Research On FPGA Signal Processing In Laser Self-mixing Interferometry System

Along with the theory research of the laser self-mixing interference becoming more mature increasingly,this technology is applied in distance,micro-displacement,velocity measurement,and so on.Laser self-mixing interference technology in the laser application system refers to the laser light reflected from the object,feedback to the laser cavity,and the cavity of optical coherence,causing the laser output power changes.We could complete the relevant measurement technology by detecting the power fluctuation signal.However,this technique is still much left for improvement in the industrial applications,such as the higher accuracy of the technology,the faster digital signal processing,the smaller volume,the lower prices and the better human-computer interaction.Based on the characteristics of the laser self-mixing interference technology,we introduce the FPGA(Field-Programmable Gate Array)technology into this measurement system.We study the digital signal process using the FPGA in the micro scale measurement system.This paper introduces the principle of sine wave phase modulation and triangular wave frequency modulation in the laser self-mixing interference measurement system.We adopt the FPGA-DDS principle to design a signal source to generate the modulation signals and text signals which have been used in the measuring experiments.We focus on the analysis of the demodulation technology of two kinds of modulation methods.The pre-processing analog circuit has been designed.The scheme of human-computer interaction and the communication protocol between FPGA and MCU have also been studied.In this measurement system,only one chip is used to implement the feature of the modulation signal source module and signal processing module.The size and cost of the system is reduced.It is demonstrated/proved by experiments that the FPGA module can achieve a good multiplier effect of different needs.Due to the self-mixing system has small volume,simple structure,easy to implement,the system has the advantage that combines self-mixing and FPGA which has high integration,high computing speed.And that will make the measuring instrument towards miniaturization,intelligent,portable.So the technique would be used more widely.