Concepts for wide band `bent-pipe´ optical crosslinks

Inter-satellite crosslinks are attracting a great interest because they offer privacy and reduce the need for vulnerable and expensive foreign ground stations. Optical crosslinks, using significantly improved laser transmitters, are becoming the favored solution for crosslinks having data rates greater than 1 Mbps due to reduced terminal size and integration simplicity. Optical up/down links are also feasible but require several widely separated ground entry points to assure continuous connectivity through poor weather. Optical up/down links may be a viable approach for some applications but, in general, the next generation satellites are expected to have RF up/down links and optical crosslinks. This hybrid approach requires trade studies to find an efficient interface between the RF up/down link frequencies and the optical crosslink frequencies. The authors examine optical crosslinks concepts for a satellite communication architecture that is designed to be bent-pipe, that is, the signal is not demodulated to baseband, but rather frequency translated to the next transmit frequency. The conclusion is reached that for bent-pipe optical crosslinks carrying tens of megabits per second, the technology is ready, while for higher rate systems the projected terminal sizes are favorable, but further space qualifiable component and subsystem level demonstrations are necessary to ensure successful deployment