Develop the fiber coupling efficiency based on SPGD control algorithm

In the satellite-to-ground laser communication, the beacon light is affected by atmospheric turbulence, atmospheric scattering and atmospheric absorption, so there is a coupling error. And the receiving end of ATP system is affected by random disturbance which lead to the initial coupling place change. The above reasons resulting in the fiber coupling energy decline. The efficiency of fiber coupling directly affects the success rate of decoding, so it is important to improve the efficiency of fiber coupling. This paper uses a tilt mirror which has cheaper cost and simple structure compared to wavefront corrector as the actuator for optical fiber coupling alignment and use the two-dimensional stochastic parallel gradient descent algorithm (SPGD algorithm) widely used in the field of adaptive optics to correct the coupling errors caused by atmospheric turbulence and random disturbance at the receiving end. The SPGD algorithm is affected by the initial coupling position, when the initial coupling position is unreasonable, the SPGD algorithm cannot be used for effective coupling. Therefore, the CCD camera is used as a position sensor to obtain a reasonable initial coupling position and improve the fiber coupling efficiency of the system.