Displacement measurement method based on laser self-mixing interference in the presence of speckle

In order to achieve the accurate measurement of displacement, this Letter presents a self-mixing interference displacement measurement method suitable for the speckle effect. Because of the speckle effect, the amplitude of the self-mixing interference signal fluctuates greatly, which will affect the measurement accuracy of displacement. The ensemble empirical mode decomposition is used to process the interference signal, which can filter out high-frequency noise and low-frequency noise at the same time. The envelope of the self-mixing interference signal is extracted by Hilbert transform, and it is used to realize the normalization of the signal. Through a series of signal processing, the influence of speckle can be effectively reduced, and the self-mixing interference signal can be transformed into standard form. The displacement can be reconstructed by fringe counting and the interpolation method. The experimental results show that the method is successfully applied to the displacement measurement in the presence of speckle, which verifies the effectiveness and feasibility of the method.     

光纤耦合自混合干涉测速系统的参数研究

针对光纤耦合自混合干涉测速系统的设计,采用F-P五镜腔模型分析了自混合干涉测速的基本原理,利用数值计算软件MATLAB研究了系统中各个参数对自混合信号波形的影响。对参数引起自混合信号波形“畸变”的情况,进行了参数的优化设计。为光纤耦合自混合测速系统设计,以及将其应用于爆轰波和冲击波研究中进行高速测量提供了参考。     

基于DSP的激光自混合干涉测振仪信号采集与处理系统

结合三角波电流调制型激光自混合干涉技术,设计了基于DSP的数据采集与处理系统,完成了对来自光电探测器的干涉信号的采集与处理。该系统接口电路简单灵活,具有采样频率可由程序设置、采集速度和精度较高,并且可以实现6通道同步采样转换的特点。实验结果表明,该数据采集与处理系统完全能够满足高速交变激光自混合干涉信号的采集与处理在实时性和高精度方面的要求。     

基于光反馈自混合干涉效应波形转折点的智能识别

对光反馈自混合干涉信号波形转折点的智能识别进行了理论分析和实验研究。首先经对光反馈自混合干涉信号特点的分析，发现其波形转折点可以作为外部物体运动位移实时测量的依据。通过对信号波形的逐步处理可以获得波形转折点的位置，以此为基准点可以实现位移的精测。实验测试结果同理论分析吻合较好。若系统进入较复杂状态，识别出的位置与其实际位置出现偏差，不再是单一值，可以对转折点位置的所有值取平均，从而得到其对应的精确位置。     

Effect of angle of incidence on self-mixing laser Doppler velocimeter and optimization of the system

Based on the theory of speckle and self-mixing interference in laser-diode, three-facet cavity model is introduced to analyze laser Doppler effect based on self-mixing interference in the case of a rough surface, and numerical solution of the signal is obtained. Simulation results of speckle-modulated Doppler signal based on self-mixing effect and tracking accuracy at different incident angles are given using parameters employed in the experiment. Simulation results indicate incident angle of around 30° is most suitable when both tracking accuracy and signal amplitude are considered. Experimental waveforms agree well with simulation results, and similar conclusions as simulation predictions about changing trend of tracking accuracies of the system at different incident angles can be made. Combining with difference frequency analog phase-lock loop (PLL) technique and appropriate sampling time, a laser Doppler velocimeter with tracking accuracy better than 1.3% in the range of 10-470 mm/s is realized.     

半导体激光器的自混合散斑干涉测量流体速度

提出了一种简便的激光自混合散斑干涉测量流体速度的方法。根据散斑和法布里-珀罗腔的理论,提出了半导体激光器的自混合散斑干涉模型。研究了流体运动时在半导体激光器内产生的自混合散斑干涉效应(SMPI),给出了激光器输出增益的变化及其概率密度分布。得到了激光自混合散斑干涉平均频率与流体速度之间的关系。模拟计算和实验结果验证了这个关系。利用散斑干涉的平均频率与流体速度的关系测量了高分子材料溶液的速度,并在溶液浓度和背景光变化时,对流体速度进行了测量、比较和分析。实验表明。在溶液浓度不太低时,测量误差小于8％。     

Autocorrelation of self-mixing speckle in an EDFR laser and velocity measurement

Autocorrelation analysis for a velocity measurement based self-mixing speckle in an erbium-doped fiber ring (EDFR) laser is presented. The expression for the velocity measurement is deduced. Theoretical analysis reveals that the velocity of a random surface is inversely proportional to the autocorrelation time of the self-mixing signal produced in the EDFR laser. In experiments, a linear fit between the velocity and the reciprocal of autocorrelation time (autocorrelation frequency) is obtained for velocity measurement. In a range of velocities from 100 mm/s to 350 mm/s, the measurement errors are evaluated to be less than 5%. The signal length, the measurement distance, and the pump power are experimentally studied for gaining knowledge of the influence on the velocity measurement.     

Measurement of the velocity inside an all-fiber DBR laser by self-mixing technique

The self-mixing interference for optical velocity sensing is experimentally investigated in an all-fiber configuration distributed Bragg reflector laser. Simultaneously, theory model of self-mixing interference laser Doppler velocimeter based on quasi-analytical method. The experimental results show Doppler shift frequency is linearly proportional to the value of the velocity which agrees well with theory analysis. The results preserve an enough signal-to-noise ratio around 40 dB in the range from 39.3–317.0 mm/s (measurement range depending on bandwidth of circuit) for velocity measurement. Additionally, the cutoff circuit is used in our system to get a stable Doppler signal and reduces the error rate to 0.136 % in practical measurement.     

半导体激光自混频干涉速度仪的F-P模型分析

设计了一个半导体激光自混频干涉式测量物体振动速度的实验,利用双镜F_P(法布里_珀罗)等效模型,对半导体激光自混频干涉速度仪中的干涉效应进行了理论分析,推导了干涉信号理论模型的数学表达式,讨论了影响测量信号的因素。结果表明,在半导体激光自混频干涉速度仪的无源腔中空气密度的变化、无源腔长度的变化、激光波长的变化都将会导致信号漂移,从而引起测量误差。而被测物体表面的反射率越高,越有利于测量。     

The study of laser self-mixing vibrometer employing different feedback regime using a VCSELS

Laser interferometry based on self-mixing effect widely used to measure displacement, velocity, vibration and distance due to compactness, non-contact, as well as low cost. An important use of the self-mixing effect inside a laser diode is in optical self-mixing vibrometer. We have experimentally investigated self-mixing interference produced by the feedback of light from a vibrated target into a vertical-cavity surface-emitting laser for sensing applications. In this paper, the self-mixing vibrometer employing different feedback regime is discussed and a theoretical analysis is also proposed. Numerical analysis focused on the distortion self-mixing waveform. Numerical analysis and experimental results show that mode-hop occurs when the laser self-mixing vibrometer employing at high feedback level.     

大气颗粒物多参数激光自混合传感的数值模拟与特性分析

基于颗粒物米氏散射特性、激光自混合三镜腔理论和激光器稳态条件,推导出在大气颗粒物光反馈下激光器频率、功率、线宽的理论表达式,建立了大气颗粒物光反馈下的激光自混合理论模型。同时,数值模拟和分析了大气颗粒物物理参数对激光自混合干涉信号的影响。结果表明,在一定粒径范围内,激光自混合反馈强度随大气颗粒物粒径增大先增大后减小,且反馈强度峰值出现的位置随颗粒物折射率实部的增大、虚部的减小向粒径较大处移动;自混合系统的外腔长度影响自混合干涉信号的波动深度,激光器输出光信号的幅值随外腔长度增大呈指数衰减;自混合干涉信号波动频率与大气颗粒物运动速度呈线性关系。分析结果对基于激光自混合效应的大气颗粒物多物理参数传感具有重要作用。     

利用自混合干涉效应的条纹计数法对扬声器振动特性的实验研究(英文)

基于半导体激光器的自混合干涉效应，通过实验研究了扬声器的振动特性。实验中，用粘在扬声器振膜上的反射镜作为目标物体（该反射镜的反射率为95％，扬声器用50Hz的正弦波驱动）,然后通过条纹计数法获得扬声器的振幅。实验结果表明，在一定范围内，扬声器的振幅与驱动电压呈线性关系。该实验装置极其简单紧凑，自混合干涉信号也十分清晰，实验方法迅速，价格低廉，易实现，而且不需要专用电源，也不需要其他的光学仪器，这一系列优点充分表明自混合干涉技术在振动测量领域具有广阔的发展前景。     

Quadrature demodulation technique for self-mixing interferometry displacement sensor

A new, to the best of our knowledge, signal processing method based on quadrature demodulation technique is presented for laser diode self-mixing interferometry(LDSMI) displacement sensor. Phase modulation of the laser beam is obtained by an electro-optic modulator (EOM) in the external cavity. Detection of the target's displacement can be easily achieved by sampling the interference signal at those times which satisfied certain conditions. The major advantage of the technique is that it does not involve any complicated calculation and insensitive to the sampling error. Experimental results show that the proposed method can effectively improve the displacement measurement resolution of the laser diode self-mixing displacement sensor to a few nanometers.     

激光自混合干涉测振仪的硬件系统设计

基于激光自混合干涉技术的特点,设计了一种新型半导体激光自混合干涉测振仪系统。系统将频率调制引入自混合干涉中,实现对振动物体的非接触式测量。介绍了激光自混合干涉测振仪的原理、仪器系统的光路系统设计、信号的调制模块设计、解调模块设计以及DSP系统的采集处理模块设计。该仪器体积小、成本低、易于准直、可以非接触式测量,能够测量振动频率在50kHz内的物体,其中包括非周期性振动。可以测量出振动物体的振动频率、振幅以及还原振动波形,振动幅度测量精度可以达到0．325μm,频率精度为1Hz。     

激光二极管自混合干涉信号随外腔长度衰减

理论分析了激光二极管自混合干涉信号随外腔长度增大的变化特点及规律。从复合谐振腔干涉函数出发,推导出激光二极管自混合干涉信号随外腔长度增加指数衰减,衰减系数与光频虚部成正比,并给出光频虚部和实部满足的超越方程组。求解该超越方程组得到,当外腔长度超过一个临界值时,光频虚部随外腔长度近似反比衰减,则激光二极管自混合干涉信号随外腔长度增加衰减很缓慢;当外腔长度小于该临界值时,外腔反馈会使光频虚部增大,而且光频虚部随外腔长度变化而振荡,激光二极管自混合干涉信号出现复杂的状态。外腔反馈强度越大,或激光单模线宽越大,这一外腔长度的临界值则越小。分析激光二极管自混合干涉还需要考虑外腔反馈对光频虚部的影响。     

Effect of speckle pattern on laser Doppler velocimeters

The effect of speckle pattern on laser Doppler velocimeters is studied theoretically and experimentally. We have found that dynamic speckle patterns can cause error in velocity measurement. Increasing sampling time and using proper signal processing circuits can eliminate this bad effect caused by speckle pattern.The accuracy of velocity measurement is better than 2.1％ in a wide velocity range(4.66-468.86 mm/s)when speckle effects are taken into account.     

光纤激光器自混合干涉效应研究

针对光纤激光器自混合干涉传感应用,研究了光纤激光器自混合干涉特性,运用四镜法布里-珀罗腔模型对掺铒线形腔光纤激光器自混合干涉效应进行了理论分析,对不同反馈水平下的自混合干涉信号进行了数值模拟,获得了光反馈条件下光纤激光器输出特性.外腔长度的改变会调制激光器的输出强度,外腔长度变化半个波长,对应一个干涉条纹,弱反馈条件下,由反馈引起的激光器的频率变化可以忽略.设计了基于光纤激光器的自混合干涉实验,实验结果和理论分析相符合.此研究结果为进一步开展光纤激光器的自混合干涉传感应用研究奠定了理论与实验基础.     

半导体激光自混频干涉法测振动速度

应用半导体激光自混频干涉方法可研究物体的振动速度．本文阐述了测速的基本原理，给出了信号分析的理论依据和计算方法。     

激光自混合显微系统的设计及实验研究

论述了自混合干涉技术的发展历程,并引入了自混合干涉显微技术的实验原理和研究近展;建立了He—Ne激光自混合干涉实验装置系统,获得了稳定的激光功率输出。然后,对基于激光自混合干涉技术的显微镜进行了研究,并详细给出了该系统的设计原理、装调方法和实验结果,得到了玻璃小球的三维形体信息图像。系统达到的横向分辨力1μm,纵向分辨力为15nm。上述实验结果证明自混合显微镜在微小物体的高精度形貌成像方面有着很大的潜力。     

半导体激光器内自混合散斑干涉

在散斑和半导体激光器的自混合干涉理论的基础上,提出了基于法布里一珀罗腔的自混合散斑干涉模型,对粗糙表面产生的激光器内自混合散斑干涉效应(SMSI)进行了详细的理论研究和分析,得到了粗糙腔条件下的激光动力学的数值解。模拟产生了高斯相关随机表面及其在夫琅禾费面上产生的散斑场,以及该散斑场与相干光场叠加所形成的光场,分析了这些情况中光强的统计特征,与已知实验情况进行了对比,模拟结果与已知统计结果相同。给出了粗糙表面运动时激光器输出增益的变化及其概率密度分布。对由于照明宽度和外腔长度的变化而给粗糙表面运动时激光器输出增益变化带来的影响进行了分析。实验结果和模拟结果相符。