Nulling strategies for preventing interference and interception of free space optical communication

Free space optical systems can transmit at high data rates and can provide cheap, easily deployable solutions for both short-term and long-term communication needs. Controlling the direction of energy propagation from the optical transmitter can prevent communication between two users from interfering with another user in an optical network and can reduce the susceptibility of the system to eavesdropping. This paper discusses a method to maximize the power transmitted from an optical aperture array to the intended receiver of a free space optical link while limiting the power transmitted to a defined region within the main lobe of the transmission. We find that it is possible to suppress by over 10 dB the power to a region as close as 0.2 beamwidths away from the receiver without compromising the ability of the intended user to receive the signal.