光纤干涉仪中用于消除偏振衰落的平衡检测技术

针对单模光纤干涉仪两臂中光的偏振态受环境变化引起的信号衰落,提出了一种新的消偏振衰落方案.该方案基于单臂光纤干涉仪,通过对干涉仪的信号采用双路光电检测法,经过高通滤波器、平方器,将两路信号相加后,实现了干涉仪信号无偏振衰落输出.其实验结果与理论分析一致.     

温度和振动对光纤马赫-曾德干涉仪的影响与动态补偿研究

环境温度变化和振动会引起光纤马赫-曾德干涉仪两臂相差随机性变化,致使干涉仪输出不稳定.本文研究了自然条件下外界温度和振动对基于3×3耦合器干涉仪的影响,分析结果表明,温度和振动所引起的干扰主要集中于100Hz以下的低频成分中.为了消除这些干扰,设计了单臂补偿的反馈回路以稳定输出信号,并提出了一种利用象限判决方法来区分反馈正负性的动态补偿方法.实验中利用3×3耦合器3个输出端中其中2个进行光电变换、差分放大等反馈电路后驱动管状压电陶瓷,使缠绕在其上的光纤伸缩,动态补偿干涉仪相差的漂移,稳定干涉仪输出即3×3耦合器第三输出端口的信号.针对自然环境下温度和振动引起的干扰,本文研制了一种稳定的动态补偿装置,能有效抑制160Hz以下的低频干扰,实时补偿干涉仪两臂的相差漂移,干涉仪输出稳定的干涉信号,波动幅度小于5.64%.     

温度和振动对光纤马赫-曾德干涉仪的影响与动态补偿研究

环境温度变化和振动会引起光纤马赫-曾德干涉仪两臂相差随机性变化,致使干涉仪输出不稳定.本文研究了自然条件下外界温度和振动对基于3×3耦合器干涉仪的影响,分析结果表明,温度和振动所引起的干扰主要集中于100 Hz以下的低频成分中.为了消除这些干扰,设计了单臂补偿的反馈回路以稳定输出信号,并提出了一种利用象限判决方法来区分反馈正负性的动态补偿方法.实验中利用3×3耦合器3个输出端中其中2个进行光电变换、差分放大等反馈电路后驱动管状压电陶瓷,使缠绕在其上的光纤伸缩,动态补偿干涉仪相差的漂移,稳定干涉仪输出即3×3耦合器第三输出端口的信号.针对自然环境下温度和振动引起的干扰,本文研制了一种稳定的动态补偿装置,能有效抑制160 Hz以下的低频干扰,实时补偿干涉仪两臂的相差漂移,干涉仪输出稳定的干涉信号,波动幅度小于5.64%.     

起偏器参量对光学电流传感器性能的影响

以琼斯矩阵为数学工具,利用理论分析、计算机仿真和实验研究的方法,考察了偏振片的消光比和预偏角误差对光学电流传感器输出特性的影响.研究结果表明,上述偏振片参量均可在光学电流传感器的输出中引入直流分量,并使尺度因子发生一定的改变.当最终输出信号用交流电表度量时,输出信号中引入的直流分量可被交流电表中自带的隔直电容滤除,尺度因子的改变可用后续信号处理电路中的放大单元矫正.本研究结果可为光学电流传感器的设计人员提供有用的参考.     

相位调制激光多普勒频移测量方法的改进

本文对现有相位调制激光多普勒频移测量方法进行了改进,通过定义新的鉴频参量来同时利用相位调制信号直流和交流分量中的有用信息进行多普勒频移测量.由于相位调制信号直流分量中包含着调制信号光的Fabry-Perot干涉仪光强透过率,所以这一改进本质上是将基于Fabry-Perot干涉仪的边缘技术激光多普勒频移测量方法的优势引入到相位调制测量方法中,以提高其自身的性能.理论上证明改进后的相位调制激光多普勒频移测量方法无需对信号光的光强进行测量,所以可以进一步简化探测系统的结构和较少噪声混入的通道.另外,通过对改进前后鉴频和测量灵敏度曲线进行对比,还证明了其具有更高的测量灵敏度和动态范围.实验上对硬目标反射的频移可控信号光进行测量,不但证明了理论的正确性,而且证明了改进后的相位调制激光多普勒频移测量方法,测量动态范围提高约1倍,测量标准偏差降低约35%.     

激光超声位移场的共焦法布里-佩罗干涉仪检测技术

一般共焦法布里-佩罗(Fabry-Perot,FP)干涉仪只能检测声场的法向位移分量,而声场的切向位移分量含有法向位移分量所不能表达的材料特性。本文在检测声场法向位移分量共焦FP干涉仪的基础上,自行研制了一新颖的双通道共焦F-P干涉仪,它同时检测来自试样表面+θ和-θ角上的散射光,通过对两路输出信号作简单的信号处理,可以得到试样表面的位移点。用该F-P干涉仪测量了脉冲激光在Ti膜上激发的Lamb波的法向和切向位移,结果与理论预计一致。     

全光纤Mach-Zehnder干涉仪相位补偿的研究

阐述了一种由2×2耦合器和3×3耦合器构成的光纤Mach-Zehnder干涉仪(MZI),推导了干涉仪三个输出端光功率的表达式.由于光纤本身的特性,光纤构成的MZI容易受到外界环境的影响,针对这一问题,采用了一种平衡检测相位补偿方法.该方法是通过两个PIN分别对3×3耦合器两路光信号进行接收,并对两路光信号进行差动放大.实验表明该方法可以很好地消除外界环境对MZI干涉效果的影响.     

三分量全光纤加速度检波器及数字处理系统

研制出三分量全光纤加速度检波器及其数字信号处理系统。该检波器由一个质量块，六个顺变柱体，三组迈克耳孙干涉仪光路组成。顺变柱体是检波器敏感元件中的关键部件。该检波器数字信号处理系统以TI公司的高性能数字信号处理芯片为核心，辅以必要的电路，实现了对加速度信号的高精度检测和误差信号的补偿。测试结果表明，检波器在共振频率以上有较好的频率响应，输入信号与输出信号吻合较好；检波器在共振频率以下亦有较好的频率响应。最后给出了检波器频率响应曲线。     

干涉型光纤传感系统偏振分集接收实验研究

针对干涉型光纤传感器中存在的偏振诱导信号衰落现象,对偏振分集器(PDR)抗衰落原理进行了理论推导与软件仿真。设计并搭建了基于相位产生载波(PGC)调制解调、全光纤偏振分集器接收的光纤迈克耳孙型干涉传感实验系统,系统得出的信号与压电陶瓷光纤相位调制器产生的模拟信号基本相符。通过静态扭动干涉臂光纤改变干涉仪偏振状态,测量了PDR三通道可视度,得出信号稳定性、系统本底噪声与可视度的关系。结果表明,选择可视度大于0.5的偏振分集器通道输出可抑制信号衰落并实现信号稳定输出。     

基于3×3耦合器的迈克耳孙干涉仪相位特性分析

研究了基于3×3耦合器的非平衡迈克耳孙干涉仪的相位特性.由光纤耦合器的散射矩阵理论,推导出了当3×3耦合器分光比不均匀时,干涉仪三路输出信号相位差的表达式.根据实际使用的3×3耦合器各通道的插入损耗,经计算与修正得到其散射矩阵,并求出干涉仪三路输出信号的相位差分别为120.21°、120.77°和119.02°,与理想值120°的偏差在1°以内.实验测得的干涉仪三路输出信号的相位差随时间随机变化,经分析是由光偏振态随机变化引起的.相位差与理想值120°的偏离均在1°以内,符合理论分析得到的结论.     

Determining the phase-energy coupling coefficient in carrier-envelope phase measurements

For f-to-2f interferometers based on white-light generation in sapphire plates, the accuracy of the carrier-envelope (CE) phase measurement and stabilization is affected by the laser energy fluctuation. The coupling coefficient between the CE phase and the laser energy has been determined by modulating the pulse energy in an in-loop f-to-2f interferometer while measuring the CE phase variation with an out-loop interferometer. When the total spectral phase measured by the in-loop interferometer was locked, a 1% change in laser energy caused a 160 mrad shift in the CE phase of the output pulses.     

考虑到束-波相互作用的速调管离子噪声二维模拟

采用粒子模拟的方法并考虑电子束与电磁波的相互作用，首次直接得到了速调管输出信号的离子噪声图像，阐述了束电子、二次电子、离子、电磁场之间的相互作用的动力学过程. 指出离子噪声所表现出来的相位波动是由电子束速度的波动引起的，电子束速度的变化来源于管内离子数量的变化，离子的数量的变化又与电子束状态变化相互影响，这是离子噪声产生的根本原因. 二次电子对离子噪声产生过程的影响甚微，但是其行为却反映了离子噪声的形成机理. 离子噪声引发的输出信号幅度波动取决于电子束速度和半径的改变，与离子行为密切相关. 关键词： 离子噪声 速调管 粒子模拟 电子束     

Non-destructive observation of electrically detected magnetic resonance in bulk material using AC bias

DC bias is normally found in conventional measurements of electrically detected magnetic resonance (EDMR). Usually, electrodes are formed on the sample surface to make ohmic contacts for detecting changes in the electrical characteristics of the sample material. Thus, destructive procedures are required to detect the EDMR signal of bulk material with such methods. An AC bias detection technique was developed to allow the non-destructive EDMR measurement of bulk materials. An AC bridge circuit was constructed to detect the change in impedance of the sample, which when changed by ESR, an unbalanced AC voltage can be detected. By detecting this AC bias, it is possible to cancel the effects, such as Shottky barriers, that disturb the ohmic contact between the electrodes and a sample material. Further, the AC bias current penetrates the thin surface layer of a sample such as silicon oxide, which normally obstructs a DC current. This method was utilized using conductive rubber contacts for non-destructive EDMR measurements of part of a silicon wafer. EDMR spectra observed were the same as those obtained by the conventional method of using DC bias detection.     

Harmonic and Intermodulation Performance of Sagnac Fiber-Optic Interferometer

Abstract

In this article, closed-form expressions are obtained for the amplitudes of the harmonic and intermodulation products generated when driving the fiber-optic Sagnac interferometer by a DC bias voltage plus an equal-amplitude two-tone signal. The results clearly show the strong dependence of the harmonic and intermodulation performance on the DC bias voltage and/or the phase bias of the fiber-optic Sagnac interferometer. The results obtained suggest that the DC bias voltage and/or the phase bias play an important role in deciding the linearity of the fiber-optic Sagnac interferometer and, hence, its suitability for analog applications.     

星间微波光子链路调制方式的优化

针对外调制星间微波光子链路输出信噪比优化问题,建立了基于双电极马赫 曾德尔调制器的强度调制直接探测星间微波光子链路模型,通过优化调制器调制方式来提高链路性能。用数值模拟方法得到了单边带、双边带和推挽式3种调制方式下链路输出信噪比,利用曲面投影法求得了最优调制方式时一定信噪比要求下发射端所需最小光放大器增益和对应的调制器直流偏置相位。结果表明:相同输入射频信号功率和发射光功率情况下,双边带调制输出信噪比比单边带调制高3 dB,低直流偏置相位推挽调制可以进一步优化输出信噪比。输入射频信号功率为-20 dBm,输出信噪比为17.3 dB时,所需最小光放大器增益为43.9 dB,对应的直流偏置相位为0.87。     

Measurement of air refractive index based on surface plasmon resonance and phase detection

A method for refractive index of air measurement is presented based on surface plasmon resonance (SPR) and phase detection using a dual-frequency laser interferometer. Theoretical analyses indicate that the phase-difference variation of the measurement signal versus the reference signal is linear with refractive index of air (RIA) fluctuation, and the calculation formula of RIA is derived. The structure design of the self-adaptive SPR sensor greatly reduces the measurement error resulting from the incident angle shift and improves the sensitivity. The experiments show that measurement uncertainty of 10(-6) order has been achieved when phase detection precision is 0.1°. The phenomenon of sudden phase variation during air pumping and air filling, which is caused by temperature fluctuation, is discussed.     

Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer

A high powered Q-switched Nd:YAG laser was used to excite the surface waves, and an optical fiber sensor was used to detect the out-of-plane displacements due to the propagating waves. This sensor is based on the fiber optic Sagnac interferometer, which has the path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence in an optical path using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. The performance of the fiber optic Sagnac interferometer was investigated, and laser-generated surface wave signals were detected using this fiber optic sensor. The developed fiber optic sensor configured in this study is very simple and is effective for non-contact detection of ultrasonic waves.     

Analysis of fringe locking in a laser diode interferometer under injection-current modulation

A theoretical analysis has been performed that explains a fringe-locking phenomenon observed in a two-beam interferometer in which a laser diode was subjected to optical feedback and modulation of its injection current. The dependence of wavelength change on the injection-current variation is calculated by use of a model of coupled resonators consisting of the laser cavity and the interferometer. The fringe phase change caused by modulation of the injection current is derived from this model and has proved to be suppressed within much less than 2pi in excess of an integer multiple of 2pi if the path difference of the interferometer is longer than 10 mm. The calculated phase fluctuation agrees well with those observed in experiments.     

Feedback method of the noise suppression in wave-mixing amplifiers based on non-linear materials with photorefractive response in a reflection grating configuration

In the photorefractive wave-mixing system, fluctuation in the signal beam intensity of the photorefractive output with a reflection grating has been analyzed by employing pump feedback method. In this method, fluctuations of the photorefractive wave-mixing process not only induce the intensity fluctuation of the mixing waves but also induce phase fluctuation of the mixing waves. Thus, the phase of the pump and signal beams at the output surface fluctuates in time around a mean value. Using such a positive feedback method of a pump beams, the relative fluctuation in the photorefractive output signal beam intensity with respect to its mean intensity can be minimized significantly without reducing its mean intensity. The factors that control the fluctuation in the signal beam intensity, such as the phase fluctuation of the output pump beam, absorption strength of the material and the feedback reflectivity of the cavity mirrors, on the relative fluctuation of the output signal intensity in the photorefractive wave-mixing systems have been studied in detail. It has been found that the fluctuation of the output signal intensity relative to its mean intensity in the photorefractive wave-mixing system can be suppressed to larger extent by taking lower value of feedback reflectivity of the cavity mirrors which could exist at a higher value of absorption strength of the photorefractive materials.