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.     

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。     

Self-mixing effect in Yb3+ doped DBR fiber laser with different linewidth enhancement factor

We present a self-mixing interference model approach to stimulate the self-mixing interference in YDBR fiber laser with optical self-mixing interference operating in the weak feedback regime. The self-mixing interference model includes Yb³⁺ doped fibers pumped at 920 nm, with distributed Bragg reflector mirrors at both fiber ends and external reflector. Using the quasi-analytical YDBR fiber laser model and self-mixing three-mirror cavity model, the output power expression is deduced and the Peak-to-Peak values and asymmetry values of self-mixing waveform at different linewidth enhancement factor have been studied in detail.     

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。     

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。     

仿真分析测量参数对光反馈自混合信号的影响

针对含有光反馈的半导体激光器,在外腔波动条件下,研究其光反馈干涉自混合信号模型。经计算仿真分析,得到了外腔运动参数及激光器本身参数的变化对光反馈自混合信号波形的影响规律。结果表明,利用光反馈自混合干涉效应可以进行多参数传感测量。     

Fourier transform method for self-mixing interference signal analysis

Self-mixing interferometry (SMI) has been used to measure the distance and displacement. Although the principle of self-mixing interference is different conventional interference, we concluded that FFT analysis technique could also be used to detect the signal phase and increase the measurement precision of self-mixing interferometry.First the SMI signal is obtained by feeding the light from the target to cavity of laser diode, then it is pre-processed by an analog subtraction circuit to remove the overlapped output intensity due to the injection current modulation. Finally, SMI signal is analyzed by FFT phase detection method. Theoretical analysis and simulation calculations are presented. Experimentally, displacement of a PZT-driven target was measured with a precision of λ/50.     

The simulation of self-mixing interference effects in three-section DBR lasers

The self-mixing interference in three-section distributed Bragg reflector (DBR) lasers is analyzed based on the model of F-P cavity and coupling wave equation. The oscillating frequency and threshold variation are deduced. The influence of internal and external parameters on the output intensity and the inclination degree of waveform are discussed in simulation.     

激光二极管自混合干涉的计算分析和实验观察

实验上观察到自混合干涉信号的幅度仅仅为静态光强的百分之几.反馈光会引起激光二极管阈值电流减小,静态输出光强变化几倍,使激光二极管工作在实际的阈值电流之上.按三镜法布里-珀罗腔结构模型计算激光二极管的出射光强,由干涉函数主极大条件得出光频与反馈光的关系.计算出的自混合干涉信号的波形,以及自混合干涉信号的幅度与静态光强的比值均同实验测量结果一致.在τrC/τ1=22.8的情况下,复合谐振腔可同时有15个谐振模式,这些模随外腔长度的变化小于2.6×10-2cm-1,远小于法布里-珀罗谐振腔谐振模的线宽3.1cm-1,光频在内腔谐振模的线宽以内变化.     

Self-mixing interference effect of DFB semiconductor lasers

This paper analyzes the self-mixing interference in DFB (distributed feedback) semiconductor lasers. The general expression of the threshold gain and frequency in the DFB lasers was deduced. Numerical simulations indicate that, for specific coupling coefficient and cavity length value, the DFB lasers are more sensitive to optical feedback than the Fabry–Perot semiconductor laser. These results show that high-accuracy self-mixing sensors can be obtained by using the DFB lasers. PACS 42.55.Px; 42.60.Lh; 42.87.Bg     

Numerical simulation of phase modulation method used as high sensitive self-mixing vibrometry in vertical-cavity surface-emitting laser

The self-mixing interference technique is a compact sensing technique that has widely used for measuring vibrations. For purpose of increasing the accuracy of the vibration measurement system, a new phase modulation technique based on the self-mixing interferometer is presented. The phase modulation is obtained by varying the length of external cavity periodically. The vibration information of the external target is determined by the Fourier analysis method. Theoretical analysis and numerical simulations of phase modulation method used as high sensitive self-mixing vibrometry based on vertical-cavity surface-emitting laser are given in this paper.     

Laser self-mixing interference fibre sensor

Fibre sensors exhibit a number of advantages over other sensors such as high sensitivity, electric insulation, corrosion resistance, interference rejection and so on. And laser self-mixing interference can accurately detect the phase difference of feedback light. In this paper, a novel laser self-mixing interference fibre sensor that combines the advantages of fibre sensors with those of laser self-mixing interference is presented. Experimental configurations are set up to study the relationship between laser power output and phase of laser feedback light when the fibre trembles or when the fibre is stretched or pressed. The theoretical analysis of pressure sensors based on laser self-mixing interference is indicated to accord with the experimental results.     

自混合干涉信号的位相调制

自混合干涉因其结构简单、紧凑、稳定且易准直等特点而被广泛应用于测量领域。从自混合干涉和电光晶体调制位相的基本原理出发,通过将电光晶体引入自混合干涉外腔调制,研究了自混合干涉测量中电光晶体的位相调制性能。实验证明,利用晶体的调制性能对自混合干涉信号进行位相调制,在很宽的频率范围内都能保证很高的调制精度,测量误差小,具有很好的应用前景。     

Influence of external objects scattering property on self-mixing signal inside fiber laser

The self-mixing sensor based on Er³⁺–Yb³⁺ co-doped Distributed Bragg reflector fiber laser (EYDBR) has been demonstrated for detecting the effect of external objects scattering property on self-mixing signal. Results show that self-mixing interference inside fiber laser with short cavity length especially EYDBR fiber laser can keep high SNR with different types of scattering surfaces even the white print paper. Meanwhile, we have obtained a high and stable SNR at least 29.9 dB in measurements at incident angles smaller than 20°. In this way, the sensing system we demonstrate is suitable for vibration and displacement measurements, particularly for high-precision industrial measurements.     

Nanometer-scale displacement sensing using self-mixing interferometry with a correlation-based signal processing technique

A self-mixing interferometer is proposed to measure nanometre-scale optical path length changes in the interferometer’s external cavity. As light source, the developed technique uses a blue emitting GaN laser diode. An external reflector, a silicon mirror, driven by a piezo nanopositioner is used to produce an interference signal which is detected with the monitor photodiode of the laser diode. Changing the optical path length of the external cavity introduces a phase difference to the interference signal. This phase difference is detected using a signal processing algorithm based on Pearson’s correlation coefficient and cubic spline interpolation techniques. The results show that the average deviation between the measured and actual displacements of the silicon mirror is 3.1 nm in the 0–110 nm displacement range. Moreover, the measured displacements follow linearly the actual displacement of the silicon mirror. Finally, the paper considers the effects produced by the temperature and current stability of the laser diode as well as dispersion effects in the external cavity of the interferometer. These reduce the sensor’s measurement accuracy especially in long-term measurements.     

Research on micro-vibration measurement by a laser diode self-mixing interferometer

The self-mixing vibration signals are observed in the laser diode when the optical beam is back-scattered into the laser cavity which causes laser output power modulated. Based on these properties, a laser diode self-mixing vibrometer with wide dynamic range is proposed. This current investigation further reports new work to improve the accuracy and range of the measured vibration signals. Numerical simulations and experimental results are given and discussed. The experimental results show that the frequency measurement range can be achieved up to 22 kHz with 0.241% maximum relative error while utilizing the reflecting film. For amplitude measurement utilizing the same reflecting film, the error of measurement result is 4.77 nm which has approached nanometer order of magnitude.     

Self-mixing interference effects in orthogonally polarized dual-frequency Nd:YAG lasers at different feedback levels

The self-mixing interference effects are investigated in birefringence dual-frequency Nd:YAG lasers at different optical feedback levels. For weak feedback level, both of the intensities of the two modes are sinusoidally modulated by external cavity length with a feedback period of half laser wavelength. While these two modes can only coexist in a part of feedback period at moderate feedback level, i.e., one mode reaches its maximum intensity, the other one extinguishes. At high feedback level, complete polarization switching (one mode oscillating, the other one extinguishing) between two polarized modes is observed, and every switching corresponds to quarter-wavelength variation of external cavity length. Furthermore, two feedback schemes, i.e., isotropic optical feedback (IOF) and polarized optical feedback (POF) are taken into account. The theoretical analysis based on a model of two-mode-coupled laser is presented, which is in good agreement with experimental results. Our results can advance the research of self-mixing interferometer of orthogonally polarized dual-frequency lasers.     

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 discovery of nanometer fringes in laser self-mixing interference

We demonstrate the influences of optical feedback from an external mirror with high reflectivity in a He-Ne laser on self-mixing interference fringes and laser polarization states. When the external mirror is tilted to a certain level, the stable and uniform nanometer resolution fringes are generated. The fringe density is 40 times than that of the conventional self-mixing interference or two beam interference, and has still potential to be improved. Each self-mixing interference fringe corresponds to λ/80 displacement of the external mirror, i.e. 7.91 nm displacement of the external mirror. Moreover, when the movement direction of the external mirror is changed, the polarization flipping between two eigenstates will happen. The potential applications of the results are also discussed.