Research On Absolute Distance Measurement Based On Self-mixing Interferometry

In order to measure absolute distance for micro-device in a narrow space,a method of absolute distance measurement based on self-mixing interferometry was proposed.This method has not only the advantage of traditional optical distance measurement such as high-precision,high efficiency,no damage for object but also its simplicity,compactness,and low demand for reflecting surface,which is fit for distance measurement in narrow space.This thesis carried out research on self-mixing interferometry based on vertical-cavity surface-emitting laser(VCSEL)for absolute distance estimation.First of all,the power and frequency function of self-mixing interferometry based on three-facet Fabry–Perot cavity and rate equation were deduced and self-mixing interferometry was simulated,and then theories of distance measurement through self-mixing interferometry was proposed,that is,distance measurement can be carried out by calculating the frequency of power function or by analyzing the power function with intelligent algorithm.Secondly,experimental setup for distance measurement was established on the basis of theory analysis.The setup is constituted by optical part and electrical part.The parameters of optical part were presented.The designing scheme of drive circuit for laser and preprocessing circuit were established and selection of component was discussed.Finally,emulational and experimental results were presented after the process of self-mixing signal by all phase fast Fourier transformation(all phase FFT)and particle swarm optimization(PSO)algorithm.All phase FFT was utilized in order to diminish spectrum leakage,while PSO was used to avoid spectral analysis for the purpose of eliminating spectrum leakage.The analysis and the improvement of phase difference correction method were discussed in this thesis and a phase difference correction method based on wrapping was proposed.The results of numerical simulation show that the improvement of correction method is effective and all phase FFT can achieve a higher frequency precision than FFT.As to PSO algorithm,selection of inertia weight was discussed to make a tradeoff between the global and local search.In addition,we implemented a way to shrink the exploration range before the implement of PSO to accelerate the speed of measurement in order to decrease the time consumed.The experimental results show that all phase FFT can achieve a resolution of 50 ?m in the range from 30 to 50 mm and PSO algorithm can achieve a resolution of 30 ?m in the same range.However,time consumed of PSO algorithm is 20 times that of the all phase FFT,that is,the PSO algorithm has higher precision at the price of sacrifice of real time measurement.