Theoretical and experimental characterization of omnidirectional optical links for free space optical communications

Abstract

Optical wireless links can provide fiber-like data rates over short distances with low probability of interception and/or detection. The range of an optical wireless link depends on the transmitter power level, the receiver sensitivity, the beam divergence of the transmitter, and the level of atmospheric obscuration and beam scattering. Directional optical wireless link transmitters typically have full angle beam divergence of only a few milliradians, which can require active pointing, acquisition, and tracking in order to maintain link availability. In contrast, omnidirectional optical wireless transceivers use large angle beam divergence to provide inter-node communication capability that requires no pointing. Omnidirectional optical wireless links cannot be expected to provide the range or data rate performance of directional optical wireless links, yet they have unique capabilities that can be exploited in sensor networks, for example as data egress beacons, locator beacons, or for the guidance of munitions. In such applications they may remain in a quiescent state operating at low battery drain until called into full functionality. This paper describes the theoretical and experimental performance of omnidirectional optical wireless transceivers, especially those with relatively low data rate performance, which have potential for use in covert, deployable sensor networks. The potential range and data rates of these transceivers are analyzed in various performance scenarios; and the actual design, construction, and performance of prototype devices and optical links between them are described.