Simulation And Experimental Study Of Displacement Measurement Based On Self-mixing Interference

The problem of self-mixing interference stems from the optical feedback effect. Initially, people always tried to eliminate the optical feedback effect, but gradually people began to make use of it actively to measure all kinds of physical quantities. So the technology based on self-mixing interference was brought forth. In recent years, this kind of technology has been increasingly of interest because of simplicity, compactness and easy alignment. It's a solution to the problems of complexity, large size and sensitive alignment that are typical of all conventional interferometers. This thesis has studied the principle of self-mixing interference and the displacement measurement. The principal work is as follows:(1) The principle of self-mixing interference effect is studied. Laser system's stable condition and frequency function are gained by virtue of theoretical model of a three-mirror F-P cavity and semiconductor laser, and then the mathematical model of common self-mixing interference effect is established. Especially under the condition of micro displacements of reflector, the mathematical model of displacement measurement is established. Results show that the displacement sensor based on self-mixing interference has the same phase sensitivity as a conventional interferometer.(2) The properties of displacement measurement based on self-mixing interference are mathematically analyzed. First, how the external phase influences upon the output frequency, intensity, power and line-width is discussed. Then, the output signal's properties modulated by four waves, including sine wave, square wave, triangular wave and saw tooth wave, is discussed.(3) The shape of signal fringe is discussed. First, how the feedback level influences upon the shape of signal fringe is studied. And find out the reasons of fringe's inclination and waveform's inversion. The conditions of stability when the multi-mode laser system is usedare discussed.(4) The self-mixing interference effects are observed in experiments. Using booster and signal generator to modulate PZT, the experimental results are coherent with theoretical conclusions. Analyze the reasons of the error between the measured displacements and the given values.(5) Programs to analyze the results of displacement measurement based on self-mixing interference effect are presented by use of Matlab and Delphi.