Analysis And Processing Of Laser Self-mixing Interference Signal By Reflector Rotation

After laser is reflected or scattered by the external object, part of the light return to laser cavity and interfere with the laser inside, and this causes the change of laser output intensity and frequency. This phenomenon is called as self-mixing interference. With its advantage of simple and compact structure, it arouses the interest of researchers from different countries, and it is one of the most important interferometry now. Self-mixing interferometers can be applied to measure varies of physical parameters, and take the place of conventional interferometers in many kinds of situation.Information about external object lies in self-mixing interference signal, this information can be restored by proper analysis and processing of signal. This paper is primarily about analysis and processing of laser self-mixing interference signal caused by reflector rotation, and mainly has mentioned about the following things.(1) This paper studies the optical modulation index inside laser intensity formulation, the position of the collimated place is determined by analyzing the relationship between the optical modulation index and rotation angle, and collimation technique is applied to angle measurement of prism. Error is emerged when analyzing bad signal by Gaussian fitting independently. To solve this problem, self-mixing interference signal is processed by digital envelopment analysis and Gaussian fitting simultaneously. Finally, experiments of locating the place of object being collimated and collimation is carried out, the results of experiment validate these methods.(2) Reflector rotation causes the phenomenon of laser self-mixing interference. It is discovered that the increment of angle measurement range leads to the nonlinear relation between self-mixing interference signal phase and rotation angle. The angle measurement accuracy is reduced, as the nonlinearity caused pronounced errors. In order to reduce nonlinear measurement error, errors of angle measurement caused by experimental parameters are theoretically analyzed and simulations were carried out subsequently, then an experimental parameters optimization is proposed. A new method relies on nonlinear relationship to recognize the direction of rotation is introduced. Self-mixing interference experiments in angle measurement are performed and the results corresponding to different conditions were given afterwards. Precision of measurement is increased by one order of magnitude compared with non-optimized scheme, measures with a resolution of 10-5rad. Evidences for recognition of rotating direction and measurement accuracy improvement with optimization scheme adopted are provided. High accuracy of measurement maintains as angle measurement range enlarged.