Signal Processing Circuit Design Of Self-mixing Interference Displacement Measurement System

Laser self-mixing interference (SMI) effect refers to that in laser application system, light outputted by laser conducts feedback to internal resonant cavity after external object reflection or scattering. After mixing with internal light of the cavity, feedback light will regulate outputted light, thus changes energy as well as frequency of the outgoing laser. Feedback light can be employed for geometrical and semiconductor laser parameters measurement with the reason that it carries parameter information of external reflected objects and semiconductor laser. So, laser self-mixing interference can be used for the measurement of geometric parameters, mechanical parameters and semiconductor laser parameters.Based on the theory of stripe counting model, this paper gives a new program about displacement measurement. The program is composed with A/D converter module, the signal processing module and LCD display module. Then to get the displacement the Real-time processing of the self-mixing interference signal is completed by designing the various parts. The details are listed below.Firstly, we introduce the home and abroad development of Laser self-mixing interference technique and the method of measuring displacement. After researching the stripes counting theoretical model, the integrated design of displacement measurement is built on the theory. The design is composed with A/D converter module, the signal processing module and LCD display module.Secondly, we can use the system generator development tools to design the digital signal processing module design in the Matlab/Simulink environment, and complete the simulation of the verify the correctness of the program design; the assembler the Picoblaze microprocessor, A/D conversion and LCD display the module function; using VHDL top-level file to the A/D converter module, LCD display module and data processing module function jointly to complete the real-time processing and display of the self-mixing interference signal.Lastly, the entire design is downloaded to development board through synthesize, implement, generate programming file and configure target device in ISE development environment. The development board is real-time detected by ChipscopPro Tools through the design of the hardware test program to verify the correctness of the data transfer.