Research On The Self-mixing Laser Ranging Technology Based On Quadratic Feedback

The laser self-mixing interferometry technology is a new type of optical measurement technology formed by the coupling of external feedback light and laser emission light.Laser self-mixing interferometry technology has been widely used in different measurement fields such as displacement,distance and vibration due to its advantages of simple structure,easy alignment and low cost.With the development of aerospace and high-tech industries,the measurement of absolute distance has been receiving widespread attention.There is a practical need for measuring high-precision absolute distances.In a non-collimated laser cavity system,the beam returns after multiple feedbacks in the laser cavity.This phenomenon is called multiple self-mixing interferences.Compared with the traditional self-mixing interference,the resolution of the measurement system can be improved without increasing the complexity of the equipment.This project uses the advantages of high resolution,self-collimation,and low cost of MSMI to study the laser self-mixing ranging technology under multiple feedbacks,aiming to improve the self-mixing interference ranging.The main research contents of this paper include:Firstly,this paper analyzes the basic theory of self-mixing interference,and derives self-mixing interference theory from two aspects of the three-mirror cavity model and the Lang-Kobayashi rate equation theory.Obtaining the common power equation and frequency equation provides a theoretical basis for the study of self-mixing interference technology.Analyze the self-mixing interference model under different levels of optical feedback to lay the foundation for the simulation of self-mixing interference signals at different levels of optical feedback.At different levels of optical feedback,MATLAB was used to simulate the self-mixing interference waveform.Secondly,based on the principle of laser self-mixing ranging,different semiconductor laser frequency modulation principles and different types of continuous wave modulated semiconductor lasers are analyzed.This lays a theoretical foundation for studying the current modulation of laser diodes with different waveforms.Then,aiming at the problem that the traditional self-mixing interference distance measurement accuracy is low precision,this paper studies the self-mixing interference theory of multiple feedbacks.Based on the multiple self-mixing interference theory,the current modulation of the laser tube is established using triangular wave signals.A distance measurement model of triangle wave current modulation laser self-mixing interference based on secondary feedback was established.Through the theoretical analysis,the distance measurement formula was deduced.Based on the theory,a simulation experiment of the self-mixing interference distance measurement of triangular wave current modulation laser based on one feedback and two feedbacks was performed.An experimental platform was built to verify the correctness of the triangle-wave current modulation laser self-mixing interference distance measurement model based on the secondary feedback.This method doubles the accuracy of the self-mixing interference distance measurement of the current-modulated laser compared to a feedback.Finally,in order to improve the accuracy of the self-mixing interference distance measurement based on the secondary feedback,the phase modulation method is studied in this paper.The sine wave signal is used to current modulate the laser diode,and the double sine based on the secondary feedback is analyzed.The FFT method is used to analyze the self-mixing signal and obtain distance information.Compared with the secondary feedback current-modulated laser self-mixing interferometry method,this method increases the complexity of the experimental device,but it can achieve higher measurement accuracy.