Study On Laser Doppler Velocimeter By Self-mixing Effect In Single-mode VCSEL

The works in this thesis are on the basis of international cooperate projects.The project on single mode vertical-cavity surface-emitting laser(VCSEL)laser Doppler velocimeter(LDV)has been complete successfully.We have emphasized the study of measurement precision,dynamic range and direction discrimination of LDV system.The main research works and conclusions are as following:(1)Cooperate with project members in completing the theory and system researches of single mode VCSEL LDV.We have constructed single mode VCSEL LDV experimental setup and designed optoelectronic signal processing circuits of LDV system,then we have analyzed main factors influencing the system important parameters in theory and experiment,such as velocity measurement precision, dynamic range and direction discrimination precision,etc.A LDV tracking prototype has been developed and a patent on LDV senser is obtained.(2)We use single mode VCSEL in place of common semiconductor Laser diode(LD),and the dynamic range of external cavity length of LDV system has been expanded obviously,and velocity measurement precision has been improved.We use difference frequency analog phase-locked loop(PLL)technique to process Doppler signal,and the velocity measurement error induced by Doppler signal spectrum width and amplitude modulation(AM)envelope has been reduced.The measurement precision has been reached 1%,and the tracking frequency range has been expanded, so that the velocity measurement range is 5～500mm/s.(3)We use triangular wave current modulating the VCSEL to discriminiate direction with high precision,and use small current modulation and neutralization technique to conquer the influence on the velocity measurement precision by modulation triangular signal.We use frequency-division tracking modulation to improve the dynamic range of direction discrimination and expand the dynamic range of direction discrimination to be 5～500mm/s,at the same time the reliability is better than 99.9%.(4)With the external cavity length is 30±1mm,the velocity range is between 30mm/s to 480mm/s,sampling time is 0.1s,the velocity measurement precision is better than 1%,and repeatable precision is better than 0.2%,and the reliability of direction discrimination is high.The author completes the research on the velocity measurement precision of single mode VCSEL self-mixing LDV.Highlights of the dissertation are as following:Use single mode VCSEL in place of common semiconductor LD to study LDV,and the dynamic range of external cavity length of LDV system has been improved obviously.Use difference frequency analog PLL technique to process Doppler signal to reduce the influence on velocity measurement precision by Doppler signal spectrum width and amplitude modulation envelope and to expand the tracking frequency range and the precision and dynamic range of velocity measurement have been improved.VCSEL operating current modulated by trangular wave,whose frequency is N-divided form Doppler freency,is employed for motion direction discrimination.The dynamic range of direction dircrimination is expanded by this frequency-tracking method.