Double feedback self-mixing interference under moderate feedback of misalignment cavity

In order to study the influence of the multiple feedback on the self-mixing interference in laser diodes, double feedback effect and double frequency fringes phenomena were analyzed based on the three-mirror F-P model. After simulation, it is found that when the relative intensity η of the second trip light to the first is big enough, the image of interference can be recognized, and the two interferential signals of two trips can be distinguished by differential coefficients. The sensitivity of system can reach the value of λ/4. The phase differences affect the interference pattern. Experimental results are in good agreement with the simulation results. Experiments also validate the double frequency fringes phenomena, caused by the misalignment external reflector, could coupling the second trip light into laser without first trip. These obtained conclusions are helpful for improving the sensitivity of the system and judging whether the external cavity is alignment.