Research And Design On The Micro-displacement Measuring System Of LD Self Mixing Interference

Laser self-mixing interferometry technology as a new measurement technique,having features of non-contact, high sensitivity and high precision, gradually play theadvantages in the field of precision optical measurement. With the development ofoptical technology, electronic technology and computer technology, the technology ofmicro-displacement measurement of laser self-mixing interference have obtained lots ofnew research findings. The LD as the light source of the system makes it have compactstructure,simple optical path and lower cost.The paper research the micro-displacementmeasurement system of the LD self-mixing interference under background, building andsimulatng the model of self-mixing interference mechanism, reserching the temperaturecontrol module of system to control the temperature precisely and reduce thetemperature error，completing the software and hardware design of the system in orderto achieve micro-displacement data processing and display.Firstly, analyse laser self-mixing interference technique theoretically based onthree-mirror F-P cavity equivalent mode, building and simulatng the model ofself-mixing interference mechanism in Matlab/Simulink. Obtain different signal ofoutput optical power in the level of weak, moderate and strong optical feedback. Thesystem of micro-displacement measurement design on the level of moderate opticalfeedback. Study the relation between output optical power signal and displacementsignal in moderate feedback level. Get the waveform of the signal of output opticalpower in the sine, triangle, and sawtooth wave displacement signal by simulating.Simulation results and theoretical analysis are virtually identical，so it can prove that themathematical model of mechanism of LD self-mixing interference is correct.Secondly, reserch the temperature control module of measurement system. LD isthe light source of the measuring system,and its change of temperature affects the resultof micro-displacement measuring, so this paper proposes Fuzzy-PID temperaturecontrol algorithm to control the temperature of the LD. Build the simulation model ofFuzzy-PID temperature control system in Matlab/Simulink, verifying the performanceof Fuzzy-PID controller by simulating. So the system can control the change oftemperature, and reduce the temperature error.Finally, design the hardware and software of the system, proposing overall systemarchitecture of the micro-displacement measurement of the LD self-mixing interference.The hardware circuit mainly includes LD modulation circuit, signal amplification andfiltering circuit, a differentiating circuit, AD converter circuit, and a USB to serialcircuit. Taking advantage of the high-frequency signal processing by FPGA, the systemhas designed FPGA module of data acquisition, date processing and serialcommunication, and simulate FPGA module by Quartus II software. Write PC programsof data processing and display using Visual Basic6.0software. Achieve FPGA and PCserial communication, micro-displacement data processing and the result display. Simulate the module of system, and the simulation results verify the feasibility andreliability of the system.