Nanocrystalline cerium oxide coated fiber optic gas sensor

A clad-modified fiber optic sensor with nanocrystalline CeO₂ is proposed for gas detection. As-prepared and annealed CeO₂ (500 °C) samples have been used as gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia, ethanol and methanol gases (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the gas concentration. The characteristics of the sensor are also studied for gas selectivity. The time response characteristics of the sensor are reported.     

Long-gauge length embedded fiber optic ultrasonic sensor for large-scale concrete structures

A fiber optic ultrasonic sensor based on Fizeau interferometer has been developed and demonstrated. A helium–neon laser light source with wavelength 0.6328 μm is used in our experiment. A special feature is its Fizeau configuration, which enables one to eliminate much undesirable noise by combining both the reference arm and the sensing arm within the same length of fiber. The dynamic response model of photo-elastic effect of ultrasonic wave and optical fiber is established. The fiber optic ultrasonic sensor experimental results are obtained and compared with the convenient PZT transducer.     

Data-dependent system approach for strain measurement in interferometric fiber optic sensor

A fiber optic interferometric sensor (Mach–Zehnder type) based on data-dependent system is presented for strain measurement. The interferogram recorded from the interferometer has been digitized and characterized by means of an autoregressive model. The phase change due to the measurand has been obtained from the self coherence function of the interferogram. The modulation of group delay and dispersion are obtained from the phase curve. Results for applied strain in the range of 5–10 μ strain are presented.     

Lead-insensitive fiber optic pH sensor and performance under bending

We have designed and tested a lead-insensitive fiber optic pH sensor that is based on the absorption of an indicator dye immobilized in a polymer bead. The fiber optic pH sensor uses two wavelengths; one senses the change in absorption of the indicator dye and the other provides a reference signal. In a view to desired time modulation and the dual wavelength time division multiplexing, we used light emitting diodes for sources, a phototransistor for the detector, and electronics process the detected signal. The sensor has demonstrated fast response, repeatable calibration, reversibility, and stability. This inexpensive device may also be used during bending of the optical fiber for applications in the field.     

ZnO thin film on side polished optical fiber for gas sensing applications

In this work, thin ZnO films have been produced by pulsed laser deposition on side-polished fiber for optical gas sensor applications. The influence was investigated of the processing parameters, such as substrate temperature and oxygen pressure applied during deposition, on the sensitivity to ammonia of the sensing element. A shift of the spectral position of the resonance minimum to the longer wavelengths was observed at room temperature for the sample prepared at 150 °C substrate temperature and 20 Pa oxygen pressure. Spectral changes in the range 0.16-1.13 nm for NH₃ concentrations between 500 and 5000 ppm were also observed.     

Study of fiber optic sugar sensor

Over the last two decades, the fiber optic technology has passed through many analytical stages. Some commercially available fiber optic sensors, though in a small way, are being used for automation in mechanical and industrial environments. They are also used for instrumentation and controls. In the present work, an intensity-modulated intrinsic fiber optic sugar sensor is presented. This type of sensor, with slight modification, can be used for on-line determination of the concentration of sugar content in sugarcane juice in sugar industry. In the present set-up, a plastic fiber made of polymethylmethacrylate is used. A portion of the cladding (1 cm, 2 cm, 3 cm) at the mid-point along the length of the fiber is removed. This portion is immersed in sugar solution of known concentration and refractive index. At one end of the fiber an 850 nm source is used and at the other end a power meter is connected. By varying the concentration of sugar solution, the output power is noted. These studies are made due to the change in refractive index of the fluid. The device was found to be very sensitive which is free from EMI and shock hazards, stable and repeatable and they can be remotely interfaced with a computer to give on-line measurements and thus become useful for application in sugar industries.     

纳米级光纤位移传感器

介绍利用高斯光束干涉测微小位移的方法,利用该方法设计了纳米级光纤位移传感器,测试了该传感器的位移响应与频率响应.     

Sensitivity-variable fiber optic pressure sensors using microbend fiber gratings

We report on sensitivity control of fiber optic sensors using microbend long-period fiber gratings. By tuning the phase difference between a pair of periodically aligned rod arrays that sandwiches a single-mode fiber, we can change the coupling strength of the core mode with radiating cladding modes, resulting in variable pressure sensitivity of the transmission power through the fiber. This technique enables control of the measurable range of pressure. When the phase difference is shifted from π toward 0, the measurable range is expanded from 1.7 to 3.3 N/cm and higher using a light-emitting diode as an input light source.     

Modeling and simulation of polarization errors in Sagnac fiber optic current sensor

Sagnac fiber optic current sensor (S-FOCS) is a kind of optical interferometer based on Sagnac structure, optical polarization states of sensing light wave in Sagnac fiber optic current sensor are limited. However, several factors induce optical polarization error, and non-ideal polarized light waves cause the interference signal crosstalk in sensor, including polarizer, quarter-wave retarder, splice angular, birefringence and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. To clarify characteristics of optical polarization error in fiber optic current sensor, we analyze the evolution process of random optical polarization state, linear optical polarization state and circular optical polarization state in Sagnac fiber optic current sensor by using Poincare sphere, then, build optical polarization error models by using Jones matrix. Based on models of polarization state in Sagnac fiber optic current sensor, we investigate the influence of several main error factors on optical polarization error characteristics theoretically, including extinction ratio in polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and polarization maintaining fiber. Finally, we simulate and quantify nonreciprocal phase shift to be detected in fiber optic current sensor related with optical polarization errors. In the end, we demonstrate S-FOCS in test. The results show that transfer matrix errors are induced by inaccurate polarization properties during polarization state conversion, then, the stability and accuracy of the S-FOCS are affected, and it is important to control the polarization properties at each step of the polarization state conversion precisely.     

Analysis of refractometric fiber optic state-of-charge (SOC) monitoring sensor for lead acid battery

In situ monitoring of the state of charge (SOC) of lead acid battery is important to understand the residual electrical energy. Usage of battery reduces the charge content of the active electrolyte which in turn changes its refractive index. This paper reports refractometric fiber optic sensor developed for on-line monitoring of SOC. The SOC is monitored during discharging phases of the battery using the developed fiber optic sensor probe along with terminal voltage, temperature and depth of discharge using a LABVIEW based data acquisition system. The paper gives the working principle, design and construction details, results and calibration of the fiber optic sensor (FOS) probe. The in situ monitoring capability of the developed FOS is demonstrated in comparison with the contemporary off-line methods of specific gravity and terminal voltage measurements.     

Total dissolved solids estimation with a fiber optic sensor of surface plasmon resonance

In this paper, surface plasmon spectra of ion influence was investigated by using a fabricated fiber optic sensors, then spectrum subtraction of ion and non-ionic solutions were developed for field applications of total dissolved solids (TDS) estimation. We confirmed the SPR spectral difference between seven ionic and three non-ionic liquid samples, that for the same refractive index, resonance wavelength in SPR spectrum is much higher for ionic samples than that in the case of non-ionic ones due to the ions influence. The positive correlation of ion content and extra resonance wavelength shift has been established for TDS estimation in water. With three groups of water samples investigation and field testing, the proposed SPR technique showed a good performance comparable to the conductivity method.     

纳米ZnO薄膜的光致发光性质

利用溶胶－凝胶法制备了纳米ZnO薄膜,室温下测量了样品的光致发光谱(PL)、吸收谱(ABS)、X射线衍射谱(XRD)．X射线衍射(XRD)的结果表明：纳米ZnO薄膜呈多晶状态,具有六角纤锌矿晶体结构和良好的C轴取向．观察到二个荧光发射带,中心波长分别位于395 nm的紫带、524 nm的绿带和450 nm附近的蓝带．证实了纳米ZnO薄膜绿光可见发射带来自氧空位(VO)形成的浅施主能级和锌空位(VZn)形成的浅受主能级之间的复合;450 nm附近的蓝带来自电子从VO的浅施主能级到价带顶或锌填隙(Zni) 到价带顶或导带底到VZn的浅受主能级的复合．     

Fiber Bragg grating sensor for petroleum hydrocarbon leak detection

A novel type of fiber optic Bragg grating sensor for petroleum hydrocarbon leak detection is presented. The sensor structure includes attached to the fiber a polymer member, which reversibly expands in hydrocarbon presence and strains the fiber section with the Bragg grating inside. A shift of the grating Bragg wavelength due to fiber strain is more than 2 nm for 20-min gasoline influence, which significantly exceeds a shift due to possible environmental temperature variation.     

Sensing ammonia with ferrocene-based polymer coated tapered optical fibers

Abstract

The application of ferrocene-based polymers as variable index materials is discussed. The refractive index of thin film of a particular polymer known as poly(methylphenylsilyeneferrocenylene) is examined during exposure to ammonia, nitrous oxide, nitric oxide, nitrogen, carbon dioxide, carbon monoxide, and argon. A maximum of 9% deviation in the refractive index of the polymer upon exposure to ammonia is observed. The theory of operation and fabrication of polymer-coated tapered optical fiber gas sensors are explained. Experimental data is presented showing qualitative response to ammonia and other gases.     

Sensing ammonia with ferrocene-based polymer coated tapered optical fibers

The application of ferrocene-based polymers as variable index materials is discussed. The refractive index of thin film of a particular polymer known as poly(methylphenylsilyeneferrocenylene) is examined during exposure to ammonia, nitrous oxide, nitric oxide, nitrogen, carbon dioxide, carbon monoxide, and argon. A maximum of 9% deviation in the refractive index of the polymer upon exposure to ammonia is observed. The theory of operation and fabrication of polymer-coated tapered optical fiber gas sensors are explained. Experimental data is presented showing qualitative response to ammonia and other gases.     

Shaft runout inspection by a fiber optic displacement sensor

A reflective fiber optic displacement sensor has been developed and calibrated to gauge form and axis position of shafts during rotation. A technique has been implemented to determine the deviation of the actual shaft form from its nominal circular cross section (the off-round error) and the departure of the rotation axis from the geometric axis (the eccentric error). The sensor is simple, has acceptable accuracy for applications to mechanical engineering, is capable of monitoring shafts during rotation, and has potential for gauging parts on the production line.     

Temperature-independent bending sensor with tilted fiber Bragg grating interacting with multimode fiber

A new type fiber bending sensor based on a tilted fiber Bragg grating (TFBG) interacting with a multimode fiber (MMF) is presented. The sensing head is formed by insertion of a small section of MMF between a single-mode fiber (SMF) and the TFBG. The average reflective power in the cladding modes decreases with the increase of curvature. The measurement range of the curvature from 0 to 2.5 m⁻¹ with a measurement sensitivity of −802.4 nW/m⁻¹ is achieved. The proposed sensor is also proved as temperature-independent from the experimental investigation.     

Fiber optic intensity sensor referenced with a virtual delay line

In this work a self-referencing fiber optic intensity sensor using virtual instrumentation is presented. To ensure higher flexibility and dynamic optimization, the use of an optical fiber delay line or an electrical delay line is avoided by implementing a delay line in the virtual domain, preserving the self-referencing and sensitivity characteristics of the proposed optical intensity sensing structure. Results are presented where displacement is measured with an 18 μm resolution demonstrating the concept feasibility.     

Resonantly excited ZnO nanowires for fabrication of high sensitivity gas sensor

A novel approach for gas sensing based on mechanical resonance of ZnO nanowires is reported. For this purpose, ZnO nanowires were grown between comb-like electrodes using a novel oxygen plasma treatment approach. Then gas measurements were carried out at different agitating frequency. Results show an improvement in gas sensitivity of resonantly excited ZnO nanowires. Our results open up a promising approach to fabricate high sensitivity gas sensor. Also we have introduced an alternative frequency modulation gas detection method here.     

光纤水听器探头技术研究

光纤水听器的探头技术是光纤水听器系统的基础，本给出了国内外光纤水听器探头设计的一些典型方案。并对它们进行对比分析。就光纤水听器探头技术的几个重要参数指标进行了评价。