This PDF file contains the front matter associated with SPIE Proceedings Volume 6830, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We report on the temperature response of FBGs recorded in pure PMMA and TOPAS holey fibers. The gratings are fabricated for operational use at near IR wavelengths, using a phase mask and a cw He-Cd laser operating at 325nm. The room temperature grating response is non-linear and characterized by quadratic behavior for temperatures from room temperature to the glass transition temperature, and this permanent change is affected by the thermal history of the gratings. We also report the first FBG inscription in microstructured polymer optical fibers fabricated from TOPAS. This material is fully polymerized and has very low moisture absorption, leading to very good fiber drawing properties. Furthermore, although TOPAS is chemically inert and bio-molecules do not readily bind to its surface, treatment with Antraquinon and subsequent UV activation allows sensing molecules to be deposited in well defined spatial locations. When combined with grating technology this provides considerable potential for label-free bio-sensing.

A highly sensitive liquid-level sensor based on etched fiber Bragg grating is proposed and demonstrated. The fiber Bragg grating is etched to enhance the sensitivity to the refractive index of liquid, when a portion of etched fiber Bragg grating is immersed in the liquid, the original single transmission dip splits into two transmission dips because of the fiber Bragg grating spectrum is affected by the fraction of the length of the etched fiber Bragg grating that is surrounded by the liquid. By measuring the transmission dips variations, the liquid level can be measured. The experiments show that for a liquid level variation of 24mm, the transmission dip difference changes about 32dB. Also in the linear region, a high liquid level sensitivity of 2.56dB/mm is achieved.

An in-line fibre ring cavity is fabricated by writing two blazed gratings next to each other to form a Fabry Perot cavity. A visibility of fringes as good as 0.032 in the reflection spectrum and 0.76 for transmission is obtained for the interference between the forward propagating guided mode and the reverse propagating ghost mode of the blazed grating. The ability to measure the external refractive index and the variability of this response with cavity length is demonstrated.

Bending characteristics of long-period gratings (LPGs) written in fiber with parabolic-index cladding are investigated experimentally. The fiber has a uniform outer cladding and an inner cladding, where the refractive index decreases quadratically with radius. A recent theoretical analysis has shown that these LPGs can be highly insensitive to bending. A very small bend-induced wavelength shift of the attenuation band of only 5 nm was predicted for an LPG bent with a uniform curvature of 100 m^-1. Experiments to prove the predicted bend insensitivity are done with LPGs written with a CO₂ laser at one-side and three-side laser irradiation of the fiber. The LPG is bent in an arrangement, where the curvature is maximum in the LPG's center and decreases linearly along the bent LPG in both directions. Bend-induced wavelength shifts of an attenuation band appearing at about 1560 nm and attributed to coupling between the fiber modes LP₀₁ and LP₀₂, are examined for four rotational orientations of the LPG inscribed at three-side laser irradiation. The largest shift of 0.46 nm is obtained for a maximum curvature (in the middle of the LPG) of 11.6 m^-1, (or average curvature of 5.8 nm^-1) corresponding to the largest deflection applied on the LPG in the experiments. The depths of the bands of the above LPG at the -5.5-dB level are observed to vary by less than 0.3 dB over the whole range of applied curvatures.

Various Moiré Long Period Gratings are fabricated and their thermal properties are measured. The occurrence of an anomalous switching effect between two thermal response curves is noted to occur at a certain wavelength. A deviation between them by as much as 1nm is observed. As the effect is stable and repeatable it offers the potential for various novel applications in the fields of sensing and optical logic.

A current sensor array which consists of tunable fiber laser, Giant Magnetostrictive Material (GMM) and fiber grating is presented. The long-haul experiment is operated on the basis of current sensor unit about 21km. In general, the results of the design of the system is credible and qualified for the designing demand. And then a current sensor array is composed of four current sensor units in 21km long-haul. The sensing properties of the wavelength divided multiplex (WDM) and time divided multiplex (TDM) is demonstrated. The wavelength resolution of the measurements is 0.002 nm and current resolution is 6.55mA, due to the high sensitivity photo detection system. While the work current go up from 1200mA to2300mA, Sensitivity of the wavelength will be maximum.

We develop a numerical modeling of the multi-channel waveguide-based surface plasmon resonance sensor based on the rigorous coupled-wave analysis. The cascaded structure which consists of elementary surface plasmon resonance sensors with different resonance wavelengths can be used for simultaneous sensing of change in surrounding dielectric constants. The method to anticipate the center wavelength of resonance is adressed and its physical underlying principle is discussed with respect to the mode distribution and phase matching condition. A few simulations are provided for validating our model and analysis.

One important advantage of interferometric optical fiber sensor is high sensitivity. The development of the interferometric optical fiber sensor is partly restricted with the demodulating technique. Because of advantages such as high sensitivity, high dynamic range, and good linearity, PGC (Phase Generated Carrier) demodulating scheme is widely applied for interferometric optical fiber sensor now. In this paper, an arctangent approach of the PGC demodulating scheme is introduced. CORDIC (Coordinate Rotation Digital Computer) algorithm is used to realize the arctangent function. CORDIC algorithm is a method for computing elementary functions using minimal hardware such as shifts, adds/subs and compares. CORDIC algorithm works by rotating the coordinate system through constant angles until the angle is reduces to zero. The angle offsets are selected such that the operations on X and Y are only shifts and adds. This method will lead in less complexity and higher accuracy. Since digital signal processing technology has achieved great development, especially the appearances of high speed processors such as FPGA and DSP, PGC demodulating scheme based on CORDIC algorithm is implemented conveniently. The experiments are carried out to verify the PGC demodulating scheme based on CORDIC algorithm.

This paper, for the first time to the best of our knowledge, presents a novel fiber-optic refractive-index sensor which is based on an intrinsic Fabry-Perot interferometer (IFPI) formed by a section of endlessly single-mode photonic crystal fiber (EPCF) and conventional single-mode fiber. Such an IFPI sensor has the advantages of easy fabrication, low joint and transmission losses, low-cost and good fringe visibility due to the use of the EPCF. Simultaneous measurement of refractive index (RI) and temperature can be realized by determination of the cavity length change and the fringe visibility of such a PCF-based IFPI, respectively. In addition, it is found that the fringe visibility of the IFPI is insensitive to temperature change, providing a practical way to measure refractive index with self temperature compensation. Such a miniature fiber-optic sensor is demonstrated for the measurement of the refractive index change of glycerin solution by measuring its fringe visibility change solely.

We derive a generalized expression based on a three-dimensional (3-D) model to fully describe the dependence of the nonreciprocity in a fiber coil caused by temperature gradient along the axial, radial, and circumferential directions respectively. We use the finite element analysis method to numerically solve the partial differential equations describing heat transfer in the fiber coil and obtain the rate and angular errors induced by the thermal transient effect with a better accuracy. We show that the 3-D model can describe the thermal transient effects induced by both the symmetrical and asymmetrical temperature gradients, which is not possible using the traditional two-dimensional model. Finally, we validate the ability of the 3-D model for predicting the thermal transient behavior in the fiber coil by comparing numerical and experimental results. The 3-D model proves useful for the development of a testing system capable of characterizing symmetrical and asymmetrical temperature transient effects in the fiber gyro coil.

In this paper a novel distributed fiber optic crack sensor with polymer encapsulation based on optical time domain reflectometer (OTDR) is presented. The sensor head includes two layers of polymer and a bare fiber embedded in them. The crack induced deformation in the sensor head will result in the bend loss in the fiber. Utilizing the OTDR measurement, the position and the size of the crack can be determined. Two types of fiber arrangement are introduced in this paper. Experiment was carried out to evaluate the performance of the distributed fiber optic crack sensor. The primary results show that the fiber optic crack sensor has good linearity between the bend loss and the crack open size. The crack size resolution is better than 1mm.

A new type of distributed optic-fiber sensing system based on Sagnac/Mach-Zehnder has vast prospects in early warning of oil and gas pipeline sabotage, so it is necessary to study the problem of degradation of polarization state which interrupts the application of the sensing system. Firstly, a model of the impacts of polarization state on power transmission coefficient is established in terms of Jones matrix method. With the existence of birefringence, simulations are respectively made: the influence of the changes of equivalent birefringence element parameters on the output signals of the Sagnac interference system, and with the different angles of polarized light, the interruption of Mach-Zehnder interferometer in the response of output to the outside world. A conclusion is drew out: the existence of birefringence will not only lead sensing system to misjudge the outside world's behavior, but it will also affect the interference output signal's phase, and then affect the positioning accuracy. At last, the adjustment of fiber mechanical polarization controller to the system polarization state is selected and polarization control program which uses phase modulation method to evaluate the system-polarization is designed.

The residual axial strain induced in the cabled fiber is a vital factor to evaluate the reliability of optical fiber cables. However, little is known about the thermal effect on the fiber residual strain, especially on the particular short section of the fiber. In order to precisely determine the thermal effects on fiber residual strain of optical cables, a measurement method based on Brillouin Optical Time-Domain Reflectometry (BOTDR) system is proposed. Thermal characteristics of fiber residual strain of optical fiber cables are investigated theoretically and experimentally. Measurements of the residual strain in particular short section of fiber are made with the distributed fiber sensing system based on BOTDR. Experimental results for a double-coated fiber in loose structure cable are in good agreement with those predicted from the theory. It has been found that the fiber residual strain increases linearly with the decrease of the temperature in the range from 50°C to -50°C.

The design and field test of a perimeter security system based on fiber optic disturbance sensor was described. The system consisted of fiber optic disturbance sensor and control computer. The fiber optic disturbance sensor was in Mach-Zehnder interferometer configuration using single mode fiber cable, which made the system relatively low cost. A digital Phase Generated Carrier (PGC) demodulation technique was used to eliminate phase drifts in the interferometric sensor. The demodulator was based on Field Programmable Gate Array(FPGA) and Digital Signal Processor(DSP). A prototype system with 1Km sensing cable was constructed and tested. The sensing cable was bound on the fence to detect disturbance generated by intruder. The test result verified that this sensor was sensitive to intrusion behavior. Typical disturbance signal was recorded when intrusion behavior was going on. There was obvious characteristic in the recorded signal. Intrusion behavior generated non-stable random signal, which had many amplitude peaks. And the frequency was below 500Hz. This was helpful for recognition algorithms development. Wind in the test field also generated low frequency background noise and increased recognizing difficulties.

A nonlinearity correction using ellipse fitting technique based on orthogonal polarized laser interferometer is proposed in this paper. In this paper, characteristics of four-channel output signals based on polarized Michelson laser interferometer are studied. The orthogonal signal's non-orthogonal error which is caused by temperature disturbance and low frequency vibration noise is compensated. Besides, a new algorithm of demodulating small phase signal is proposed. Low frequency vibration signal demodulation system based on DSP technique is constructed. It proposed an ellipse fitting algorithm based on Least-squares theory. This algorithm can achieve correction error of less than ±0.3%. System's real-time measurement capability and its resolution can be improved.

Telomerase, a ribonucleoprotein enzyme that adds telomeric repeats to the 3'end of chromosomal DNA for maintaining chromosomal integrity and stability. This strong association of telomerase activity with tumors establishing it is the most widespread cancer marker. A number of assays based on the polymerase chain reaction (PCR) have been developed for the evaluation of telomerase activity. However, those methods require gel electrophoresis and some staining procedures. We developed an electrochemiluminescent (ECL) sensor for the measuring of telomerase activity to overcome these problems such as troublesome post-PCR procedures and semi-quantitative assessment in the conventional method. In this assay 5'-biotinylated telomerase synthesis (TS) primer serve as the substrate for the extension of telomeric repeats under telomerase. The extension products were amplified with this TS primer and a tris-(2'2'-bipyridyl) ruthenium (TBR)-labeled reversed primer. The amplified products was separated and enriched in the surface of electrode by streptavidin-coated magnetic beads, and detected by measuring the ECL signals of the TBR labeled. Measuring telomerase activity use the sensor is easy, sensitive, rapid, and applicable to quantitative analysis, should be clinically useful for the detection and monitoring of telomerase activity.

A novel optical fiber relative humidity(RH) sensor was proposed in this paper based on fiber evanescent wave coupling. Sol-gel material with porous microstructure as water molecules sensitivity film was dip-coated upon coupling region surface. Visibility calculated from output optical powers of the coupler sensor was taken to show the sensitivity to relative humility. From the experimental results, with increasing relative humidity ranged from 25% to 95%, the visibility decreased in a good linear manner. And the sensitivity was approximate 0.132/RH%. Due to simple technique and low lost of the fiber coupler relative humidity sensor, it will be applied widely.

A system that accurately positions a 35mm film camera or HDTV sensor at the infinity focus image plane of a large-aperture tracking telescope in the field is described. A beam of collimated laser light is scanned across the entrance pupil of the telescope while tracking the movement of the centroid of the image formed at the sensor. In the case of an HDTV camera, the electronic signal is sampled directly, whereas for the 35mm film camera a secondary re-imaging system is employed to capture diffusely scattered light from the film surface.

With maturation of UAV (Unmanned Aerial Vehicle) key techniques, the UAV aviation is more stable than before. That shows us the possibility of reconnaissance in atrocious environment. Here the structure of an UAV remote sensing platform is given out first. Then the control system modules of aerial remote sensing and their functions with each realization are discussed in detail. The experiments show that the system can satisfy the needs for aerial remote sensing task.

This paper presents a PGC interrogation scheme when a three-mode DBR fiber laser is used for fiber optic interferometer. By carefully adjusting the path difference of interferometer, ▵L, a stable interferential signal can be generated when ▵L is 2g times of DBR resonator length, where g is an integer. When acoustic signal acts on the interferometer, the PGC demodulation result is in consistent with that obtained with a single mode, high coherent fiber laser.

In this paper, the glass microsphere co-doped Er³⁺/Yb³⁺ was fabricated. Many regularly spaced, sharp peaks appeared in the emission spectra of the glass microspere. We report the laser power induce the spectral shift of the whispering-gallery-modes [WGMs] of a glass sphere. The laser power dependence of the WGMs spectral position is about 0.0252nm/mW under 976nm excitation. Maybe, the glass microsphere can be used as a temperature sensor.

A novel weigh-in-motion (WIM) system used for high way is developed based on Chirped fiber Bragg gratings (CFBG) in this paper. The WIM system consists of four CFBG pressure sensors, each of which contains a couple of CFBG. The sensor can directly output optical intensity signal, so the postprocessor instrument is simple and cheap instead of expensive wavelength demodulation apparatus. Theoretical and experimental results indicate that output optical intensity of the sensor is linearly proportional to the pressure, and the linearity and the repeated error can respectively reach to 0.9997 and 0.05%FS. We have also exceeded series experiments with several kinds of automobile with different velocity, and received good results of relative error below 5%.

A theoretical analysis of multiple scattering is undertaken. The effect it has upon systems that do not take multiple scattering events or spectral shadowing into account through their signal processing routines is examined. An exact first order compensation scheme and higher order non-exact compensation schemes are developed. A comparison is made between the system performance that is obtained from the uncorrected, first-order corrected and higher-order corrected systems. The comparison makes use of a worst-case time-independent scenario.

Wavelength encoding sensors, such as fiber Bragg grating, have the advantage of strong antijamming ability. However, the wavelength encoding signal is usually converted into electric intensity signal by demodulators in most measurements. The intensity signal is easy to be disturbed by environmental factors, so the advantage of wavelength encoding fails due to the instable intensity demodulation. In this paper, a novel wavelength demodulating method is presented. This method demodulates the wavelength encoding signal directly by means of counting using a Sagnac interferometer with birefringent fiber without the encoding conversion from wavelength to intensity. Through the interferometer, the changed wavelength signal from sensor becomes the kind of output light, the intensity of which is changed with wavelength periodically. The intensity can easy be disturbed, but its period is very stable. In other words, the change of wavelength in one intensity period is stable. With this character, we count the number when the rising edge and falling edge of intensity appear, and then calculate the accurate change of wavelength signal. In experiment, we get the 0.01 nm wavelength resolution by use of a Sagnac interferometer with 200 meter birefringent fiber. It can be proved that the intensity frequency (the reciprocal of intensity period) changed with wavelength is proportional to the length of birefringent fiber. The length is fixed, the frequency is determined. For farther increasing the wavelength resolution, it is only necessary to increase the length of birefringent fiber. The wavelength demodulator by counting method has high stability and high precision.

It is well known that as a measurement device, Sagnac fiber interferometer has the advantages of high measuring sensibility and strong antijamming ability. However, it is precisely because of the high sensibility, the measured change range of sensed quantities is usually very small. And also because of the strong antijamming ability, the fiber of Sagnac interferometer can not be used as a sensor. The reason is that the sensed signal well be eliminated by the signal cancellation effect between the two directions in Sagnac interferometer like the disturbance signal. This paper presents a novel Sagnac fiber sensor. It is added two devices into the common Sagnac fiber loop, one is the phase compression device and another is the birefringent fiber sensor. The phase compression device consists of a time delay fiber and a piezoelectic ceramic twisted around by Sagnac fiber. This device can realize the phase compression by which the measured range of sensed quantities is widely extended. The birefringent fiber sensor consists of a short section of high birefringent fiber. The method of adding the birefringent fiber sensor is selecting suitable position on Sagnac fiber loop and breaking off the fiber, then melting and linking the two break surfaces with the short section of high birefringent fiber. Not like the common fiber, there is not cancellation effect on the birefringent fiber. So the Sagnac interferometer can become a sensor. This kind of Sagnac fiber sensor has the advantages of high measuring precision, wide measured range, strong antijamming ability and simple structure.

A multiplexing technique using amplitude-modulated chirped fibre Bragg gratings (AMCFBGs) is presented. This technique realises the multiplexing of spectrally overlapped AMCFBGs with identical centre Bragg wavelength and bandwidth. Since it is fully compatible with the wavelength division multiplexing scheme, the number of gratings that can be multiplexed can be increased by several times. The discrete wavelet transform is used to demodulate such multiplexed signal. A wavelet denoising technique is applied to the multiplexed signal in conjunction with the demodulation. Strain measurements are performed to experimentally demonstrate the feasibility of this multiplexing technique. The absolute error and crosstalk are measured. An application to simultaneous two-parameter sensing is also demonstrated.

A novel Michelson interferometric fiber-optic hydrophone with a mechanical anti-aliasing acoustic filter, which consists of a two-hole cylindrical Helmholtz resonator, has been manufactured and tested. Experimental results show that this new fiber-optic hydrophone has a function of acoustic low-pass filtering. The low frequency sensitivity, as determined by the fiber interferometer and the sensing mandrel, is about -159dB re 1rad/μPa. The frequency response has a break point near 1200Hz and a measured roll-off of 50dB/octave. The fiber-optic hydrophone is a prototype device for a class of sensors that used to eliminate aliasing in the future sonar systems. To our knowledge, this is the first time that such a fiber-optic hydrophone has been reported.

In this work, the acceleration responsivity of the optical-fiber air-backed mandrel hydrophone is proposed and investigated both analytically and experimentally. The acceleration responsivity is a significant index of the hydrophone, and it would be a serious noise source of pressure phase sensitivity of the fiber-optic hydrophone in high vibration environments. The three-dimensional quazistatically theoretical model of the hydrophone is created and the acceleration responsivity of the hydrophone is analyzed. On the basis of the analyses of the parameters of the theoretical model, main restrictively factors and the improved methods are obtained. According to general format which is proposed, certain structures of the mandrel fiber-optic hydrophone is produced with determined parameters, and the acceleration responses validate our theory model. The theoretical and experimental treatment give a set of guidelines, which should be followed in order to minimize the acceleration responsivity of the fiber-optic mandrel hydrophone, and the symmetrical structure could be applied to reduce the acceleration noises greatly. The hydrophone could be designed to achieve the required performances according to the model created above.

This paper describes the ground target detection, classification and sensor fusion problems in distributed fiber seismic sensor network. Compared with conventional piezoelectric seismic sensor used in UGS, fiber optic sensor has advantages of high sensitivity and resistance to electromagnetic disturbance. We have developed a fiber seismic sensor network for target detection and classification. However, ground target recognition based on seismic sensor is a very challenging problem because of the non-stationary characteristic of seismic signal and complicated real life application environment. To solve these dificulties, we study robust feature extraction and classification algorithms adapted to fiber sensor network. An united multi-feature (UMF) method is used. An adaptive threshold detection algorithm is proposed to minimize the false alarm rate. Three kinds of targets comprise personnel, wheeled vehicle and tracked vehicle are concerned in the system. The classification simulation result shows that the SVM classifier outperforms the GMM and BPNN. The sensor fusion method based on D-S evidence theory is discussed to fully utilize information of fiber sensor array and improve overall performance of the system. A field experiment is organized to test the performance of fiber sensor network and gather real signal of targets for classification testing.

A resonant fiber-optic sensor using a general ring fiber is proposed. A frequency sweep sinusoidal intensity modulated laser beam is injection locked to the ring fiber sensor using a fiber coupler of low coupling coefficient. The ring fiber is a resonant ring as well as an extracted carrier. In respect that the resonant ring of difference length has difference resonant frequency, the systems operating in the length range 0.6-2 meters and resonant frequency range 100-300MHz, frequency division multiplexing has been used in these sensor systems. Demodulation was achieved by using frequency tracking demodulator that uniform amplify signals in large bandwidth and a narrow band filter in it, so that it has a high signal to noise rate(SNR). According to the experiments with a general ring fiber, the method is very easy and inexpensive to implement, demodulation linearity over 1 decades and minimum relative variation detection ∼0.1% attained. The ring fiber sensors have certain advantages that include high sensitivity, large bandwidth, and ease in implementing multiplexed or distributed sensors. Strain, temperature and pressure are the most appropriate measurands in the systems.

In this paper, the FFT (Fast Fourier Transform) demodulation method conbined with CZT(Chirp Z-Translation) is adopted here for Fabry-Perot pressure sensors and its principle and error are analyzed theoretically. CZT is a kind of DFT (Discrete Fourier Transform) in some special condition and it is usually used to thicken the frequency spectrum. CZT can do nothing to reduce the error from FFT and itself may induce error but the error here from FFT and CZT will influence the demodulation resolution a little. In the simulation, cavity lengthes from 397 to 403 μm with the space of 0.5 μm are simulated and the result shows that the relative error of this new method is less than 0.01% and the maximum absolute error is less than 0.05 μm. In the experiment of the demodulation of the MEMS Fabry-Perot pressure sensor, whose metrical range is from 0 to 3 Mpa, its resolution reaches 0.01 MPa, its linearity between the length of the cavity and pressure achieves 0.99316 and the standard deviation between measured pressures and real pressures is less than 0.005 Mpa. By the experiment we can see that this new method adapts to the practice demand with its higher resolution and less calculational quantity.

Based on the transfer matrix method, the reflection spectra of strained chirped fiber gratings are analyzed theoretically. Chirped fiber gratings are fabricated by etching uniform FBGs with HF. The cross section of the chirped FBG has a gradient variation along the axis. The full width at half maximum of the refection spectra of the chirped fiber grating can reach 0.4-0.75nm. When axial stress is applied on the chirped FBG, the bandwidth can reach 5nm. The sensitivity of the bandwidth to stress can achieved 20% higher than that of uniform fiber Bragg gratings. The relationship of the bandwidth and the imposed force, as well as the one between the reflection power and the force, derived from the coupled mode theory, will also be tested in the experiments, which has been shown in this paper.

This paper describes a high-performance multiplexed vibration sensor system using fiber lasers. A serial vibration sensor array consists of four short cavity fiber lasers. The system employs a single, polarization-insensitive, unbalanced Michelson interferometer to translate individual laser wavelength shifts induced by vibration signals into interferometer phase shifts. A dense wavelength division demultiplexor (DWDM) with high channel isolation is inserted to demultiplex each laser signal as a wavelength filter. Finally, a digital phase demodulator based on the phase generated carrier technique is used to achieve high-resolution interrogation. Experimental results show that no observable crosstalk is measured on the output channels, and the minimal detectable acceleration of this system is ~200ng/&sqrt;Hz at 250Hz, which is fundamentally limited by the frequency noise of the lasers.

Two-core fiber is a specially designed fiber which contains a pair of parallel fiber core surrounding a cladding with diameter 125μm. A multi-parameters measurement technique that uses a two-core fiber as the sensing element has been proposed and demonstrated in this paper. The theory and the structure design are also introduced. The two-core fiber acts as a two-beam interferometer, in which phase differences is a function of curvature, and the twisting angle in the plane containing the cores results in the shift of the far-field interferometric fringe pattern. This sensor can be used to inspect the structural health monitoring, the measuring angle and the distinguishing direction. Compared to the traditional multi-beam interferometer, this sensor has the such characteristics as small size, good interference, high definition and steady fringe pattern. It does not need considering the effect of the environment temperature. A low-coherence laser diode at wavelength 650nm illuminating the two-cores and the interferogram pattern in the far-field is recorded by a CCD camera. The model of two-core fiber sensor has been established theoretically. The relationship between the far-field fringe pattern intensity distribution and the changes due to the radius of the curvature and the twisting angle are given, and the experimental results also confirmed this.

A novel fibre-optic methane detection system was proposed, which involved sampled fibre grating and improved differential absorption detection technique. By this method, near-infrared equal-spaced multi absorption line of methane was detected simultaneously, and that gas weak absorption detection theory was developed. Using the comb shaped filter characteristic of sampled fibre grating, R2, R3 and R4 line of molecule absorption spectrum in 2ν 3 overtone band around 1.66μm was measured at one time. Two sampled fibre gratings of same type were used to fulfill the task of difference absorption detection. One sampled grating worked as measure grating with its reflection spectrum corresponding to the absorption line. The other grating worked as reference grating with its reflection spectrum deviate from that of measure grating to some extent. Chirped fibre grating with its central wavelength around R3 was adopted as optical band-pass filter. The light power of the three absorption line and the three reference wavelength was detected alternately by PIN PD at the same time. So that difference absorption detection was achieved. The effect of light source instability was avoided by ratio treatment. The validity of the system was verified by experiments.

In this paper, a packaged erbium-doped fiber amplifier (EDFA) is integrated into a fiber ring to form an erbium-doped fiber ring (EDFR) laser which is applied to measure the particle size based on the self-mixing Doppler effect. A detailed analysis is addressed to introduce the measurement principle, and the obtained results demonstrate that the diameter of the Brownian particles in water can be measured by detect the variations of the intensity and frequency of the fiber laser. This technique can be used in biology, process engineering and chemistry.

Many chemical sensors based on fluorescence spectroscopy have been reported in applications, ranging from biomedical and environmental monitoring to industrial process control. In these diverse applications, the analyte can be probed directly, by measuring its intrinsic absorption, or by incorporating some transduction mechanism such as reagent chemistry to enhance sensitivity and selectivity. Hydrogen Peroxide is a colorless liquid. It is a common oxidizing and bleaching agent. It plays an important role in High Power Laser such as Chemical Oxygen Iodine Laser (COIL). As it is on the Hazardous substance list and on the special health hazard substance list, detection of Hydrogen Peroxide is of great importance. In the present study the detection of hydrogen Peroxide is by fluorescence quenching of laser grade dye Rhodamine B. Estimation of rate constant of the bimolecular quenching reaction is made.

The techniques used in dynamic detection of airfield lighting intensity are introduced in this paper. These techniques can take place of the old method of checking all manually, and the system can detect the lights intensity online quickly and exactly, so as to find out the light faults and ensure the safety of planes taking off, landing and slipping. The system uses a car with a string of sensors which have been cosine calibrated and v(λ) calibrated to detect the light intensity. When the car is moving, the sensors can detect the lights' horizontal section. To accurately measure the distance from the measured aerodrome assistance light to the moving car, and then calculate the light intensity and protract the iso-candela curve, the Doppler ranging radar system is used. To guarantee the dependability of the system and the measurement precision, a video monitoring and guiding system is used to assure the car to run along the airfield lights line, then light orientation sensors are used to eliminate the radar's cumulating errors. The experiment indicates that this system is feasible and has high detecting precision.

Flattened ASE fiber sources with C+L bandwidth(1520-1620nm) are attractive. Long period fiber gratings (LPFG) have the characteristics of band-stopped, which can be used to flatten the spectrum of amplified spontaneous emission (ASE) light source. In this paper, spectrum flattening of ASE light source covering C-band and L-band based on a long period fiber grating is studied. As a flattening filter, LPFG is often placed in the end of the output port. The results in this paper show that the placed position of LPFG has great influence on the spectrum flattening of ASE light source. Output spectrum measured of filtered ASE source with the LPFG at different position is given, and the detailed theoretical analysis to explain the experimental results is followed. In the dual-stage double-pass structure, based on a long period fiber grating and two 980 nm high power semiconductor lasers, high power and ultra bandwidth ASE fiber source has been gained. The source has a bandwidth of 77 nm (1525.5 ~1602.5 nm) with ±1.6 dB ripple and 42 mw of output power.

As novel passive optical components, fiber gratings have a comprehensive prospect in optical communication and sensing systems, due to their excellent optical properties. Blazed fiber Bragg grating, an important member of fiber gratings, because of its special structure, not only has all properties of fiber Bragg grating, but also has its own unique properties. With the fiber sensitivity enhanced and the technology of fabrication fiber grating improved, blazed fiber Bragg grating with an excellent character comes true, which have been used in the area of gain flatten, sensing system and wavelength demodulation. The sensing theory of blazed fiber Bragg grating is presented in the paper. Theoretical and Experimental research on its temperature sensing characteristic, strain sensing characteristic have been taken. The blazed fiber Bragg grating has the same temperature sensing and strain sensing characteristic as fiber Bragg grating. The temperature sensitivity experiments of the grating have been studied. By packaging fiber gratings with a special type of polymer, the experiments indicate that the temperature sensitivity to seven times.

The chemical sensing principle based on Fiber Bragg Grating (FBG) is presented. By deriving the relation between effective core index and surrounding index of etched FBG, the relation between Bragg wavelength and concentration of chemical solutions is analyzed, which is demonstrated in the experiment by measuring propylene glycol solutions. The factors influencing the sensitivity of chemical sensing is investigated. The results show that, the sensitivity of the Bragg wavelength of FBGs to the surrounding index can be enhanced with decreasing the diameter of FBGs by etching the fiber with HF solution. The sensitivity can be appreciably enhanced by etching the fiber diameters as small as 5.0 μm. A maximum sensitivity of 911.8 nm/riu is achieved. Since a shift of 0.01 nm can be detected, this leads to a detectable change of 1.1×10^-5 in the surrounding index.

Multi-mode Airborne Digital Camera System (MADC) was developed by Institute of Remote Sensing Applications and Shanghai Institute of Technical Physics in 2006. The system is enhancing and optimizing further now. It could realize three modes of wide field, multispectral, and stereophotography based on three 4K*4K CCD digital cameras in the course of taking aerial photography. Several finished aerial experiments have already demonstrated that the system has good performance for aerial photography; both the software and the hardware of MADC could work stably and reliably. Multispectral mode is a popular imaging way in airborne remote sensing. It can obtain multi-bands remote sensing images by using several digital cameras synchronously. The multispectral images can make use for various remote sensing applications, such as environment monitoring, resource researching, military use, and so on. In some special conditions, images which get by using less than 10nm bandwidth narrowband filters can be treat as hyperspectral images; so that we can consider the multispectral imaging way is a new approach for hyperspectral bands selection and data acquisition. In this paper, we will mainly discuss the following questions for the multispectral mode of MADC: the design principle, the basic arithmetic or model, the installation mode, the corresponding aerial experiments, the application fields and the ways of multitspectral images processing. At the same time, some important accessorial devices of MADC are also introduced. The point and conclusion will be received based on the practice installation, operation, ground and aerial experiments.

One of the key issues in establishing an optical fiber sensing system based on fiber Bragg gratings (FBGs) is the selection of a suitable wavelength shift detection scheme in terms of the performance it offers. By use of a compact Fabry-Perot (F-P) tunable filter, the Bragg wavelength variation can be detected with a relatively high speed and satisfying resolution. In this paper, a dynamic strain sensing system based on F-P tunable filter is described, and the F-P tunable filter is demonstrated to have a significant impact on the system. The relationship between the collected spectrum of grating and the 3-dB bandwidth of the F-P tunable filter is discussed. The optimum 3-dB bandwidth of the F-P tunable filter for most FBGs is obtained. It is exhibited in this paper that the demodulation precision and sensitivity of the strain sensing system is influenced by the nonlinearity between the transmission wavelength of the F-P tunable filter and the drive voltage. The drive voltage is rectified using interpolation algorithm. The experimental results illustrate that the average error and the maximum error of the transmission wavelength are decreased by 96.4% and 80.9% respectively. The strain sensitivity of the optimized system is below 3με. The error between the practical strain value demodulated by the system and theoretical value is below 5%.

Based on the Arrayed Waveguide Grating (AWG) equation and output light intensity equation, dual peaks electro-optical AWG is presented, whose properties are analyzed in details in the paper. The experiments for the electro-optical dual peaks AWG are simulated by Optiwave software, and the experimental results verify the theory very well.

The sensor array is structured by the ring optical fiber Sagnac interferometers by way of point sensors to detect and locate the analog source of the acoustic emission (AE). The principle of the ring optical fiber Sagnac interferometer is used to detect ultrasonic waves and locate the AE source is given. One method based on microcomputer intelligent detection is proposed. A steel plate is used as the medium of the acoustic wave propagation, and four sensors are respectively placed on the steel plate to structure a sensor array with point sensors. The home-made analog source of the acoustic emission is applied to do the experiment. When the ultrasonic signal is generated by driving the analog source of the acoustic emission at any position of the steel plate, the ultrasonic signal will be received by the four sensors at the different time. The microcomputer will count the position of the AE source with the time differences of the four received signals and set value of the velocity at which the ultrasonic waves propagating in a solid plate, and then the coordinates of the AE source are displayed by LED.

This paper aims at proposing a modified algorithm based on spectrum adjusting. The theoretical analysis of the error between the real light source spectrum and the Gaussian spectrum is presented. The hardware of the demodulation system is introduced, including the coupler, collimation lens, volume phase grating, focus lens, CCD array, A/D card, and PC. The modified algorithm will adjust the interferometric spectrum of the sensor by getting rid of the effect of the light source spectrum. Experiment was carried out to test the performance of the demodulation system. It can be found from the result that the algorithm has improved the accuracy of the demodulation system significantly. The demodulation accuracy for the strain sensor is better than 0.5 microstrain.

A fiber Bragg grating (FBG) sensors network in the roadbed temperature monitoring system in Qinghai-Tibet railway is presented. This sensor network is composed of FBG sensor chains embedded in the roadbed, slave optical cables, work stations which include the FBG sensor interrogator and the optical router, master optical cables, and center workstation. We give the primary experimental results of this sensor network in monitoring the roadbed temperature of the railway at DK0985+000 near Chumar River. The temperature data was collected after a month when the temperature field in the monitoring hole became stable. This experiment had been carried out for more than one year. The FBG sensor network has successfully measured the temperature in the roadbed with an accuracy of 0.1 centigrade. Furthermore, the experimental result shows the stability and reliability of the FBG sensor network in the harsh environment of Qinghai-Tibet plateau. The prospect of the FBG sensor network in monitoring other parameters in the Qinghai-Tibet plateau is also presented.

The research of fiber optic extrinsic Fabry-Perot interferometer (EFPI) sensors and their applications in concrete structural health monitoring are presented in this paper. Different types of fiber optic EFPI sensors are designed and fabricated. Experiments are carried out to test the performance of the sensors. The results show that the sensors have good linearity and stability. The applications of the fiber optic EFPI sensors in concrete structural health monitoring are also introduced. Ten fiber optic sensors are embedded into one section of the Liaohe Bridge in Qinghuangdao-Shenyang Railway. Field test demonstrates that the results of fiber optic sensors agree well with conventional strain gauges.

The basic principle and the characteristics of a new kind of linear phase retrieval (LPR) wave-front measuring method were analyzed. It is proved that the unknown phase can be retrieved uniquely from only one far-field image with calibration in advance. The principle construction of wave-front sensor developed from the LPR algorithm was described. The performance of the LPR method was tested by numerical simulation on measuring the arbitrary disturbed wave-front. The results showed that the LPR method was feasible on a certain system aberration condition, and it had good ability on high-spacial resolution. In the lab, an experiment setup based on the LPR method had been built. The experiment results testified the feasibility of this method and it could realize highly precision measure by using less amount of detect elements.

Based on Jones matrices theory, the error source and action mechanism of polarized interferometer using four-channel orthogonal signals in nanometer level measurement are researched. It opens a door for selecting optical components, adjusting light set-up and compensating error.The mechanism of nonlinear errors and the variance law of nonlinear errors in laser interferometer, which is caused by nonideal factors of 1/4 wave plates or 1/2 wave plate or all of them, based on polarized phase-shift technology. In this paper, every single error on the polarized interferometer is discussed with the isolation of each wave plate, so that the character of nonlinear error will be reached with composite error. In the experiments, difference delay angle error of two 1/4 wave plates and location angle error is -5°∼5°in interferometer. The aim of this paper is to realize the mechanism of nonlinear errors and the varying rule of nonlinear errors in laser interferometer. All above provide error remove or compensation for laser interferometer in nanometer level measurement with theoretical foundation and search after application.

The composite cavity fibre laser (CCFL) is demonstrated for its capability in maintaining single longitudinal mode operation, whilst having longer cavity length than typical distributed Bragg reflector or distributed feedback fibre lasers, and hence also higher output power. These two attributes should enable the CCFL to be useful in sensing applications. A long cavity length CCFL can be fabricated simply by writing three spectrally matched Bragg gratings directly into a continuous length of doped fibre. This is analogous to the use of feedback cavities in semiconductor laser designs to maintain single longitudinal mode. Results from in-house fabrications show that long cavity length CCFLs can be fabricated to have single longitudinal mode and narrow linewidth characteristics similar to that of a distributed feedback fibre laser, and also significantly higher output power.

A novel composite cavity fibre laser (CCFL) design is being investigated for its use in sensing applications. A CCFL can be fabricated simply by writing three spectrally matched Bragg gratings directly into a continuous length of doped fibre. When strained evenly, so that the strain experienced by both cavities are the same, the strain response of the CCFL is expected to be similar to that of a FBG or single cavity fibre laser sensor. However, if the internal cavities are strained unevenly, simulations derived from theoretical analysis suggest that the wavelength-encoded and intensity-encoded sensitivities can become significantly different from that of a typical single cavity fibre laser. A 3cm/9cm CCFL was tested using three different straining formats, and results agree well with theoretical expectations.

This paper presented signal demodulation scheme of the laser vibration interferometer system using for measurement of low-frequency vibration. Based on principle of phase generated carrier (PGC) modulation and virtual instrument technology, laser vibration signal demodulation on software and hardware platform were established. Taking the PCI6221 multi-function data acquisition device as the core of hardware circuit, real time data acquisition of reference waveform generation and the signal for measurement was realized. Digital PGC algorithm was established by using LabVIEW software workbench, and then vibration signal real time demodulation was realized. The experiment results indicate that the PGC signal demodulation scheme based on virtual instrument technology reduced drift and noise by traditional analog PGC hardware circuit such as analog multiplier and differentiator, enhanced accuracy of signal demodulation, improved system Signal-to-Noise. High accuracy measurement of the low-frequency vibration signals ranging from 10~200Hz comes true, the measuring resolution is better than 0.5nm, and the dynamic range is 110dB.

A novel direct detection method for simultaneous distributed measurement of the temperature and strain along a single mode fiber based on the optical time-domain reflectometer technique is proposed. The Raman backscattering is sensitive to temperature but not to strain, thus the temperature distribution along the fiber can be determined. A twin-channel Fabry-Perot interferometer is designed; of which, the Brillouin channel is used to analyze the strain information within measurement range of 2000 με strain and 400 °C temperature. The frequency center, spectrum bandwidth and intensity changes of Brillouin backscattering are transformed into transmission changes after passing through the Fabry-Perot interferometer. With the look-up table of response functions of detected temperature, the strain profile along the fiber can be known. The Rayleigh channel is design to preset and measure the outgoing laser frequency relative to the Brillouin channel. By modulating the voltage added to the piezoelectric tube of the Fabry-Perot interferometer, the frequency offset of outgoing laser to the Brillouin channel can be preset; the temperature dynamic range can be extended.

The stability of the mean wavelength of Er-droped superfluorescent fiber sources with a direct sampling control unit, intended for fiber-optic gyroscope applications, are explored theoretically and experimentally. The mean wavelength variation versus ambient temperature is measured, and the experimental result shows that the mean wavelength is correlated to the sampling voltage, which is in good agreement with theoretical analysis. The thermal effects are modeled to reduce the influence of temperature variation based on the characteristic of monitoring photodiode, and the control algorithms based on the temperature model are implemented in a standard microprocessor system without additional hardware. The results show that the temperature stability of the SFS mean wavelength is better than 1ppm/°C over the entire range of operating temperature, which confirm that this method is effective, and meet the stringent requirements of the FOG.

In a weigh-in-motion(WIM) scale, the load cells are the paramount parts, and the traditional strain gauges are used as main sensing elements. However, the performance of these electrical sensors is poor in durability and stability. Fibre Bragg grating (FGB) is of good sensing characters, this experiment therefore used them to replace the strain gauges in the load cells, and to apply in a real WIM system. Two FBGs were adhered on a cantilever load cell by means of a special fiber holder, one of them acted as a tensive sensor, the other acted as a compressive sensor. To subtract their measuring results, the response was doubled, furthermore, the environmental interference was eliminated. The repeatability was calibrated reaching 0.02% in full 0-20 ton scale. Four FBG load cells were set as supports of weighting plate in an axial WIM scale to weigh vehicles. The results showed that the FBG scale performed better than strain gauge scale under the same WIM dynamic processing program. Under the speed of 11km/h, the measuring accuracy can be kept within 1%, while the measuring accuracy of strain gauge scale was about 3%.

Optical Kerr effect in the passive ring-resonator optical fiber gyroscope (PORG) made from hollow-core photonic band-gap (PBG) fiber is analyzed theoretically using a simple optical field overlap method, comparing it with the passive ring-resonator optical fiber gyroscope made from conventional single mode fiber (SMF). The theoretical evidence show that optical Kerr effect induced rotation rate shift in PORG made from hollow-core PBG fiber should be reduced by 1~2 orders at different ring resonator length when the optical source spectral width is fixed.

We demonstrate a laser Doppler velocimeter (LDV) based on self-mixing effect in a single longitudinal mode VCSEL for velocity measurement of flowing milk using Polymer Optical Fiber (POF). We find that self-mixing signal in frequency domain was broadened using POF compare with space coupled. The flow velocity was measured when POF outside and inside the milk. Their self-mixing signals of power spectrum can be fitted with Gaussian and exponential decay function, respectively. The differences of self-mixing signal in frequency domain when POF outside and inside milk are discussed. Due to POF have the advantages of flexibility and compatible with biology, this velocimeter can also be used for the measurement of blood flow in vivo.

The paper deals with the spacecraft attitude determination problem using a new kind of star tracker with large FOV based on CMOS APS. Star tracker has been developed since 1970s and proved to be the most accurate sensor ever used in the spacecraft attitude determination systems. But the traditional CCD star tracker also has some disadvantages, such as small FOV, high power consumption, low sample rate and low working angular rate limit which prevent the use of CCD star tracker in attitude large angle maneuvering process. The new kind of star tracker based on CMOS APS has no such disadvantages and is more applicable on modern low-cost agile small satellites. Its higher sample rate and working angular rate limit over traditional CCD star tracker make it more adapt for spacecraft angular velocity determination. Because of the large FOV of the star tracker, the mathematical model of traditional CCD star tracker with a small FOV is not appropriate. So a new mathematical model was quoted to fit the star tracker with a large FOV. An alternative adaptive algorithm was also introduced in the paper. It can help the EKF algorithm work lacking of accurate covariance of the observation noise. An optimal estimation algorithm was used to estimate the angular velocity directly from the star tracker measurements. Mathematic simulation results indicate the CMOS APS star tracker can give accurate attitude information and estimated angular rate. The method can be used as the chief attitude determination system design of low-cost satellite without gyros, or be used as a backup strategy in the event of gyro failures to enhance the reliability of the attitude determination system.

In this paper, a novel biosensor technique for identification of high temperature resistant species based on quantitative measurement of delayed fluorescence (DF) is described. The biosensor, which uses light-emitting diode lattice as excitation light source, is portable and can detect DF emission from plants in vivo. Compared with its primary version in our previous report, the biosensor presented here can better control environmental factors. Moreover, the improved biosensor can automatically complete the measurements of light response curves of DF intensity in a programmed mode. The testing of the improved biosensor has been made in two maize species (Zea May L.) after high temperature treatment. Contrast evaluations of the effects of heat stress on seedlings photosynthesis were made from measurements of net photosynthesis rate (Pn) based on consumption of CO₂. Current testing has demonstrated that the DF intensity well correlates with Pn in each plant species after heat stress. We thus conclude that the DF technique is a breakthrough to traditional strategy of identifying the differences in heat tolerance based on gas exchange, and can provide a reliable approach for rapid and non-invasive determination of the effects of heat stress on photosynthesis and identification of high temperature resistant species.

The structure and function of chloroplast in plant can be affected by herbicide, resulting in the decrease in photosynthetic capacity. The photosystem II (PSII) in plants is considered to be the primary site where light-induced delayed fluorescence (DF) is produced. In this study, a simple analytical model of DF has been developed to diagnose the damages of photosynthesis caused by herbicides based on the charge recombination theory. Using a home-made portable DF detection system, we have studied the effects of two different kinds of herbicides on decay kinetics of DF in soybean (Glycine max (L.), Jinghuang No. 3). Current investigations have demonstrated that the analytic equation of DF decay dynamics we proposed here can accurately determine the extent of damage of herbicides to photosynthetic metabolism and truly reflect the mechanism and site about which herbicides inhibit photosynthetic electron transport chain. Therefore, the decay kinetics of DF with proper calibration may provide a promisingly new and practical means for pharmacological analysis of herbicides and damage-diagnosis of photosynthetic metabolism. The DF technique could be potentially useful for detecting the effects of herbicide on plant performance in vivo and screening new generation of promising herbicides with low toxicity and superhigh efficiency.

Lidar is an important equipment for the accurate detection of underwater targets. In lidar measurements of underwater target, the energy and width of the laser pulse will affect the results when using PMT as receiver, which has been proved by data processing and analysyses. To avoid the effect and enhance the accuragy of underwater, many methods such as controling the energy of the laser pulse, reducing the pulse width are taken. The experiment results of underwater target measurement are discussed.

The paper reports a demonstration of a reflective Er-Doped-Fiber-Amplifier (EDFA) system. The system is designed for optical pre-amplification in remote fiber optic hydrophone system. In the reflective EDFA, a Fiber-Bragg-Grating (FBG) is placed at the EDFA output end to reflect the signal and to prevent the ASE feedback. A fiber with a reflecting end is also placed at the output end to reflect the pump. An experiment is also demonstrated to test the gain (G), noise figure (NF, intensity noise and phase noise of the reflective EDFA in comparison with standard, single-pass configuration EDFA. The proposed EDFA shows higher gain but lower noise figure and lower relative intensity noise and phase noise than conventional standard configuration. While its gain is nearly twice that of the standard configuration, its NF is about 4dB lower than that of a standard configuration. In addition, the reflective EDFA reduces the phase noise at 1KHz and the relative intensity noise of the hydrophone system when it is high bumped.

We report our recent work on photonic sensors and devices based on air-silica photonic crystal fibers (PCFs), including splicing PCFs to single mode fibers, two-mode index-guiding PCFs and their applications in sensors and wavelength tuning devices, long period gratings written on index-guiding and photonic bandgap (PBG) PCFs, and low-contrast PBG PCFs made by filling the holes of air-silica hollow-core PBG PCFs with liquid of index lower than silica, and gas detection with index-guiding and PBG PCFs.