Free-space optics to replace RF links in orbital apps

Discovery Semiconductor Inc. has showcased 10Gbit/s free-space optical links in tests at Kirtland Air Force Base in New Mexico. The tests were carried out under the supervision of the Air Force Research Labs' Space Vehicles Directorate, which is looking into substituting RF links with free space optics (FSOs) in some inter-satellite link (ISL) designs.

Christoph Wree, program manager, Discovery, said the company has already worked on many different modulation schemes, but the return-to-zero differential phase shift keying modulation employed in the given has the best resilience, particularly in the atmosphere, where scintillation effects must be overcome.

The company has offered the full transceiver subsystem, operating at 1550nm. Science Applications International Corp. partnered in the system testing, while Schafer Corp. worked together in analysis and management services.

The series of tests, done several months ago in New Mexico, showed a receiver sensitivity of 27 photons per bit, and a BER of 1e-9, a result that is only five photons away from the quantum limit. This indicated that FSO links can overcome losses either in the long distances in orbital ISL applications or in atmospheric turbulence during airborne applications.

- Loring Wirbel
EE Times