modulus E, we get an expression of sensor's output signal as a function of E which shows that the output of the microbend sensor decreases with the Young's modulus of the gripper increasing, and the change is nonlinear. To verify the accuracy of the theoretical derivation, we design and make four optical fiber microbend grippers of different materials, including stainless steel, Polyvinyl Chloride (PVC), polypropylene (PPR) and bamboo, with the same geometric parameters of grippers such as a mechanical period derived for the maximal sensitivity from the well-known microbend interval equation, and carry out the demonstration experiments under the same initial testing conditions. The initial testing condition has been adjusted during the process of manufacturing and installing the fiber microbend gripper. The experimental data based on our design testing systems showed that the outputs of the microbend sensors match our theoretical simulation curves well to the applied external force F. The conclusion might be useful for future reference of microbend strain sensors design.

The purpose of the fiber micro-drop analyzing technique is to measure the characteristics of liquids using optical methods. The fiber fingerprint drop trace (FFDT) is a curve of light intensity vs. time. This curve indicates the forming, growing and dripping processes of the liquid drops. A pair of fibers was used to monitor the dripping process. The FFDTs are acquired and analyzed by a computer. Different liquid samples of many kinds of preparation of Chinese traditional medicines were tested by using the fiber micro-drop sensor in the experiments. The FFDTs of preparation of Chinese traditional medicines with different concentrations were analyzed in different ways. Considering the characters of the FFDTs, a novel method is proposed to measure the different preparation of Chinese traditional medicines and its concentration based on the corresponding relationship of FFDTs and the physical and chemical parameters of the liquids.

Fibers in the optical fiber sensors would react with water and hydrogen in permanent downhole measurement under the high temperature and pressure. This reaction would change the absorption loss of the fibers, which would affect the reliability of the measurement system. To analyze this problem, the course of hydroxyl penetrating through fibers was investigated. The source of penetrating hydroxyl was discussed. The penetration changes the chemical bond combination inner the fibers, which causes the increase of the absorption loss and the reduction of useful life of the fibers. The results show that at the wavelength of 1.38μm, when the content of the hydroxyl group is about 0.0001, the absorption loss can reach 33dB/km. The analyses also point out that carbon-coated fiber could increase the static fatigue resistance parameter, thus increasing the useful life of the fibers exponentially.

A novel optical fiber humidity sensor using polyvinylidene fluoride (PVDF) as sensitive material was proposed in this paper. Three-layer coating was deposited on the end-face of optical fiber, which constructs an extrinsic Fabry-Perot (F-P) interference structure. Ag layer deposited by DC magnetron sputtering was used as mirror layer in the F-P interference structure. PVDF layer was realized with Czochralski method as F-P cavity. Simulation was performed using data fitting to analysis the relevant parameters on sensor performance. Experimental result shows the interference fringe shifts to longer wavelength when relative humidity increases. The fringe shifted 2.4nm with a good linearity response when relative humidity increases from 11% to 97%. The linearity of interference fringe shift to relative humidity was 0.98415, the response time was less than 1min.

A strain sensor based on cladding mode resonance of optical double-cladding fiber (DCF) was proposed and experimentally demonstrated. The sensor head was fabricated by splicing a section of DCF into a standard single mode fiber (SMF). Attributed to the thin thickness of the inner cladding, the core mode can be coupled with cladding modes which generatess a strong resonant spectrum at the phase-matching wavelength. When the DCF sensor is applied an axial strain, the refractive index of the DCF decreases due to the photoelastic effect. According to the coupled mode theory, the phase-matching wavelength will shift to a shorter wavelength. By detecting the resonant spectrum variation, the stain sensor can be realized. The strain sensitivity was achieved as -2.87 pm με over 800με measurement range with good repeatability. With the simple configuration and attractive performance, the specialty DCF strain sensor can be explored for wide sensing applications.

A fiber distributed feedback laser accelerometer base on the double flexure strips structure is designed and experimentally studied. In this paper, the vibration response of this double flexure strips structure is theoretically analyzed and simulated. The ripple response of the proposed sensor is less than 1dB from 50 Hz to 350 Hz. The experimental results show that the sensor has a higher sensitivity of 1591rad/g at 400Hz by introducing a 3x3 coupler combining with an unbalanced Mach-Zehnder fiber interferometer demodulator. Signal-to-Noise and cross-sensitivity coefficient of the sensor signal are about 43 dB and 10 dB respectively.

MEMS gyro is used in inertial measuring fields more and more widely, but random drift is considered as an important error restricting the precision of it. Establishing the proper models closed to actual state of movement and random drift, and designing a kind of effective filter are available to enhance the precision of the MEMS gyro. The dynamic model of angle movement is studied, the ARMA model describing random drift is established based on time series analysis method, and a modified self-adapted Kalman filter is designed for the signal processing. Finally, the random drift is distinguished and analyzed clearly by Allan variance. It is included that the above method can effectively eliminate the random drift and improve the precision of MEMS gyro.

Two type of output spectrum profile, flat and gauss profile were realized with gain flatten filter and edge filter respectively. For high performance fiber optic gyroscope application, a vary parameters control technology was taken and the less than 0.5 ppm/ °C mean wavelength stability and less than 1% output power stability were achieved within operation temperature -45 °C - +70 °C .To developing radiation-resistance broadband source, the erbium-doped fiber radiation characteristic was studied experimentally and the super-fluorescent fiber source configuration parameters and pump laser diode power were optimized. The radiation-resistance super-fluorescent fiber source module was made. Experimental test shows that two type of SFS, include gauss and flat profile spectrum, can stand against more than 50Krad(Si) radiation dose.

The temperature or/and strain measurement accuracy, resolution and response of distributed optical fiber sensors based on Rayleigh, Raman and Brillouin scattering are mainly limited by their weak signals and low signal-noise ratio (SNR). To improve the SNR and response characteristic simultaneity, the wavelet transform de-noising technology was introduced to distributed optical fiber sensor system. The mother wavelet and the processing of thresholds were optimized in order to get better SNR and minimize the impact to signal response. A Raman scattering distributed optical fiber sensing experimental system was set and the signal process arithmetic was realized. Experimental tests indicate that wavelet de-noising method can notably improve SNR and guarantee the spatial resolution simultaneously. Final contrast tests suggest that not only the temperature resolution was improved by more than 50%, but also the measurement accuracy and period were improved greatly.

A novel optical fiber sensor for simultaneous measurement of pressure and surrounding refractive index (RI) based on long period gratings (LPGs) is proposed and demonstrated. This device consists of two LPGs with different wavelengths, one of them is shielded from the environment, therefore, is insensitive with surrounding RI. Since the resonant peaks of these two LPGs change differently, the simultaneous measurement has been done. The experimental results show that the device has a good performance in measurement.

Perception of different color contrast stimuli was studied in the presence of light scattering in a fog chamber in Clermont-Ferrand and in laboratory conditions where light scattering of similar levels was obtained. Blue (shortest wavelength) light is scattered in fog to the greatest extent, causing deterioration of vision quality especially for the monochromatic blue stimuli. We have done spectral measurements of the light source in different density fog conditions and no spectral changes were found produced by the fog. Psychophysical measurements of the acuity in fog were done for two subjects with optotypes analyzed for red and blue stimuli.

We describe a method for measuring and aligning phase parameters with Zernike polynomials in large segmented-mirror telescope system. Numerical model is developed to establish the dependence of tip-tilt phase parameters on the polynomial coefficients C₁ and C₂ and know the real displacement direction though the measurement and calculation of Zernike polynomials. Its performance is analytically examined in detail and some experimental results demonstrating its effectiveness are also given. This method extremely simplified the segment phase adjustment process to a certainty. The measurement result proved that the tilt is 15λ and the tip is 7λ (λ=633nm), showing that the precision is about to nanometer level.