A new method to eliminate the influence of the backward defect infection and the position-dependent of the coefficient on distributed Brillouin fiber sensor

Two theoretical problems associated with the measurement of temperature or strain from the normalized power of Brillouin signal in a distributed fiber sensor are studied. One problem is the position-dependent of the coefficient relating the Brillouin power to the local temperature or strain. The other problem is the backward infection of the defect (local temperature or strain change). These two problems will degrade the measurement accuracy of a distributed Brillouin fiber sensor by changing the distribution of pump power. To eliminate these two problems, new reference functions are proposed to normalize the Brillouin signal. Simulation results by using fourth-order Runge-Kutta algorithm show that these new reference functions can eliminate the influence of these two problems on distributed Brillouin fiber sensor.     

拉曼放大布里渊光时域分析系统非局域效应

应用包含探测光、布里渊泵浦光及拉曼泵浦光相互作用理论模型,数值分析了基于拉曼放大的长距离布里渊光时域分析仪非局域化特性。结果表明:非局域化随探测光及拉曼泵浦功率增加而恶化;通过频分复用(将具有不同布里渊频移的光纤拼接)及时分复用技术(同时对布里渊泵浦及探测光进行脉冲调制),可有效缩短布里渊泵浦与探测光的作用距离,达到较理想的抑制非局域效应结果。     

Polarization dependence of angle-resolved photoemission spectroscopy of graphite

We have used variable polarization synchrotron radiation to map the valence band electronic structure of graphite by angle-resolved photoemission spectroscopy (ARPES). The experimental results with two orthogonal linear polarization of light signifies the contribution of either even or odd symmetry with respect to the crystal mirror plane towards the photoemission intensity. The σ₁ and σ₂ valence bands show odd reflection symmetry while the π valence band shows even symmetry with respect to the mirror plane. The measured ARPES spectrum using left and right circular polarized lights shows asymmetry in intensity around M point of the Brillouin zone, which ultimately mimicking different partial wave character of σ₁ and σ₃ bands.     

Bi-directional dual-wavelength Brillouin lasing in a hybrid fiber ring cavity

In this paper, a novel Brillouin fiber laser (BFL) is proposed based on the hybrid fiber ring cavity composed of two types of fibers with different Brillouin shifts. Single mode fiber (SMF) and truewave fiber (TWF) are used in our experiments. Bi-directional dual-wavelength Brillouin lasing is achieved in the hybrid fiber ring cavity. The lasing lights along the two directions come from the Stokes waves generated in the two fibers, respectively, with different Brillouin shifts, however, they share the same fiber ring cavity. The BFL based on the hybrid fiber ring cavity provides a simple possible way to realize Brillouin fiber optical gyroscopes (BFOGs) without lock-in effect.     

Power measurement of noise-initiated Brillouin scattering in optical fibers for sensing applications

We discuss the measurement of noise-initiated Brillouin scattered power in optical fibers and its application to distributed sensing systems. In particular, we consider the use of Brillouin scattering in the nonlinear regime, demonstrating a novel processing technique that compensates for the nonlinear growth of the scattered signals. The signal-to-noise ratio performance of this technique is evaluated, highlighting the importance of the noise contributed by the random statistics of the scattered field and yielding the conditions for optimum system operation.     

光纤移频分布式布里渊光纤传感技术

提出了一种利用布里渊光纤环形腔移频技术实现分布式光纤布里渊传感的方法.该方法基于布里渊光时域分析法原理,将一束单纵模运转激光器输出的激光分为两束|一束光入射布里渊光纤环形腔中产生窄线宽的受激布里渊散射光作为斯托克斯光,另一束光经过低频相位调制后作为泵浦光|斯托克斯光和泵浦光分别相向入射进入传感光纤,通过测量布里渊谱得到光纤温度或应变.利用该方法可将十几GHz的微波频率转化为兆赫信号频率进行探测处理,仅需一台激光器,因此系统结构简单、成本低,还可减小激光器频率波动对测量准确度的影响.实验验证了该方法的可行性.     

基于布里渊散射的分布式光纤传感技术

基于布里渊散射的分布式光纤传感技术是目前国内外研究的热点。其中基于时域定位的布里渊分布式光纤传感技术主要分为布里渊光时域反射和布里渊光时域分析两种。国内对基于布里渊光时域反射技术的分布式光纤传感技术的研究报道比较多。介绍了基于布里渊光时域分析技术的分布式光纤传感技术的研究现状,并对基于时域定位的两种传感技术进行了分析对比。总结了布里渊散射分布式光纤传感技术实用化存在的问题及可能的解决方法,指出了该传感技术进一步的发展方向。     

Absolute distance measurement by using modified dual-wavelength heterodyne Michelson interferometer

This study proposes a modified dual-wavelength heterodyne Michelson interferometer for measuring the absolute distance that can avoid the influence of wavelength drifts. This modified interferometer consists of two conventional Michelson interferometers. A standard plate is introduced in one arm of one Michelson interferometer. The phase differences of p- and s- polarization test lights in the two interferometers can be measured accurately by dual-wavelength heterodyne interferometry. Hence, the absolute distance can be determined by substituting the phase differences into special derived equations. Meanwhile, the test lights suffer from the same wavelength drift effect. Therefore, the negative effect caused by the drift can be offset, and the measurement stability can be significantly increased. The feasibility of this method was demonstrated with a measurement resolution of about 1.36 μm. Additionally, this method has a simple structure, easy operation and rapid measurement.     

Fast Brillouin Optical Fiber Sensor for Distributed Dynamic Measurement Based on Differential Double-Pulse

We demonstrate a high-spatial-resolution fast Brillouin optical time-domain analysis scheme based on frequency agility and differential double-pulse for distributed dynamic measurement. The frequency-agility probe wave is obtained from the second-order sideband of modulated light by using frequency-agility microwave signal from a wideband arbitrary waveform generator. The differential double-pulse technique is proposed to improve the spatial resolution while keeping the capability of dynamic measurement. In experiment, a spatial resolution of 20 cm is achieved by using a 52/50 ns differential double-pulse, and the distributed vibration measurement is demonstrated over a 50-m Panda fiber with a maximum vibration frequency of up to 50 Hz. With only five averages, the standard deviation of the strain accuracy is of 14 μV.     

光纤移频分布式布里渊光纤传感技术

提出了一种利用布里渊光纤环形腔移频技术实现分布式光纤布里渊传感的方法.该方法基于布里渊光时域分析法原理,将一束单纵模运转激光器输出的激光分为两束;一束光入射布里渊光纤环形腔中产生窄线宽的受激布里渊散射光作为斯托克斯光,另一束光经过低频相位调制后作为泵浦光;斯托克斯光和泵浦光分别相向入射进入传感光纤,通过测量布里渊谱得到...     

Effect of the finite extinction ratio of an electro-optic modulator on the performance of distributed probe-pump Brillouin sensor systems

The effect of the finite extinction ratio of an electro-optic modulator (EOM) on the Brillouin frequency measurement of a distributed Brillouin-based fiber optic sensor is studied. An EOM with a finite extinction ratio limits the application of Brillouin optical time domain analysis in a distributed Brillouin-based fiber optic sensor. This results in confusion in specifying the location of the strained region and in error in detecting the Brillouin frequency and hence in strain and temperature measurement.     

Dual-beam coaxial amplification system of stimulated Brillouin scattering based on polarization control technology

In the field of Brillouin lidar, it has very important significance to find one method that can amplify the Brillouin scattering signal in real time. One new-type Brillouin lidar detection system based on Nd:YAG pulsed laser and polarization control device is designed in this paper. The key point of this detection system is to have two pulsed coherent lights with same frequency, same polarization and same initial phase, of which one beam is taken as the detection wave for generating stimulated Brillouin scattering signal and the other beam is taken as pumping wave for real time and effective amplification of stimulated Brillouin scattering signal. This detection system mainly includes two pulsed lasers and one electro-optical polarization controller. The laser is mainly used to obtain the pulsed lights with same frequency and same phase, and the polarization controller is mainly used to change the polarization state of two coaxial beams to make them change into same polarization state from orthogonal polarization state thus to enable the pumping wave to amplify the backward stimulated Brillouin scattering signal. It is shown from the experimental results that the adoption of this new system can realize the effect of pumping amplification and can increase the signal to noise ratio to a certain extent.     

基于布里渊散射的结构应力光纤测试技术研究

本文通过分析一定功率的脉冲光射入光纤中的布里渊散射规律,介绍了分布式光纤测量测量轴向应力的基本原理。制作实验装置,测量单独的应变模型,分析散射回来的波形图,初步了解应力在光纤布里渊散射波谱上的图像特征。将应力作用于光纤的不同位置,对比它们与无应力作用诗所得到的散射波形之间的图像差异,研究其对光脉冲在光纤传输过程中的影响规律。结果表明,应力的作用大小,作用位置的不同都会对脉冲光的传播造成影响,主要在于影响布里渊散射的斯托克斯光和反斯托克斯光。本次研究所得可以为分布式光纤测量提供参考,为分布式光纤在测量微型形变的应用中有一定的促进作用。本次研究的创新点在于使用滑轮的方法,解决同等应力在分布光纤的不同位置作用效果。     

Comparison of the methods for discriminating temperature and strain in spontaneous Brillouin-based distributed sensors

A recently proposed method of measuring the two Brillouin frequencies in a multicompositional fiber core for unambiguously resolving temperature and strain in a distributed sensor is compared with the previously established technique of measuring the intensity and frequency of the single Brillouin peak in a standard single-mode fiber.     

Random‐access distributed fiber sensing

Optical sensing offers an attractive solution to the societal concern for prevention of natural and human‐generated threats and for efficient use of natural resources. The unprecedented properties of optical fibers make them ideal for implementing a ‘nervous system’ in structural health monitoring: they are small, low‐cost and electrically and chemically inert. In particular, the nonlinear interaction of stimulated Brillouin scattering allows for the distributed measurement of strain and temperature with tens of km range. In this work, a novel, radar‐inspired technique for random‐access Brillouin scattering‐based sensors is shown, making a significant step towards a real optical sensing nerve. The method selectively addresses each fiber segment as a distinct sensing element in a synaptic neuronal system. The measurement principle relies on phase‐coding of both the Brillouin pump and signal waves by a high‐rate, pseudo‐random bit sequence. Temperature measurements with 1 cm resolution are reported. The measurement range is scalable to several km.     

用碘分子共振吸收滤波器精确测量水中的布里渊散射频移

提出了一种基于分子共振吸收滤波技术的水中布里渊散射频移的探测方法——边缘探测方法。利用碘分子在水中的布里渊散射光谱范围内的两个对称的吸收峰,可以对光在水中的布里渊散射频移实现高精度的实时测量。对这一方法的原理进行了分析,给出了可用于实际测量的探测系统,并给出了用此系统得到的实验测量结果。还分析了测量系统的固有误差及测量灵敏度。结果表明,这一新方法与常规探测方法(如扫描干涉仪法)相比,具有实时性好、灵敏度高、测量精度高等突出的优点。     

Simultaneous temperature and strain measurement with combined spontaneous Raman and Brillouin scattering

We report on a novel method for simultaneous distributed measurement of temperature and strain based on spatially resolving both spontaneous Raman and Brillouin backscattered anti-Stokes signals. The magnitude of the intensity of the anti-Stokes Raman signal permits the determination of the temperature. The Brillouin frequency shift is dependent on both the temperature and the strain of the fiber; once the temperature has been determined from the Raman signal, the strain can then be computed from the frequency measurement of the Brillouin signal.     

一个新型的基于全光纤Mach-Zehnder干涉仪BOTDR系统

报道了新型的分布式传感测量布里渊光时域反射(BOTDR)系统.布里渊散射频移和强度均依赖于温度和应变,因此,BOTDR利用光纤中的自发布里渊散射作为测量信号可以实现分布式温度和应变测量.在BOTDR中,光源采用窄谱半导体激光器,并由声光调制器调制成脉冲光,经掺铒光纤放大器放大后,注入测试光纤以产生自发布里渊散射.利用双通Mach-Zehnder干涉仪分离光纤背向散射中的自发布里渊散射与瑞利散射信号,实现了自发布里渊散射的直接检测.实验结果表明基于全光纤Mach-Zehnder干涉仪BOTDR方案是可行的.     

A tunable frequency-decuple optoelectronic oscillator based on frequency comb and stimulated Brillouin scattering

An optically tunable frequency-decuple optoelectronic oscillator based on optical frequency comb (OFC) and stimulated Brillouin scattering has been proposed and theoretically analyzed. In the proposed structure, the OFC is generated using a cascaded Mach–Zehnder modulator and a dual-parallel Mach–Zehnder modulator (DPMZM), and multi-pump lights could be obtained instead of one pump. A quintuple Brillouin frequency shift oscillation signal generated by using Brillouin gain-loss compensation principle and carrier phase-shifted double sideband modulation is realized by using the DPMZM to double the oscillation frequency. As a consequence, a decuple frequency shift microwave signal is achieved. Profit from the wavelength-dependent nature of Brillouin frequency shift, a frequency-decuple signal at 10 \(f_{b}\) which could be tunable from 87.9750 to 94.4750 GHz by simply tuning the wavelength of the tunable laser source is obtained in theory.     

Dependence of the brillouin frequency shift on strain and temperature in a photonic crystal fiber

The dependence of the Brillouin frequency shift on strain in a photonic crystal fiber (PCF) was measured at a wavelength of 1320 nm for the first time to the authors' knowledge. Together with measurements of the dependence of the Brillouin frequency shift on temperature in the PCF, we demonstrate the feasibility of the highly precise simultaneous measurement of temperature and strain by use of the PCF in a distributed Brillouin sensing system with a spatial resolution of 15 cm.