The Study And Experiment Based On Special External Cavity Structure Of Self-Mixing Interference

Laser self-mixing interference(LSMI) is also called optical feedback self-mixing interference or injected modulation effect, it refers to the light output of a laser source is reflected or scattered by an external object, a portion of the reflected light feedback back to laser cavity. The feedback light which carries information of the external object and then mixes with the light inside laser cavity, and modulates the output of laser such as power and frequency. The signal of LSMI have some similarities with the signal of traditional double-beam interference, but its characteristics are different from the traditional interference, does not conform to the traditional interference theory, which is called the new interferometric techniques. Compared to the traditional interference measurement system the system of LSMI has a lot of advantages such as simple structure, easy to collimation, optical path is compact, low cost. Whereby the LSMI technology has been the attention of the scholars, and is widely used in the measurement field.Recently, the following research areas draw many attentions of researchers:(1) applications of LSMI in the measurement field; (2) the research of LSMI by applying different types of light source; (3) using of a variety of signal processing methods to improve the measurement accuracy of the LSMI scheme. However few scholar study the LSMI with special feedback external. In this paper, we studies the LSMI with confocal external cavity and the LSMI with multiway feedback external cavity. First, we using the principle of confocal laser microscopy(CLM), the principle of Fourier optical and the principle of confocal to analyze the LSMI with confocal external cavity in theory, and some simulation analysis is made according to the theory. Simultaneously, the experiment is made to verify the validity of the theoretical and simulation. From the simulation and experiment, it is find that the signal envelope of LSMI with confocal external cavity is similar to the axial response cure of CLM. When the numerical aperture of the lens is less than the predetermined value and the amplitude of the object is smaller, the signal of LSMI with confocal external cavity is similar to the signal of conventional LSMI. Then the self-mixing interference (SMI) effect with multiway feedback is analyzed in this paper. The basic theory of SMI with multiway feedback external cavity (MFEC) can be derived from the theory of interference as well as the theory of laser self-mixing interference (LSMI). Based on the external cavity structure with MFEC, a SMI model with two feedback external cavity structure is proposed. The expressions of the phase and output power in the MFEC are deduced and some simulation analyses are made. It is found that the output signal of the SMI system with two external cavity is sinusoidal or sawtooth waves, which is similar to the signal of SMI with a low frequency sinusoidal phase modulation. The density of interference signal fringes is uneven in one period and the shape of the interference wave is determined by the intensity of the external feedback.Finally, we have built the experiment system of LSMI with confocal external cavity and LSMI with multiway feedback external cavity, which includes the control of PZT and the use of signal acquisition system. In view of the problems arising from the experiment, some methods are proposed, then the interference that might arise in the experiment are discussed.