A Study On Absolute Distance Measurement Based On Laser Self-mixing Interference

Laser self-mixing interference refers to emitting light of lightemitting diode in laser is reflected or scattered by the external target object, some light which carries target object information reflected back into the laser cavity resonator, and mixed with the laser in cavity,thereby causing the phenomenon of laser light photodiode output optical frequency and powerchange. The semiconductor laser interference measurement technique is an emerginglaser measurement technology, the measurement system is simple, and it is only composed of laser, detector, the target object and a signal processing circuit. The system not only has a non-contact, high-precision, strong anti-interference, fast response characteristics,but also possesses compact structure, easy alignmentadvantages, therefore more and more attention has been paid to research scholars, and widely used to measure absolute distance,displacement, vibration sensing and other areas.This paper introduced the basic theory of self-mixing interference technique, summarized its research and application progress, through the L-K rate equation theory and three mirror cavity(F-P) derivation to establish a general model of laser self-mixing interference. Different self-mixing interference of optical feedback are analyzed and the simulation waveform is carried out.Based on the basic theory of self-mixing interference, the paper described the principle of laser self-mixing interference ranging, introduced the classification of laser ranging technology and presented three different ranging methods in accordance with the principles,designed laser self-mixing ranging experiment system by selecting the best ranging method.According to the experimental results, the factors that affect the accuracy of the measurement are analyzed and the accuracy of the measurement system is further improved by optimizing the parameters.On this basis, this paper proposes a scheme to improve the range accuracy, which adopts analog phase-locked loop to process the collected laser self-mixing signal, to further improve the self-mixing waveform phase discontinuity to make self-mixing wave more regular.Through the experiment simulation and error comparison, it is founds that the precision of laser self mixing interference measurement is greatly improved after using phase-locked loop technique, verifying the feasibility of the improved scheme.