Study On The Processing Method Of Laser Self-mixing Interference Signal With Two Feedback External Cavity

Optical feedback self-mixing interference(OFSMI) refers to the output of laser which is reflected or scattered by external object, the part of optical feedback back to the laser resonant cavity, mixing with lumen light, leading to the change of output power and frequency, and forming the self-mixing interference effect. The SMI is similar to the traditional double-beam interference, but it is different from the traditional interference in theory, and the characteristic is different between SMI and traditional interference theory. Compared to the traditional interference measurement,the OFSMI has simple structure, easy collimation, low cost and compact light path etc.At present, the self-mixing interference phenomenon research further. But the theory research of laser self-mixing interference with special structure external cavity is not enough. Therefore, this article focuses on the laser self-mixing interference with two feedback external cavity. The laser self-mixing interference with two feedback external cavity is similar to the laser self-mixing interference with multiple external cavity. The difference is that the every road of laser self-mixing interference with two feedback external cavity will carry a movement information. This can achieve measurement of two goals at the same time . Now, the self-mixing interference with special structure has only carried on the theoretical analysis and experimental observation. Now, because of the processing method of self-mixing interference signal has not sufficient research. Under the weak feedback level, the article studies on the processing method of self-mixing interference signal by analysing the model of laser self-mixing interference with two feedback external cavity. First, realizing the reconstruction of self-mixing interference signal phase with two feedback by using the Hilbert. Then getting the frequency spectrum of the reconstructed signal phase by FFT and the two-way signal spectrum respectively by filter. Finally, recovering the time domain waveform of the two-way signal spectrum by IFFT. At the same time, this paper presents the Wavelet soft threshold and EEMD combining algorithm to reduce the interference of self-mixing interference signal with noise and improve the accuracy of displacement measurement.Through the simulation analysis and processing the experiment acquisition signal verifyes the effectiveness and applicability. In addition, we built the OFSMI with one feedback external cavity and the OFSMI with two feedback external cavity. Mainly for the using of PZT, DS102 and signal acquisition system are briefly introduced. To simple problems in the experimental process, and the corresponding solutions are proposed.