OCTOBER 2, 2008 -- Discovery Semiconductors Inc. (search for Discovery Semiconductors), Air Force Research Laboratory, Space Vehicles Directorate (AFRL/RV), Science Applications International Corp. (SAIC), and Schafer Corp. have collaborated on a 10-Gbit/sec free space optical (search for FSO) communications link. According to the companies, more than 80 dB of link loss can be overcome with this system.
"The 10-Gbit/sec system uses a wavelength of 1550 nm where powerful optical amplifiers can be used to boost the transmitted signal and pre-amplify the received signal," explains Dr. Christoph Wree, program manager at Discovery Semiconductors. "The use of differential phase-shift keying [DPSK] gave us an excellent receiver sensitivity of 27 photons/bit at a bit error ratio of 1e-9. This is only 5 photons away from the quantum limit," he notes.
Patrick Collier from SAIC tested the system at the Kirtland Air Force Base in the presence of atmospheric turbulence. "In comparison to other investigated modulation formats, RZ-DPSK showed the best resilience against scintillation effects introduced by atmospheric effects," he reports.
The use of FSO communication links allows the Air Force to increase the data rate and reduce the space, weight, and power consumption with respect to RF communication links. This FSO project demonstrates that the system can overcome large link losses, which can be introduced either by ultra long inter-satellite link distances or by link losses arising from atmospheric turbulence, say the companies, who believe the 10-Gbit/sec RZ-DPSK system is a promising candidate for future FSO communication links.