Study On The Snr Capability Optimization Of Fiber Lidar System

Fiber lidar is one of the new trend of imaging laser radar, which is compact,small size, and can be applied to a variety of complex situations. That how to improve the detection capability of fiber lidar effectively need to be considered seriously. In fiber lidar, the coupling efficiency between the antenna and fiber, as well as the heterodyne mixing efficiency between the signal light and the local vibration light, can significant influence the detection capability.Firstly, the traditional structure of fiber lidar is analyzed in this paper. A dual-detector balanced optical heterodyne receiver approach is proposed, in order to lower the effect of local vibration noise. Compared with the traditional approach, this method can effectively improve the signal to noise ratio of the system.Secondly, the mixing efficiency that affects the signal to noise ratio is studied. According to the analyses of the phase-space matching conditions, we point out that polarization matching and amplitude matching are the main factors that influence the fiber lidar heterodyne mixing efficiency. This paper calculates the polarization angle influence on the intermediate frequency current of the detector. In order to achieve polarization matching, a method of using polarization maintaining fiber is proposed. By analyzing the performance of the detector, in order to achieve amplitude matching, a method for determining the optimal local oscillating power is given.Then, the antenna-to-fiber coupling model was studied, in which the Cassegrain telescope is chosen as the receiving antenna. Then the factors that influence the coupling efficiency are analyzed. The coupling efficiency between the Cassegrain telescope and the fiber is calculated. The result shows that the coupling efficiency is affected by the obscuration ratio, the aperture size and the fiber mode field radius. Then we calculate the decrease of the coupling efficiency in detail at the condition of lateral displacement and axial displacement. The results show that coupling efficiency is sensitive to lateral displacement.In the end of this paper, we design a Cassegrain telescope by optical design software ZEMAX, and the simulation in the condition of lateral displacement and axial displacement is given. As can be seen by comparing, the simulation results match the theoretical calculated results.