  Free-space optical (FSO) communication is a promising solution to support
wireless backhaul links in emerging 6G non-terrestrial networks. At the link
level, pointing errors in FSO links can significantly impact capacity, making
accurate modeling of these errors essential for both assessing and enhancing
communication performance. In this paper, we introduce a novel model for FSO
pointing errors in unmanned aerial vehicles (UAVs) that incorporates
three-dimensional (3D) jitter, including roll, pitch, and yaw angle jittering.
We derive a probability density function for the pointing error angle based on
the relative position and posture of the UAV to the ground station. This model
is then integrated into a trajectory optimization problem designed to maximize
energy efficiency while meeting constraints on speed, acceleration, and
elevation angle. Our proposed optimization method significantly improves energy
efficiency by adjusting the UAV's flight trajectory to minimize exposure to
directions highly affected by jitter. The simulation results emphasize the
importance of using UAV-specific 3D jitter models in achieving accurate
performance measurements and effective system optimization in FSO communication
networks. Utilizing our generalized model, the optimized trajectories achieve
up to 11.8 percent higher energy efficiency compared to those derived from
conventional Gaussian pointing error models.
