Advanced Thresholding Method for Pointing in Free Space Optical Communication

The pointing efficacy of terrestrial auto-aligning Free Space Optics (FSO) links depends on the positioning system's precision and the optical component's properties. The positioning system determines the size of the area to be scanned to locate the optical beam from its counterpart, while the beam's divergence and the parameters of the receiving optics affect the scanning speed. In terrestrial FSO communication, transmitted optical power must comply with safety standards, limiting transmission power and potentially making it difficult to reliably locate the counterpart's optical beam using the conventional Power Thresholding Method (PTM). To address this, the article proposes a novel Advanced Thresholding Method (ATM) that uses a four-quadrant photodiode as a position-sensitive sensor. By incorporating gimbal deviations, photodiode coordinates, and a transfer function, this method enhances the ability to detect optical beams with lower optical power, improving the reliability of the scanning process compared to the traditional PTM.