Design Of Laser Self-Mixing Interference Displacement Measuring System

The Self-mixing Interference (SMI) effect occurs when the light emitted from the laser is reflected or scattered from the external target, a portion of the laser output which contains the information of the target back into the laser cavity and mix with the original light in the laser cavity, resulting in the change of the output power. The SMI technique has been widely used in the measurements of semiconductor laser parameters, geometric and mechanical quantities for its significant advantages in simplicity, compactness and self-aligning. The displacement measurement which is applied in measuring is an important aspect.This thesis mainly studies the displacement measurement which is based on the laser self-mixing interferometry effect. The fringe counting method is used to achieve the displacement measurement. And using system generator development tool the displacement measurement system is accomplished in the Matlab/Simulink environment. The proposed methods are tested and verified by both simulations and experiments. The main tasks are as follows:First of all, the paper describes the theory of self-mixing interference displacement measurement technique and its research status. The methods of displacement measurement based on self-mixing interference are introduced. And the principle of fringe counting is also introduced. By studying the basic theoretical model of SMI effect, the influence of the system parameter on the SMI signal waveform is discussed and studied in the paper. According to the theoretical study, displacement measurement algorithm is designed.Secondly, using the system generator development tool that is provided by Xilinx, the FPGA design of displacement measurement algorithm is completed in Matlab/Simulink environment. By comparing the results of the Simulink software simulation and hardware co-simulation, the correctness of the hardware co-simulation and hardware feasibility is verified.Thirdly, the Xilinx's Spartan-3E Starter Kit Board is chosen as a hardware platform. And the displacement measurement system is built in the laboratory. To improving the accuracy of measurement, the experimental data is filtered. And then the preprocessing data is tested. According to analyzing the results of measurement, the stability and effectiveness of the measurement system was verified. And the experimental results also show that the absolute error is less than half the laser wavelength.At last, conclusions are drawn from the whole paper and the further research issues are pointed out.