FSM-based PAT using Cartesian Coordinate Information

In this work, we present a pointing, acquisition, and tracking (PAT) algorithm based on a fast steering mirror (FSM), which operates using Cartesian coordinate information. The algorithm first computes the initial steering angles of the FSM to align the optical beam between a transmitter-receiver pair, based on their three-dimensional position vectors. Fine alignment is subsequently performed using real-time feedback from a quadrant photodiode (QPD), enabling precise correction of residual pointing errors. The proposed method is experimentally validated in a static indoor testbed, demonstrating accurate and stable beam alignment.