Highly sensitive fiber coupling for free-space optical communications based on an adaptive coherent fiber coupler

In this paper, we present the result that the performances of the highly sensitive adaptive coherent fiber coupling (ACFC) technology, which consists of a movable fiber tip and a coherent detector. The ACFC technology is applied for the free-space coherent optical communication systems especially with a long distance link such as the satellite to ground, and it is used for compensating the tiny random angular jitter caused by the vibration of the receiver and the residual jitter error of the adaptive optics unit which is used for alleviating the effect of turbulence. Compared with the traditional fiber coupling using direct detection, the advantages of ACFC technology has been verified by analyzing the SNR value. The result shows that the receiver sensitivity can be enhanced by up to 20 dB. The residual jitter error of a free-space optical receiver with a 357-element AO unit is acquainted, and it is used for verifying the performance of the ACFC technology. The result shows that the average coupling efficiency is 73.2% with a mean square error (MSE) 1.12%, increasing significantly compared with the average coupling efficiency 50.1% and a MSE 7.43% without ACFC correction.