Advanced multi-feedback stochastic parallel gradient descent wavefront correction in free-space optical communication

The stochastic parallel gradient descent (SPGD) method has been deeply explored to correct atmospheric turbulence in free-space optical communication. However, SPGD is usually trapped in the problems of sub-optimization and long-time iteration because the controlling signals can be updated merely by the local gradient derived from the Strehl ratio (SR). This research proposes an advanced multi-feedback SPGD (AMF-SPGD) method to strengthen the wavefront aberration correction performance. With the aid of multiplexed computer-generated hologram (CGH), a spot array will be captured thus a corresponding SR array is subsequently obtained, which provides the multi-feedback suggesting the more abundant optimized information. By adequately integrating the global and local gradient, AMF-SPGD could timely adjust the search gradients and achieve the optimum with a greater probability. The system principle and pipeline of the AMF-SPGD will be illustrated in detail. Subsequently, extensive simulations will be conducted to verify the significant upgrade in performance, including the search speed, SR and bit error rate (BER).