Optical coherent detection Brillouin distributed optical fiber sensor based on orthogonal polarization diversity reception

In Brillouin distributed optical fiber sensor, using optical coherent detection to detect Brillouin scattering optical signal is a good method, but there exists the polarization correlated detection problem. A novel detecting scheme is presented and demonstrated experimentally, which adopts orthogonal polarization diversity reception to resolve the polarization correlated detection problem. A laser is used as pump and reference light sources, a microwave electric-optical modulator (EOM) is adopted to produce frequency shift reference light, a polarization controller is used to control the polarization of the reference light which is changed into two orthogonal polarization for two adjacent acquisition periods. The Brillouin scattering light is coherently detected with the reference light, and the Brillouin scattering optical signal is taken out based on Brillouin frequency shift. After electronic processing, better Brillouin distributed sensing signal is obtained. A 25-km Brillouin distributed optical fiber sensor is achieved.     

On‐chip stimulated Brillouin Scattering for microwave signal processing and generation

Demonstration of continuously tunable delay, low‐noise lasers, dynamically controlled gratings, and optical phase shifting using the stimulated Brillouin scattering (SBS) process has lead to the emergence of SBS as a promising technology for microwave photonics. On‐chip realization of SBS enables photonic integration of microwave photonic signal processing and offers significantly enhanced performance and improved efficiency. On‐chip stimulated Brillouin scattering is reviewed in the context of slow‐light based tunable delay, low‐noise narrow linewidth lasers and filtering for integrated microwave photonics. A discussion on key material and device properties, necessary to enable on‐chip Brillouin scattering using both the single‐pass and resonator geometry, is presented along with an outlook for photonic integration of microwave signal processing and generation in other platforms.     

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.     

Dual-source distributed optical fiber sensor for simultaneous temperature and strain measurements

A dual-source distributed optical fiber sensor system with combined Raman and Brillouin scatterings is designed for simultaneous temperature and strain measurements. The optimal Raman and Brillouin signals can be separately obtained by adjusting the powers of the two sources using an optical switch. The temperature and strain can be determined by processing the optimal Raman and Brillouin signals. The experimental result shows that 1.7 ?C temperature resolution and 60-με strain resolution can be achieved at a 24.7-km distance.     

Brillouin scattering of light by spin waves in ferromagnetic nanorods

We report the investigations of spin wave modes of arrays of Ni and Co nanorods using Brillouin light scattering. We have revealed the significant influence of spin wave modes along the nanorod axis in contrast to infinite magnetic nanowires. Unusual optical properties featuring an inverted Stokes/anti-Stokes asymmetry of the Brillouin scattering spectra have been observed. The spectrum of spin wave modes in the nanorod array has been calculated and compared with the experiment. Experimental observations are explained in terms of a combined numerical–analytical approach taking into account both the low aspect ratio of individual magnetic nanorods and dipolar magnetic coupling between the nanorods in the array. The optical studies of spin-wave modes in nanorod metamaterials with low aspect ratio nanorods have revealed new magnetic and magneto-optical properties compared to continuous magnetic films or infinite magnetic nanowires. Such magnetic artificial materials are important class of active metamaterials needed for prospective data storage and signal processing applications.     

Stimulated Brillouin scattering frequency-domain analysis in a single-mode optical fiber for distributed sensing

A numerical and experimental analysis of the stimulated Brillouin scattering in a single-mode optical fiber for distributed sensing applications is carried out in the frequency domain. The theoretical model describing the Brillouin interaction is solved by taking into account the temporal dynamics of the acoustic wave that is involved. The simulations and the experimental results reveal the role played by the ac component of the acoustic wave, which is responsible for significant changes of the small-signal stimulated Brillouin scattering transfer function that occur when the modulation frequency rises above the natural Brillouin gain spectrum linewidth. One should take these effects into account to perform accurate signal processing of frequency-domain signals in high-resolution distributed sensing applications.     

光学单池中受激布里渊散射的双光束共轴放大

介绍了一种在单池中实现受激布里渊散射双光束共轴放大的方法,能够在单一光学池中同时实现受激布里渊散射的产生和放大.相比于传统的双池放大技术,这种方法具有结构简单、信号损失小的优点.对于激光雷达等无法采用双池放大的实际应用领域,单池放大技术更是一种必要的方法. 关键词： 受激布里渊散射 放大 光学单池     

布里渊动态光栅原理及其在光纤传感中的应用

自从2007年布里渊动态光栅被首次提出用于实现光存储以来,该技术得到了国际上的广泛关注和研究.布里渊动态光栅本质上是由相干声波场激发的折射率光栅,一般情况下两束抽运光(频率差等于光纤的布里渊频移)以相同的偏振态从光纤两端注入到光纤中,通过受激布里渊散射效应激发出相干声波场,即形成布里渊动态光栅.光纤布里渊动态光栅因具有全光产生、参数灵活可控的优点,已被广泛研究应用于光纤传感、光纤特性表征、光存储、全光信号处理、微波光子学和高精度光谱分析等.本文分析布里渊动态光栅产生和探测原理,重点探讨在高性能分布式光纤传感上的应用,这些应用包括高灵敏度温度和应变分布式传感、温度和应变同时解调、分布式横向压力传感、分布式静压力(气压或液压)传感、高空间分辨率分布式传感和高精度光谱分析.     

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。     

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.     

Accuracy enhancement in Brillouin scattering distributed temperature sensor based on Hilbert transform

The scattering optical signal of OTDR based Brillouin scattering distributed sensor is very weak and have a frequency width of several decades megahertz, so it is hard to perform the traditional analogue coherent demodulation. A novel optical coherent detection based on Hilbert transform is presented here. In detail, Brillouin backscattering light is coherent detected with the reference light, which is modulated by microwave electric optical modulator to produce frequency-adjustable light, then the detected photocurrent signal is demodulated by digital signal processing based on Hilbert transform, and at last the distributed sensing signal with better S/N ratio is gained, which can enhance the performance of the sensor. The simulation and experimental results of the detection method are given.     

Temperature and strain dependence of the power level and frequency of spontaneous Brillouin scattering in optical fibers

The strain dependence of the optical power of Brillouin scattering in optical fibers has been measured for the first time to our knowledge. Together with measurements of the dependence of Brillouin power on temperature and the variation of Brillouin frequency with temperature and strain, we demonstrate, for what we believe to be the first time, the feasibility of a simultaneous temperature and strain sensor based on spontaneous Brillouin scattering.     

A novel approach for simultaneous millimeter wave generation and high bit rate data transmission for Radio over Fiber (RoF) systems

We propose a novel method for simultaneous transmission of OC-192 (9.95328 Gbps) digital data and 60 GHz RF generation in a Standard Single Mode Fiber (SSMF) link utilizing Stimulated Brillouin Scattering (SBS). The system comprises of a 1550 nm DFB Laser diode, Mach Zehnder modulator (MZM), 50 km SSMF and Optical receiver. The receiver includes laser diode for optical pump, a regenerator for data retrieval and a RF bandpass filter for RF generation. This system requires minimum number of RF and optical components for the generation of 60 GHz RF. The remotely generated 60 GHz RF signal may be used for wireless transmission of data. The entire link is simulated in Optisystem software to analyze the system performance.     

基于宽带光源和自外差检测的布里渊光时域反射温度传感系统

为简化系统结构、减小相干瑞利噪声对系统性能的影响,提出了一种采用宽带光源的瑞利和布里渊散射自外差检测布里渊光时域反射温度传感系统.分析了瑞利和布里渊自外差检测原理,研究了布里渊频移和自外差信号功率与光纤温度和应变的关系.设计并搭建采用宽带光源的自外差检测布里渊光时域反射温度传感系统,获得了常温下沿光纤分布的自外差信号功率谱及不同温度时加温段光纤的功率谱,验证了布里渊频移和自外差信号相对功率变化随温度的线性增加关系.通过实验数据获得的布里渊频移和相对功率变化的温度系数分别为1.07±0.01MHz/℃和(0.37±0.09)%/℃.本文的研究结果为基于瑞利和布里渊自外差检测布里渊光时域反射传感系统的温度和应变同时测量提供了理论和实验依据.     

提高布里渊光时域反射应变仪测量空间分辨力的等效脉冲光拟合法

由于探测光脉冲宽度受到限制,布里渊光时域反射仪(BOTDR)在对光纤上的应变进行分布式测量时,空间分辨力只能达到1 m。针对布里渊光时域反射仪单次采样接收背向布里渊散射信号(BBS)需要一定的时间,提出了基于等效脉冲光的多洛仑兹拟合法以提高其应变测量的空间分辨力。该方法将探测光脉冲在布里渊光时域反射仪完成单次采样所需的时间上进行积分,将积分函数作为等效脉冲光的表达式,再根据等效脉冲光的形状将布里渊光时域反射仪接收到的背向布里渊散射谱(BBS)细分,并对它进行多洛仑兹迭代拟合,准确求得每个细分布里渊散射谱的中心频率,进而利用光纤中布里渊频移与应变的对应关系,得到光纤中与细分布里渊散射谱对应的细分光纤单元上的应变情况。实验结果表明,利用这种方法,可使布里渊光时域反射仪应变测量的空间分辨力提高至0.05 m。     

液芯光纤中基于多线抽运调制的带宽可控平顶布里渊增益谱

提出在CS₂/CCl₄混合介质液芯光纤中利用多线抽运调制 技术实现带宽可控平顶布里渊增益谱的方法, 理论研究了抽运光谱线间距、谱线强度和芯液介质混合比对布里渊增益谱的影响, 得到了带宽可控平顶增益谱的条件. 结果表明, 采用一个强度或相位调制器, 基于单频和多频调制技术产生2–9条抽运光谱线, 通过控制谱线间距和各谱线强度比, 并改变CS₂体积分数, 获得了增益带宽在50 MHz–2 GHz 范围内可控的平顶增益谱. 该方法操作简便、带宽调控范围大, 可用于高增益低畸变布里渊放大, 满足微弱光信号探测和慢光系统的应用需求. 关键词： 受激布里渊散射 布里渊增益谱 多线抽运调制 液芯光纤     

Stimulated Brillouin scattering in highly birefringent microstructure fiber: experimental analysis

We report on an experimental analysis of stimulated Brillouin scattering (SBS) in a 20-m-long highly birefringent microstructure fiber for sensing applications. In particular, an experimental setup based on Brillouin optical frequency-domain analysis, operating at a wavelength of 1550 nm, has been employed in order to analyze the distribution of Brillouin frequency shift along the fiber, as well as to study the dependence of Brillouin frequency shift on optical polarization, temperature, and strain. Our results indicate that, for any fixed polarization, the fiber has a dual-peaked Brillouin spectrum. A study about the origin of these two peaks is presented.     

基于微波电光调制的布里渊光时域分析传感器

针对布里渊光时域分析分布式传感原理和受激布里渊散射的特点,应用微波电光调制分布反馈式半导体激光器产生频移可调的探测光,和传感光纤中相反方向传输的脉冲激励光进行受激布里渊散射作用,当探测光和激励光的频率差在布里渊频移附近时,频移探测光和激励光产生受激布里渊散射,通过改变探测光的频移值,检测探测光功率信号,可得到沿光纤各处的布里渊频移,再利用布里渊频移和应变（或温度）的关系,计算得到沿光纤分布的传感量。设计了基于微波电光调制的布里渊光时域分析传感器实验系统,实现了25km的分布式温度传感,达到5m的空间分辨力和3℃的温度分辨力。     

Effect of Brillouin slow light on distributed Brillouin fiber sensors

The effect of Brillouin slow light on distributed Brillouin fiber sensors (DBFSs) is studied. We demonstrate Brillouin slow light for a 1.2 ns pulse with peak powers (PS) from 3.3 to 56.2 mW on depletion of the pump power (PP) ranging from 1.3 to 83.2 mW in conventional optical fibers (SMF-28). Experiments show that, when pump power depletion is not negligible, for a given PP the Brillouin gain and delay time of a pulse decrease when PS increases in a long (> or =10 km) sensing fiber. The optimum pump beam depletion resulting from strong interaction of the pump and the probe in the fiber provides accurate temperature and strain information at a high spatial resolution. Our study reveals that at low PP the spatial resolution error caused by the pulse delay for a DBFS with centimeter spatial resolution is less than 5% of the pulse length.     

Distributed strain measurement with millimeter-order spatial resolution based on Brillouin optical correlation domain analysis

Distributed strain sensing with millimeter-order spatial resolution is demonstrated in optical fibers based on Brillouin optical correlation domain analysis. A novel beat lock-in detection scheme is introduced to suppress background noises coming from the reflection of Brillouin pump waves. The Brillouin frequency shifts of 3 mm fiber sections are successfully measured with a theoretical spatial resolution of 1.6 mm.