Research On Self-mixing Small Angle Measurement And Related Technology

Laser self-mixing interference effect occurs when the light back-reflected or back-scattered from external object and reenters the laser cavity, the reflecting light then mixing with the light inside the cavity, causing the modulation of output characteristics. Then the measurement of the physical quantity of the target will be achieved. Compared with the traditional interference technique, self-mixing interference has just one interference channel, simple and compact structure, self-aligning, high sensitivity. So it has been employed widely in the field of industrial measurement, scientific research, national defense and so on. We put forward an angle measurement system which can be applicable to the occasion with high requisition of resolution and range based on the self-mixing interference effect and the characteristics of the right-angle prism. The measurement range of the angle measurement system can reach 21.49 mrad and the resolution can reach 0.55 mrad. In addition, we also studied the external objects scattering property and the fiber ring laser with different fiber-ends, which provide a theoretical guidance and experimental support for the optimization of the laser self-mixing interference system. The research work we have devoted to this paper mainly include the following aspects:1. Here we proposed a novel self-mixing angle measurement system with high resolution and wide range, and gave the basic theoretical analysis and numerical simulation results with different wavelength of laser source.2. According to the theoretical analysis, an experiment device was designed and built successfully. In addition, the experimental phenomena of lasers with different wavelength as the light source were observed, the analysis results of experimental phenomena and the relative angle error were given in the paper, which laid a foundation for the next step of the system optimization and improvement.3. The influence of different external objects scattering property on the self-mixing interference technology were analyzed and discussed. Theoretical and experimental results show that the scattering ratios and SNR of the reflective film are mostly bigger than the other scattering surfaces, and the mean SNR values of self-mixing signal demonstrate decline characteristic as the incident angle increases.4. We have performed related research on different fiber-ends as the light collection structure. It can be obtained that different fiber-ends have different coupling efficiency, different structures have different application advantages in measurements by comparing the experimental phenomenon and the theoretical results.The followings are the innovative points in this paper:1. We carried out a new small-angle measurement experiment based on the self-mixing interference. By using the characteristics of the right-angle prism that the incident light is parallel to the emergent light can overcome the issues of traditional method, such as low sensitivity and limited range.2. As a consequence, the measurement range and the resolution of MSL as light source in the angle measurement system can reach 18.90 mrad and 0.55 mrad, while the range and the resolution of He-Ne laser can up to 21.49 mrad and 0.61 mrad.3. In the study of the external objects scattering property, the SNR of the self-mixing signal can be enhanced by using a reflective film and choosing a suitable angle can help us eliminate the bad effect caused by speckle pattern partially, which provide a foundation for the optimization of the laser self-mixing interference system.4. In the theoretical part of the influence of different fiber-ends on the laser self-mixing signal, we use the ABCD matrix under paraxial approximation for the calculation of coupling efficiency inside the fiber ring laser with different fiber-ends.