Adaptive gain spatial receiver for wide dynamic range communication links

Abstract

Wireless optical communication facilitates high-speed transmission across long distances. However, time-varying and spatially-dependent attenuation through freespace channels due to scattering impedes operation for many wide dynamic range links. In the atmosphere, communication is often limited to short transmission times when optimal power is delivered to the detector, as the distance and channel conditions between ground terminals and airborne or space systems changes constantly. This effect is even more apparent in oceans, where optical attenuation varies so drastically that it has hindered practical implementation of high-speed communication undersea. To accommodate the wide range of input powers, a novel adaptive gain spatial receiver is developed in this thesis. The designed device replaces multiple detector functions of an existing underwater laser communication system with an adjustable gain and sensitivity receiver for long-range or high-rate transmissions. The novel receiver also provides spatial resolution for improved efficiency and performance. In preliminary laboratory tests, a proof-of-concept setup validates simulation expectations and informs future terminal integration. Using the new system, a wide range of input power across six orders of magnitude down to single photon detection and data rates up to 1Gb/s are attainable, which will enable future tests in the open ocean.