Demonstration system and applications for compact wireless ultraviolet communications

In battlefield situations, as well as other distributed sensing applications, networks of small, low-cost wireless sensors require short-range communication links that are low-power and difficult to detect at standoff distances (covert). Currently, short-range (< 100m) state-of-the-art ground-to-ground radio frequency (RF) links require line-of-sight for reliable connectivity, and may require 50 to 100 times more power for the transceiver electronics than what is radiated by the transmitter. Furthermore, the RF transmit power necessary to overcome R4 losses near the ground makes the links easily detectable at stand-off ranges unless sophisticated waveforms or highly directive antennas are employed, both of which are inconsistent with low-cost, low-power transceivers. In contrast, baseband optical communication links in the mid-ultraviolet (UV) band can exploit atmospheric scattering to achieve non line-of-sight (NLOS) operation with low-power transceivers at wavelengths that are difficult to detect at stand-off ranges. This paper reviews NLOS UV communication concepts, phenomenology, and the evolution of device technology. A portable communications test bed is described, and recent outdoor tests with 340nm semiconductor emitters are summarized. An indoor FM voice link is described, as an example of the compact form-factor that can be achieved with current technology. The paper concludes with a discussion of potential applications.