Laboratory Demonstration of Optimizing Optical Single Sideband Scheme to Increase Spectral Efficiency in Optical Geostationary Satellite Feeder Links

摘要

Optical geostationary orbit (GEO) satellites are one of the means to provide high speed internet and broadband services to even remote areas on the globe. However, the optical beam, as it propagates through the atmosphere, is affected by the atmospheric index of refraction turbulence and pointing errors due to beam wander and mechanical vibrations on the platform which result in fading, hence loss of signal. We present transmit diversity as a fading mitigation technique and use wavelength division to minimize cross interference between the transmitted signals. Optical single sideband (OSSB) scheme is used to increase spectral efficiency (SE) of the system. We demonstrate a scheme where an OSSB signal is produced using commercially available optical filter with tunable bandwidth and center frequency. For a 32Gbps data signal modulated using amplitude shift keying (ASK), we measure the required minimum 6dB and 20dB bandwidths of the optical filter to be 12GHz and 24GHz, respectively. Also, the offset of the filter from the carrier is found to be -11GHz and +10GHz to produce an error free lower and upper OSSB signal, respectively. The SE of the OSSB signal is found to be 1.34 bit/s/Hz. Moreover the stability of the optical filters and carrier ensure reliable signal generation making the OSSB a potential candidate to be used in future free space optical links.