An all optical fiber gas sensor of NH3 and CO based on based on the spectral absorption and harmonic detection

An all optical fiber gas sensor is presented to detect the concentration of NH3 and CO. Based on the spectral absorption, The wideband light source is used to reflect two narrowband spectra by fiber grating of different duty. and piezoelectric ceramics to obtain narrowband output light. The high sensitivity detection can be measured from the second harmonic signal. The two narrowband spectra are corresponding to the absorption spectra of NH3 and CO. Concentration detection are realized by the detection of variety of light intensity. Sensitivity is proved and cost is reduced.

Distributed optical fiber acoustic sensor for in situ monitoring of marine natural gas hydrates production for the first time in the Shenhu Area,China

The distributed acoustic sensor(DAS)uses a single optical cable as the sensing unit,which can capture the acoustic and vibration signals along the optical cable in real-time.So it is suitable for monitoring downhole production activities in the process of oil and gas development.The authors applied the DAS system in a gas production well in the South China Sea for in situ monitoring of the whole wellbore for the first time and obtained the distributed acoustic signals along the whole wellbore.These signals can clearly distinguish the vertical section,curve section,and horizontal production section.The collected acoustic signal with the frequency of approximately 50 Hz caused by the electric submersible pump exhibit a signal-to-noise ratio higher than 27 dB.By analyzing the acoustic signals in the production section,it can be located the layers with high gas production rates.Once an accurate physical model is built in the future,the gas production profile will be obtained.In addition,the DAS system can track the trajectory of downhole tools in the wellbore to guide the operation.Through the velocity analysis of the typical signals,the type of fluids in the wellbore can be distinguished.The successful application of the system provides a promising whole wellbore acoustic monitoring tool for the production of marine gas hydrate,with a good application prospect.

NOVEL SPECTRUM ABSORPTION OPTICAL FIBER METHANE SENSOR

Based on spectrum principle and analyzing the infrared absorption spectrum ofmethane, a kind of optical fiber methane gas sensor and its system are developed. DFBLD(Distributedfeedback laser diode) in 1 300 nm waveband is used as illuminant and phase-detecting technology isused to carry out harmonic wave detecting the concentration of methane. The sensitivity can arriveat 10^(-5). Experiments results show that the performance targets of the sensor such as sensitivitycan basically satisfy the requests of methane detection.

DISTRIBUTED OPTICAL FIBER SENSOR FOR LONG-DISTANCE OIL PIPELINE HEALTH

A fully distributed optical fiber sensor （DOFS） for monitoring long-distance oil pipeline health is proposed based on optical time domain reflectometry （OTDR）. A smart and sensitive optical fiber cable is installed along the pipeline acting as a sensor, The experiments show that the cable swells when exposed to oil and induced additional bending losses inside the fiber, and the optical attenuation of the fiber coated by a thin skin with periodical hardness is sensitive to deformation and vibration caused by oil leakage, tampering, or mechanical impact. The region where the additional attenuation occurred is detected and located by DOFS based on OTDR, the types of pipeline accidents are identified according to the characteristics of transmitted optical power received by an optical power meter, Another prototype of DOFS based on a forward traveling frequency-modulated continuous-wave （FMCW） is also proposed to monitor pipeline. The advantages and disadvantages of DOFSs based on OTDR and FMCW are discussed. The experiments show that DOFSs are capable of detecting and locating distant oil pipeline leakages and damages in real time with an estimated precision of ten meters over tens of kilometers.

Optically Powered Pressure Sensor with Optical Fiber Link

An optically powered sensor for measuring pressure which is linked by optical fiber is developed in new scheme. Its pulse position modulation (PPM) optical signal and optical supply power for electronics in probe are transmitted via a single optical fiber. The optical power is carried by a 1 300 nm laser diode (LD) and the sensing data are carried by a 850 nm LED. The remote probe uses all CMOS chips and particular modulations (PPM and PWM). Its electrical consumption including signal manipulation and LED driven current from optically converted is less than 100 μW. The laser diode supplies 5 mW optical power into the fiber. A photodetector converts sufficiently this power into electrical power to drive the whole probe operation. The optically powered distance gets up to 500 m. The novel sensor combines optical fiber and electronics technology into a system. Because of using the principle of ratio measurement between measured and reference signals, as well as light feedback,the system is available with high reliable, outstanding accuracy and repeatability.

PLASMA RESONANCE FIBER OPTIC SENSOR FOR CURE MONITORING OF EPOXY COMPOSITE

The plasma resonance fiber optic sensor has a research values in theory and is widely used in engineering because of its simple structure and high sensitivity. It is a simple and sensitive method to measure the refractive index with optical fiber plasma wave. We make use of this characteristic to manufacture the plasma resonance fiber optic sensor which can detect the cure of epoxy compo site. We study the method of testing the solutions which have different refractive index with plasma resonance fiber optic sensor. A fiber optic sensing probe which has reliable performance and convenient operation for detecting the refractive index has been designed. The system for detecting the solution refractive index is developed and used to measure the refractive index of epoxy during the different phases in the cure process. Result shows that this system is credible and stable, the parameters tested are in accord with the facts.

Remote structural health monitoring with serially multiplexed fiber optic acoustic emission sensors

Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points along the length of a single fiber.Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of' crack locations,Labora- tory experiments on plain concrete beams and post-tensioned FRP tendons were pcrlormed to evaluate the crack detection capability of the sensor system.The acoustic emission sensor was able to detect initiation,growth and location of the cracks in concrete as well as in the FRP tendons.The AE system is potentially suitable lot applications involving health monitoring of structures following an earthquake.

Realization of Rapid Debugging for Detection Circuit of Optical Fiber Gas Sensor： Using an Analog Signal Source

An optical fiber gas sensor mainly consists of two parts： optical part and detection circuit. In the debugging for the detection circuit, the optical part usually serves as a signal source. However, in the debugging condition, the optical part can be easily influenced by many factors, such as the fluctuation of ambient temperature or driving current resulting in instability of the wavelength and intensity for the laser; for dual-beam sensor, the different bends and stresses of^the optical fiber will lead to the fluctuation of the intensity and phase; the intensity noise from the collimator, coupler, and other optical devices in the system will also result in the impurity of the optical part based signal source. In order to dramatically improve the debugging efficiency of the detection circuit and shorten the period of research and development, this paper describes an analog signal source, consisting of a single chip microcomputer （SCM）, an amplifier circuit, and a voltage-to-current conversion circuit. It can be used to realize the rapid debugging detection circuit of the optical fiber gas sensor instead of optical part based signal source. This analog signal source performs well with many other advantages, such as the simple operation, small size, and light weight.

Advances in Optical Fiber Bragg Grating Sensor Technologies

The authors review their recent advances in the development of optical fiber Bragg grating （FBG） sensor technologies. After a brief review of the fiber grating sensors, several newly developed FBG sensors are described. With the continuous development of fiber materials, microstructures and post-processing technologies, FBG sensors are still creative after the first demonstration of permanent gratings thirty years ago.

On-Line Defect Detection of Aluminum Coating Using Fiber Optic Sensor

Aluminum metallization using the sprayed coating for exhaust mild steel （MS） pipes of tractors is a standard practice for avoiding rusting. Patches of thin metal coats are prone to rusting and are thus considered as defects in the surface coating. This paper reports a novel configuration of the fiber optic sensor for on-line checking the aluminum metaUization uniformity and hence for defect detection. An optimally chosen high bright 440 nm BLUE LED （light-emitting diode） launches light into a transmitting fiber inclined at the angle of 60° to the surface under inspection placed adequately. The reflected light is transported by a receiving fiber to a blue enhanced photo detector. The metallization thickness on the coated surface results in visually observable variation in the gray shades. The coated pipe is spirally inspected by a combination of linear and rotary motions. The sensor output is the signal conditioned and monitored with RISHUBH DAS. Experimental results show the good repeatability in the defect detection and coating non-uniformity measurement.

Optical fiber hydrogen sensor using metasurfaces composed of palladium

Palladium-based hydrogen sensors have been typically studied due to the dielectric function that changes with the hydrogen concentration. However, the development of a reliable, integral, and widely applicable hydrogen sensor requires a simple readout mechanism and an optimization of the fast detection of hydrogen. In this work, optical fiber hydrogen sensing platforms are developed using an optimized metasurface, which consists of a layer of palladium nanoantennas array suspended above a gold mirror layer. Since the optical properties of these palladium nanoantennas differ from the traditional palladium films, a high reflectance difference can be achieved when the sensor based on the metasurface is exposed to the hydrogen atmosphere. Finally, the optimized reflectance difference ΔR of ~0.28 can be obtained when the sensor is exposed in the presence of hydrogen. It is demonstrated that this integrated system architecture with an optimized palladium-based metasurface and a simple optical fiber readout system provides a compact and light platform for hydrogen detection in various working environments.

Detection of Amines in Lamb Spoilage by Optical Waveguide Sensor Based on Bromophenol Blue-Silicon Composite Film

We herein report the development of a bromophenol blue(BPB)-silicone composite film/K^+-exchange glass optical waveguide(OWG)sensor for the detection of amines produced during the spoilage of lamb.the optical and structural properties of the sensitive thin film were studied by ultra violet-visible(UV-Vis)spectroscopy,and the light source of the OWG detecting system was selected.Gas sensing measurements showed that the sensor exhibited a good selectivity,higli sensitivity,and short response-recovery time towards volatile amine gases in the 0.00117一11.72 mg/g range.The as-prepared optical waveguide device was subsequently applied in the determination of gases(namely trimethylamine,dimethylamine,and ammonia)emitted from the lamb samples(5g)stored at room temperature(25℃)and in a refrigerator(5℃)for 0—4 d,and the total volatile basic nitrogen(TVB-N)contents were detected by UV-Vis spectroscopy,and the results were compared witli those obtained using our detector.It was found that the sensing element was capable of detecting mixed gases produced by the decomposition of lamb samples in a refrigerator for 0.5 h,where the TVB-N content was lower than 35μg/g.

Spectral Absorption Gas Sensor Based on Anti-Resonant Reflecting Optical Waveguide

An air-silica microstructure optical fiber based on the anti-resonant reflecting optical waveguide （ARROW） principle was used to develop a spectral absorption gas sensor. The ARROW fiber has an air core and an air cladding layer. An ARROW fiber with a length of 725mm was used to construct a sensing system to detect acetylene gas. The gas was injected into the fiber from one end of the fiber. The transmission spectra were collected using an optical spectrum analyzer. The results indicate that the system can detect the gas of different concentrations and has the good system linearity. The response time of the system is about 200 s.

基于Sagnac干涉计谐波游标效应的光纤温度传感器

提出一种基于双萨格奈克(Sagnac)干涉计谐波游标效应的光纤温度传感器,在该传感器中,传感干涉计中熊猫光纤的长度约为参考干涉计中熊猫光纤的整数倍。理论分析与实验结果表明,当游标放大倍率相同时,基于谐波游标效应和基于普通光学游标效应的双Sagnac干涉计具有相同的温度灵敏度,但谐波游标效应对应的熊猫光纤长度失谐量明显大于普通光学游标效应,且阶数越高对应的失谐量越大。由于失谐量越大,游标放大倍率越容易控制和实现,因此,从制备角度上讲,谐波游标效应明显优于普通光学游标效应。该研究可为后续光学游标效应的研究提供重要参考。

微分散液滴的光纤检测研究

微分散是微化工技术的重要组成部分,传统利用显微摄像分析和统计微分散液滴的方法成本高,不易推广。提出了一种基于光纤传感的微分散液滴在线检测技术,该方法基于漫反射光纤、光纤传感器、数据采集卡和LabVIEW程序实现了微通道内液滴生成频率和长度的在线检测,满足0.21 mm以上直径液滴的检测,检测频率上限为500 Hz,当液滴通过光纤时间超过15 ms时,还可检测液滴长度。研究结果表明光纤直径和光纤传感器响应时间是影响该方法检测性能的主要因素,与相似平台对比,以较低的成本实现了较高检测性能。

一种新型二氧化硅多孔材料固定化酶光纤葡萄糖传感器的研究

目的 研制一种新型的基于氧敏感指示剂Ru(bpy)3Cl2和固定化葡萄糖氧化酶(GOD)的复合敏感膜光纤传感器,用于实时检测葡萄糖溶液质量浓度。方法 以多孔SiO_(2)纳米粒子为载体固定GOD,并采用溶胶-凝胶法同时加入Ru(bpy)_(3)Cl_(2)制备葡萄糖敏感膜,通过提拉法在光纤端面沉积敏感膜制成光纤传感探头,搭建光纤传感器用于实时检测葡萄糖溶液质量浓度。结果 光纤传感器检测葡萄糖溶液质量浓度为50~900mg/dL(2.78~50.00mmol/L),在用于实时监测葡萄糖溶液质量浓度变化时响应时间短,测试标准曲线线性良好。结论 SiO_(2)多孔材料固定化酶光纤葡萄糖传感器具有灵敏度高、响应速度快、检测范围大等优点,未来可以检测人体血液中的葡萄糖质量浓度。

Real-Time Distributed Fiber Optic Sensor for Security Systems： Performance, Event Classification and Nuisance Mitigation

The success of any perimeter intrusion detection system depends on three important performance parameters： the probability of detection （POD）, the nuisance alarm rate （NAR）, and the false alarm rate （FAR）. The most fundamental parameter, POD, is normally related to a number of factors such as the event of interest, the sensitivity of the sensor, the installation quality of the system, and the reliability of the sensing equipment. The suppression of nuisance alarms without degrading sensitivity in fiber optic intrusion detection systems is key to maintaining acceptable performance. Signal processing algorithms that maintain the POD and eliminate nuisance alarms are crucial for achieving this. In this paper, a robust event classification system using supervised neural networks together with a level crossings （LCs） based feature extraction algorithm is presented for the detection and recognition of intrusion and non-intrusion events in a fence-based fiber-optic intrusion detection system. A level crossings algorithm is also used with a dynamic threshold to suppress torrential rain-induced nuisance alarms in a fence system. Results show that rain-induced nuisance alarms can be suppressed for rainfall rates in excess of 100mm/hr with the simultaneous detection of intrusion events. The use of a level crossing based detection and novel classification algorithm is also presented for a buried pipeline fiber optic intrusion detection system for the suppression of nuisance events and discrimination of intrusion events. The sensor employed for both types of systems is a distributed bidirectional fiber-optic Mach-Zehnder （MZ） interferometer.

Distributed optical fiber vibration sensing system based on polarization detection

A novel distributed optical fiber vibration sensing system based on polarization detection is proposed and demonstrated. A Faraday rotator mirror is employed at the end of the system, which eliminates the slow polarization variation of signal light and only responses to rapid polarization change caused by external vibration interference. Based on the sensing signal characteristics, the location of polarization disturbance point can be detected accurately. Experiments on polarization controller simulation and actual vibration detection show that a higher localization accuracy better than 1% is successfully obtained in 13.8 kin, 21.2 km and 35.8 km sensing fibers systems.

Research Progress in the Key Device and Technology for Fiber Optic Sensor Network

The recent research progress in the key device and technology of the fiber optic sensor network （FOSN） is introduced in this paper. An architecture of the sensor optical passive network （SPON）, by employing hybrid wavelength division multiplexing/time division multiplexing （WDM/TDM） techniques similar to the fiber communication passive optical network （PON）, is proposed. The network topology scheme of a hybrid TDM/WDM/FDM （frequency division multiplexing） three-dimension fiber optic sensing system for achieving ultra-large capacity, long distance, and high resolution sensing performance is performed and analyzed. As the most important device of the FOSN, several kinds of light source are developed, including the wideband multi-wavelength fiber laser operating at C band, switchable and tunable 2 μm multi-wavelength fiber lasers, ultra-fast mode-locked fiber laser, as well as the optical wideband chaos source, which have very good application prospects in the FOSN. Meanwhile, intelligent management techniques for the FOSN including wideband spectrum demodulation of the sensing signals and real-time fault monitoring of fiber links are presented. Moreover, several typical applications of the FOSN are also discussed, such as the fiber optic gas sensing network, fiber optic acoustic sensing network, and strain/dynamic strain sensing network.

Recent Advances in Spectroscopic Gas Sensing With Micro/Nano-Structured Optical Fibers

With micro-and nano-structured optical fibers,parts-per-million to parts-per-trillion level gas detection has been demonstrated for a range of gases such as methane,acetylene,ethane,carbon monoxide,hydrogen,and oxygen.We review the recent development in optical fiber gas cells and gas detection systems based on direct absorption,photothermal,photoacoustic,and stimulated Raman spectroscopies.