Modelling and analysis of QPD based track sensor developed for inter-satellite optical communication

Free Space Optical Communication (FSO) is an emerging and promising technology that utilizes optical signals to transmit data through free space. It offers several advantages, including high data rates, low latency, security, and immunity to electromagnetic interference. FSO systems find applications in various fields, including telecommunications, satellite communication, disaster recovery, and military operations. Utilizing lasers for free space optical communication presents an appealing alternative to conventional radio frequency (RF) communication methods, particularly in managing substantial data volumes while simultaneously reducing size, weight, and power (SWaP) requirements. Among the formidable challenges in the realm of satellite-based optical communication systems lies the necessity for highly precise acquisition and tracking of target satellites. Quad Photodetector (QPD) tracking sensors stand out as the preferred choice for discerning angular positions due to their rapid responsiveness and excellent accuracy. In this paper, we expound upon the operational principles and mathematical modelling of QPD-based tracking sensors, aiming to attain optimal sensitivity and meet predefined field of view (FOV) specifications. Additionally, we elucidate the focusing technique, detail the testing setup, and present the achieved outcomes of the tracking sensor.