Beam-Shape-Based Angle-of-Arrival Estimation in Free-Space Laser Communication

A novel technique is proposed for estimating the angle-of-arrival (AOA) in free-space laser communication based on the shape of a laser beam spot on a flat surface. Two methods are introduced: one where ellipses are fitted to the intensity contour of the beam spot, and another where a least-squares fit of an AOA-dependent two-dimensional Gaussian distribution is applied to the intensity distribution. The effects of beam displacement, discretization, and noise on estimation performance are analyzed. The Cramér-Rao lower bound is derived and examined in relation to the true AOA. Both methods are verified through numerical simulations and experiments. For experimental validation, a novel beam sampling technique using a liquid-crystal display and a single photodiode is developed.