Detection and correction of optical axis misalignment in an atmospheric optical communication link

Atmospheric optical communication (AOC) is a critical frontier for next generation communication. Nevertheless, the performance of AOC is not only impacted by atmospheric effects but also significantly by optical axis misalignment. Therefore, AOC terminals have to frequently return to the laboratory to calibrate optical axis misalignment. In order to reduce the frequency of laboratory calibration, this paper establishes and experimentally validates a novel method for detecting and correcting optical axis misalignment in the AOC link. The proposed method is based on four photodetectors symmetrically arranged around the receiver's optical axis. Based on the power fluctuations detection and average power statistics from four photodetectors, the horizontal and vertical optical axis misalignments from the transmitter can be detected. Then, the optical axis misalignments can be corrected by adjusting the beam propagation directions of the transmitter. The experimental results show that the optical axis misalignments can be corrected to 1.8 <i>µrad</i> at 2.4 <i>km</i>. The proposed method is very simple and efficient, which is beneficial for enhancing the operational period of AOC terminals under the environmental variations.