Second-order sensitivity effects on optical fiber polarimetric temperature sensor and strain sensor

We analyze the second-order sensitivity effects of a polarimetric temperature sensor and a strain sensor. Such effects are shown to be important for a larger temperature change or strain and are demonstrated by the analysis of the errors between the experimentally measured data and the curves of linear and second-order polynomial regressions, respectively. It is also shown that for a small temperature change or strain, higher accurate values of the two parameters can be obtained only from linear regression. The cross-sensitivity effect is also studied experimentally.     

Temperature-insensitive fiber Bragg grating tilt sensor

A temperature-insensitive optical fiber tilt sensor is presented. The sensor scheme uses a prestrained fiber Bragg grating to sense the strain, which depends on the tilt angle. To compensate for the temperature effect, materials that have different linear thermal expansion behaviors are used for implementation of the sensor body. The differentiation in the linear thermal expansion would then cause a counter effect to the original temperature effect. Experimental tests show an accuracy of +/-0.167 degrees in tilt angle measurement. A temperature stability better than +/-0.33 degrees over the temperature range from 27 degrees C to 75 degrees C is demonstrated. The resolution 0.0067 degrees in tilt angle measurement is achieved by using our preliminary sensor with a dimension of 1 6 x 5 x 5 cm(3).     

Development of a polarimetric optical fiber sensor for electronicmeasurement of high pressure

The theoretical understanding of the principle of pressure-induced polarization coupling is discussed, and the improved construction, operation, and temperature desensitization of a high-pressure (up to 100 MPa) fiber-optic sensor in two configurations is described. The sensor exploits the effect of polarization coupling between two orthogonally polarized eigenmodes of a highly birefringent, polarization-preserving optical fiber which serves as the sensing element. An idea of temperature desensitization of the sensor output signal is demonstrated. The requirements for an electronic measurement system based on the sensor are discussed, including indentification of the parametric and functional specifications and constraints of such a system     

Tunable multiwavelength fiber laser based on a double Sagnac HiBi fiber loop

A tunable multiwavelength fiber laser based on double Sagnac loops is proposed and demonstrated. Comb filter characteristics of single and double Sagnac loops are analyzed by Jones matrix. Simulated results show that there are better tunability and controllability with double loops than with a single loop, and this also has been confirmed by experimental results. By adjusting the polarization controller and the length of the polarization maintaining fiber the wavelength range, wavelength spacing, and laser linewidth can be tuned. Experimental results indicate that the linewidth of the multiwavelength fiber laser was 0.0187 nm and the optical sidemode suppression ratio was 50 dB.     

一种用于低频测量的光纤光栅振动传感器

利用光纤光栅敏感技术,设计了一种用于低频测量的光纤光栅振动传感器.该传感器采用了等强度悬臂梁作为振动传感元件,并在等强度悬臂梁的上下双面优化布置性能匹配的两个光纤光栅,一个为振动敏感测量光栅,另一个为信号匹配滤波解调光栅.该结构设计可以补偿温度的不利影响,同时也提高了传感器信号检测的灵敏度.实测结果表明,该传感器可以用于25 Hz以下的低频目标的振动测量.     

Chemical gas sensor application of open-pore mesoporous thin films based on integrated optical polarimetric interferometry

Chemical gas sensors that employ integrated optical polarimetric interferometry were fabricated by the sol-gel synthesis of transparent mesoporous thin films of TiO2-P2O5 nanocomposite on tapered layers of TiO2 sputtered on tin-diffused glass waveguides. Atomic force microscopy images of the mesoporous thin film clearly show the open pore mouths on the film surface that favor rapid diffusion and adsorption of gas-phase analytes within the entire film. Adsorption of gas and vapor induces changes (Deltan) in the refractive index of the mesoporous thin film that lead to shifts in the phase difference between the fundamental transverse electric and magnetic modes simultaneously excited in the glass waveguide via single-beam incidence. Upon exposure to NH3 gas at concentrations as low as 100 ppb in dry air at room temperature, the sensor exhibits a reversible change in the phase difference with the response and recovery times of less than 60 and 90 s, respectively. It is unexpected that the sensor is unresponsive to either NO2 or C6H6 vapor, leading to a somewhat selective sensitivity to NH3. Determination of Deltan was carried out with a combination of the experimental results and the theoretical calculations. The sensor design represents a novel, effective, and easily accessible approach to mesoporous thin-film-based integrated optical chemical sensors.     

Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm

Use of photonic crystal fibers (PCFs) in the field of sensing is relatively new. We propose the application of a PCF for pressure sensing. The fiber analyzed is a polarization-maintaining PCF that has negligible sensitivity to temperature, making it an ideal candidate for pressure sensing in harsh environments. On the basis of theoretical and experimental analysis, PCF is proposed to be applied as a temperature-compensated pressure sensor. Detailed theoretical analysis and the experiment carried out are described to show the concept of the sensor.     

Side-hole two-core microstructured optical fiber for hydrostatic pressure sensing

A novel side-hole two-core microstructured optical fiber (STMOF) is proposed for hydrostatic pressure sensing. The two solid fiber cores are surrounded by a few small air holes and two large air holes, and are separated by one small air hole in the center of the cross section of the STMOF. The two large air holes that we called side holes essentially provide a built-in transducing mechanism to enhance the pressure-induced index change, which ensures the high sensitivity of the hydrostatic pressure sensor based on the STMOF. Mode coupling between the two fiber cores of the STMOF has been investigated, which provides a pressure-dependent transmission spectrum by injecting a broadband light into one fiber core of the STMOF on one side and detecting output spectrum on another fiber core on the other side. Our simulations show that there is a one-to-one correspondence between the hydrostatic pressure applied on the STMOF and the peak wavelength shift of the transmission spectrum. A hydrostatic pressure sensor based on an 8 cm STMOF has a sensitivity of 0.111 nm/Mpa for the measurement range from 0 Mpa to 200 Mpa. The performances of hydrostatic pressure sensors based on STMOFs with different structure parameters are presented.     

溶胶—凝胶法制备基于荧光猝灭原理的光纤氧传感器在线监测水中溶解氧

利用氧分子对金属钌化合物的荧光具有猝灭作用的特性,构造出基于荧光猝灭原理的光纤氧传感器。就用于水中溶解氧在线监测的光纤光谱仪的搭建、传感器探头的设制及传感膜的制作过程进行探索,并对传感器的响应性能进行考察。结果表明以联吡啶钌等作为荧光指示剂以溶胶-凝胶法制备的传感膜对溶解氧的响应具有良好的可逆性,稳定性,较快的响应时间和较长的使用寿命。与标准法相对照,用本仪器系统测定了不同盐度的人工海水中的溶解氧浓度,两种方法在不同浓度水平下的溶解氧测定值均无显著性差异。本法的日内和日间RSD在1.7％～5.0％之间。     

Micromachined optical fiber current sensor

We describe a micromachined optical fiber current sensor. The sensing element consists of a squared silicon membrane (8 mm long and 20 mum thick) that has a cylindrical permanent magnet (NdFeB alloy, 3-mm diameter, 1.5 mm high) fixed on its central region. This structure allows the permanent magnet to vibrate in the presence of the magnetic field gradient generated by an ac. A linear relation between the electrical current and the magnet displacement was measured with white-light interferometry with an optical fiber low-finesse Fabry-Perot microcavity. A measurement range of 0-70 A and a minimum detectable intensity of 20 mA were obtained when distance D between the membrane and the electrical power line was 5 mm. The output signal directly shows a linear response with distance D.     

Multimicrobial sensor using microstructured three-dimensional electrodes based on silicon technology

Two microbial strains with different substrate spectra were immobilized separately within a single biosensor chip featuring four individually addressable platinum electrodes. These were sputtered onto the inner surface of four isolated pyramidal cavities ("containments") micromachined on a silicon wafer. The biosensor chip was integrated into a flow-through system to measure the oxygen consumption of the immobilized microorganisms in the presence of assimilable analytes. As a model system, a yeast for the determination of biochemical oxygen demand (BOD) and a strain capable of degrading polycyclic aromatic hydrocarbons (PAH) were chosen. It was shown that the simple and mass-producible containment sensor exhibits good performance data: lower detection limit 0.1 mg/L naphthalene and 1 mg/L sensor-BOD; calibration range up to 30 mg/L; precision 3-6%; response time 2-3 min; service life up to 40 days; shelf life at 4 degrees C 6 months. The versatility of the multimicrobial sensor was demonstrated by measuring ordinary municipal wastewater samples as well as various aqueous samples contaminated with PAH. The concept of a multimicrobial sensor not only enlarges the substrate spectrum for sum parameters such as BOD but leads to additional information which allows for a more differentiated and immediate knowledge of sample composition. Using chemometrical data analysis, the multimicrobial sensor lays a foundation for developing an "electronic tongue".     

一种基于相干光时域反射的分布式光纤振动传感系统研制

针对基于相干光时域反射的分布式光纤振动传感系统中数据量庞大,且需要信号发生器外部驱动,集成度低的缺点,利用现场可编程逻辑门阵列实现传感数据的高速采集与声光调制器的同步驱动,采用USB 3.0实现采集模块与上位机的实时数据传输。搭建一种基于相干光时域反射的分布式光纤振动传感系统,利用本地光与后向瑞利散射光的拍频效应,实现对微弱后向瑞利散射光信号的探测,并提高系统的传感距离。采用正交相位解调方法获取振动信号的位置信息。实验结果表明:该系统可在22 km传感光纤上对振动信号进行有效定位,定位误差在20 m以内,且系统对正弦波和方波等不同形态的振动信号定位效果一致。     

Optical router for optical fiber sensor networks based on a liquid crystal cell

Optical fiber sensor networks are evolving rapidly. They are used because of the inert nature of optical fibers allowing no electromagnetic interference and safe applications in inflammable atmospheres; other relevant characteristics are their low weights and wide bandwidths as a transmission medium. In any case, it is very interesting to have specific components such as optical routers for selecting a certain path in a network with no optical to electrical and electrical to optical conversions. In this paper, we propose an all-optical router based on liquid crystals, polarizers, and a spatial split polarization beam splitter. The implemented device is designed to operate with visible light and it has been tested with plastic optical fibers. It has a crosstalk of 14 dB between selected ON channels and nonoperative OFF channels and 11-dB insertion losses. An average switch time of 100 ms is measured. The device checks the optical power level in each channel and, in case of failure, automatically switches to an operative channel while an alarm is activated.     

An optical fiber chemical sensor for mercury ions based on a porphyrin dimer

The synthesis of a novel fluoroionophore, 5-p-[[4-(10',15',20'-triphenyl-5'-porphinato) phenyloxyl]-1-butyloxyl]phenyl-10,15,20-triphenylporphine (DTPP), and its application for preparation of a Hg(II)-sensitive optical fiber chemical sensor are described. The response of the sensor is based on the fluorescence quenching of DTPP by coordination with Hg(II). The porphyrin dimer-based sensor shows a linear response toward Hg(II) in the concentration range 5.2 x 10(-7)-3.1 x 10(-4) mol x L(-1), with a working pH range from 2.4 to 8.0. The sensor shows excellent selectivity for Hg(II) over transition metal cations including Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II), and Fe(III). As a sensing agent, the porphyrin dimer shows obviously better fluorescence response characteristics toward Hg(II) compared to porphyrin monomer or metalloporphyrin. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for determination of Hg(II) in water samples.     

A dual modality optical fiber sensor

We propose and demonstrate a fibre optic system based on bi-tapered silica fibre that can simultaneously measure strain and fibre curvature. Both modalities on the signal can be extracted with no measurable crosstalk between them. The experimental signal has a pure phase modulation when strain is applied to the tapered fibre optic section of the sensor and the signal shows only intensity modulation when an un-tapered fibre section is bent. High sensitivity is achieved from the experimental results for strain and bending losses and the estimation of measurement errors is 0.2 and 0.1%, respectively. This system offers low-cost, compactness and it can be adapted for structural health monitoring.     

A reflectometric optical fiber temperature sensor

A reflectometric fiber-optic temperature sensor was manufactured and characterized. The sensing probe is obtained by replacing the cladding with a temperature sensitive liquid on a short length of fiber. Its reduced dimensions make it suitable for monitoring applications whenever a high spatial resolution is required. A numerical modeling of the sensor, based on a ray-tracing technique, was carried out. The metrological performance of the first prototype seems to be very interesting in terms of accuracy and, above all, response time. A system for multipoint temperature measurements is also described.     

Sensitive acoustic vibration sensor using single-mode fiber tapers

Optical fiber sensors are a good alternative to piezoelectric devices in electromagnetic sensitive environments. In this study, we reported a fiber acoustic sensor based on single-mode fiber (SMF) tapers. The fiber taper is used as the sensing arm in a Mach-Zehnder interferometer. Benefiting from their micrometer dimensions, fiber tapers have shown higher sensitivities to the acoustic vibrations than SMFs. Under the same conditions, the thinnest fiber taper in this report, with a diameter of 1.7 μm, shows a 20 dB improvement in the signal to noise ratio as compared to that of an SMF. This acoustic vibration sensor can detect the acoustic waves over the frequencies of 30 Hz-40 kHz, which is limited by the acoustic wave generator in experiments. We also discussed the phase changes of fiber tapers with different diameters under acoustic vibrations.     

光纤矢量水听器指向性锐化技术研究

1引言光纤水听器和矢量水听器是近些年来出现的新型水听器,与普通声压水听器相比,它们有着较为优越的性能[1],光纤矢量水听器则结合了二者的优势,有着更为广阔的应用前景,在本文中,我们分析了光纤矢量水听器的指向性并对其进行了海试实验验证。     

Extrinsic Fabry-Perot cavity optical fiber liquid-level sensor

An optical fiber liquid-level sensor based on an extrinsic Fabry-Perot (FP) cavity is proposed and demonstrated. The FP cavity consists of the end of the single-mode optical fiber and the elastic silicon layer. Liquid pressures act on the mechanical construction to change the cavity length, resulting in differential phase shifts that may be observed as variations of the output signal intensity. Self-compensated steps have been taken to obtain high accuracy and long-term stability in realistic circumstances. Experimental results indicate that accuracy of 2 mm over a full scale of 3.5 m (water) is obtained under ambient temperature 10-38 degrees C. The sensor can be used to measure liquid levels continuously and accurately in explosive and flammable environments.     

A novel temperature sensor and variable optical attenuator based on a high-birefringence fiber loop mirror

A novel variable optical attenuator based on a high-birefringence fiber loop mirror is described. The fiber loop mirror is placed in a controlled-temperature chamber. As the temperature is increased, the transmission spectrum exhibits a shift, while virtually not changing its shape. The degree of attenuation at a wavelength of 1558 nm exceeds 30 dB, while the introduced losses are about 2.5 dB. The temperature-induced shift of the spectrum is strictly linear. The response of the temperature sensor based on this effect is linear with a correlation coefficient of 0.9997. The obtained experimental data are interpreted based on the results of numerical modeling.