A low SWaP-C pointing and tracking architecture for free space optical communications between aerial platforms

Free space optical communications are emerging as an alternative to radio as the RF spectrum becomes increasingly congested and unavailable. Secure communications at far higher data rates than radio are theoretically possible in the optical domain, however this is made difficult by the presence of attenuation and misalignment failures which necessitate advanced beam steering techniques. For communications between aerial platforms such as drones, constraints on the size, weight and power of beam steering systems become prohibitive. Developing beam steering systems which are light, compact and efficient is the key to unlocking optical communications on mobile platforms. Here, we demonstrate closed loop pointing and tracking of a moving retroreflector target using cheap and lightweight components, directed by an Arduino Due microcontroller. The system is found to be capable of tracking targets moving at up to 100 milliradians per second, and is fundamentally limited by the dynamics of the mirror. Metrics of time spent optimally aligned, root-mean-square distance from target centre and statistical analyses of beam position are used to assess the feasibility of the system. We show that in a retroreflector configuration the system spends 100% of the measured interval within 0.1 milliradian of perfect alignment at angular velocities up to 90 milliradians per second.