Synthetic-heterodyne interferometric demodulation

A new interferometric demodulation technique is described. This technique employs phase swept multicarrier demodulation (synthetic-heterodyne) to optimize the interferometer output.     

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms, so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors, and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system, so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the fre- quency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the fre-quency characteristics.     

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.     

一种光纤传感器温度与应变同时解调的方法

文章分析了一种利用外差检测所得微波信号的电场振幅和频率来计算后向布里渊散射光功率及频移的方法.该方法通过对功率较强的微波信号进行数值拟合,利用得到的直流分量和交流分量计算出后向散射光功率、频移及其随温度、应变变化的系数矩阵.数值结果表明,温度、应变的解调精度分别为1℃、100 με,但也受到一定采样频率的限制.     

干涉型光纤传感器偏振衰落动态补偿技术

为了消除单模光纤制作的光纤传感器常会因外部环境扰动而引起相位衰落和偏振衰落,通过改进传统的马赫-泽德干涉仪,利用高频振荡的PZT结合相位生成载波零差解调电路用来补偿相位衰落,引入一个可随干涉信号的幅值变化旋转的半波片来调整输出的干涉信号,据此可实现偏振衰落的动态补偿.通过理论分析可以得出由偏振衰落造成的信号幅度波动不大于3dB.     

基于EDFA的分布式光纤喇曼温度解调技术

为了消除掺铒光纤放大器的放大自发辐射噪声对分布式光纤温度传感器测温精度的影响,采用精确的修正公式进行温度解调是一种有效手段。通过分析掺铒光纤放大器的放大自发辐射噪声对系统产生的影响,并将计算的中间结果代入理论公式获得了修正后的温度解调公式。实验中分别采用理论公式和修正公式对温度进行分布式测量并获得了实验数据。结果表明,修正后的温度解调公式有效补偿了掺铒光纤放大器噪声引起的误差,并显著提高了系统的信噪比和测温精度;修正公式可将系统的整体测温精度提高到1℃～2℃;此外,实验中观察到多模光纤中喇曼背向自发散射同样会出现放大现象,这与单模光纤中的情形类似,且放大喇曼自发散射依然具有理想的温度效应。     

All-digital demodulation system of interferometric fiber optic sensors using an improved PGC algorithm based on fundamental frequency mixing

In this paper,the optimum supercontinuum(SC)spectrum generation in a dispersion decreasing fiber is presented.Three normalized parameters for the pump pulse and SC fiber are introduced.It is found that the shape of an SC spectrum is uniquely specified by the input soliton order,the normalized dispersion slope and the normalized effective fiber length.For a pumping condition with a given input soliton order and a given normalized dispersion slope,by optimizing the normalized effective fiber length,the residual spectral peak in the SC spectrum can be suppressed effectively,and a broad SC spectrum with optimum spectral flatness can be obtained.     

Analysis of an interferometric optical fibre detection technique applied to silicon vibrating sensors

A simple and accurate analysis of a single-mode optical fibre interferometric displacement detection technique is resented. This analysis is in good agreement with experimental measurements, and shows that angular alignment between the fibre and the sensor is the most critical parameter.     

Counting wavelength demodulation of FBG sensors

Measuring amplitude of signal is the usual method in wavelength demodulation of fiber Bragg grating (FBG) sensors recently. This method is easy to be disturbed and has low precision. In this paper, a novel counting wavelength demodula- tion scheme of FBG sensors using a high birefringent fiber (HBF) loop mirror is reported. This demodulator has simple structure, high precision, cheap price and convenient use. The resolution of the loop mirror device with a HBF of 30 meters long is 0.067 nm. For a center wavelength of FBG of about 1550 nm and a 40 nm shift range of its reflection wavelength, the relative error of measurement is only ± 0.001. This wavelength demodulation device has significance for widespread application of FBG sensors.     

Coherence multiplexing of fiber-optic interferometric sensors

This paper describes a method of multiplexing several optical signals onto a single spatial channel (e.g., a single-mode fiber) using a short coherence length continuous wave light source. Several system configurations which utilize this technique are proposed, and some design considerations are discussed. Experimental results for a single sensor and receiver are presented and compared with theoretical predictions.     

Multiplexing of nonlinear fiber-optic interferometric sensors

The scheme is demonstrated with a three-sensor array consisting of magnetic-field, pressure, and displacement sensors exhibiting resolutions at 1 Hz of 20 μOe/√Hz (limited by ambient noise), 0.1 kPa/√Hz, and 30 nm/√Hz, respectively. Multiplexing is accomplished by dithering each transducer at a different frequency and using parallel phase-sensitive detectors (PSD) at the interferometer output to demultiplex the information. A single Mach-Zehnder interferometer driven by a single unmodulated laser was used. Factors affecting the performance of the multiplexing scheme, including interferometric demodulation technique, PSD performance, and nonlinear transduction mechanism, are discussed     

光纤光栅传感器的解调与复用技术

光纤光栅传感器以其波长编码的独有优势适用于准分布式测量网络.文章介绍了光纤光栅传感器的解调方法,分析了其工作原理、性能和特点.提出了几种常用的光纤光栅复用方案,比较了它们的优缺点和组网规模,并指出准分布式传感网络的发展前景.     

Polarization fading in fiber interferometric sensors

Mach-Zehnder interferometer sensors fabricated with conventional nonpolarization-preserving fibers are subject to polarization fading caused by temperature variations and minor positional changes in the sensor. For such sensors, we calculate the probability of a given decrease in sensitivity and in signal-to-noise ratio due to fading assuming the polarization of the light in the signal and reference legs is uncorrelated and drifts randomly. The resultant reduction of the signal-to-noise ratio may exceed 10 dB 10 percent of file time and exceed 20 dB more than 2 percent of the time.     

Latest development of fiber-optic fibry-Perot interferometric sensors

简单介绍了光纤F-P传感器的工作原理,然后根据光纤F-P传感探头的制作方法进行分类,从传感特性的角度阐述了当前F-P传感器的研究方向和现状,最后给出了其发展趋势.     

Proposed interferometric optical isolator

This correspondence describes the concept of a non-reciprocal transmission isolator or four-port circulator consisting of an anisotropic index of refraction element inside the perimeter of a traveling-wave (ring) interferometer. The potential advantages of this device with regard to feedback power rejection capability and rejection ratio are discussed.     

Optimizing fiber coatings for interferometric acoustic sensors

The pressure sensitivity of the phase of light propagating in an optical fiber is studied both analytically and experimentally. The analysis, which takes into account the exact composition and geometry of multilayer fibers, is utilized to identify coating properties which optimize the fiber acoustic sensitivity. In order to predict the fiber acoustic sensitivity, the elastic parameters of commonly used coating materials, thermoplastics, and UV curable elastomers have been studied in bulk samples as a function of frequency (10^{2}-10^{4}Hz) and temperature (0-35degC). The analytically predicted frequency dependence of the acoustic sensitivity is found to be in agreement with that obtained experimentally from fibers with coatings of various materials.     

Multiplexing of interferometric sensors using phase carrier techniques

This paper demonstrates the multiplexing of fiber-optic interferometric sensors using a CW phase generated carrier technique. The technique employs modulated diode laser sources at different carrier frequencies, nearly balanced interferometers (∼4-cm path difference), and phase generated carrier demultiplexing demodulation. This approach leads to a simple all-passive sensor array which has intrinsically low crosstalk. The system is analyzed in terms of shot noise performance and crosstalk. An experimental all optical implementation of a four sensor array was demonstrated; both the single sensor and multisensor arrays were limited by the laser phase noise to a sensitivity ofsim 18 murad/sqrt{Hz}. Crosstalk between individual channels was better than -60 dB and crosstalk between three sensors and the test sensor was better than -55 dB. In the absence of laser phase noise the demodulator/demultiplexer demonstratedsim 2-murad performance with both single sensor and four element array operation.     

Multiplexing of interferometric sensors using phase-generated carrier techniques

The multiplexing of four interferometric sensor outputs on a single optical fibre using a phase-generated carrier technique is demonstrated. Low crosstalk ( ? 60 dB) and high performance (minimum detectable phase shifts of 2?18 ?rad) were achieved with this configuration. This technique is expandable to large numbers of sensors.     

Interrogation of fibre-optic interferometric sensors usingacousto-optic tunable filter

A new technique for the interrogation of interferometric-based fibre-optic sensors using an acousto-optic tunable filter (AOTF) is demonstrated The scheme involves frequency shift keying (FSK) of the RF drive to the AOTF to track the shift of a single fringe peak from an interferometric sensor. Experimental results are presented for a Fizeau interferometer. The technique provides high accuracy, plus a large unambiguous tracking range free from interruptions     

Multipulse interferometric frequency-resolved optical gating

We review multipulse interferometric frequency-resolved optical gating (MI-FROG) as a technique, uniquely suited for pump-probe coherent spectroscopy using amplified visible and near-infrared short-pulse systems and/or emissive targets, for time-resolving ultrafast phase shifts and intensity changes. Application of polarization-gate MI-FROG to the study of ultrafast ionization in gases is presented