Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1997 · 112 citations · 0 references
Natural SciencesElectrical EngineeringPhysicsAtmospheric RadiationOpticsPhotonicsAtmospheric CorrectionFree-space OpticsLaser OpticsLaser PhysicsOptical Communication SystemsAtmospheric Error CorrectionAtmospheric ScintillationBeacon TechnologyGround-to-satellite Optical LinksSatellite Free-space Optical LinksScintillationScintillation MechanismsScintillation Mitigation
Uplink scintillation severely hampers laser communication between satellites and ground stations. The study aimed to identify how many and how spaced separate transmitters are needed to reduce atmospheric scintillation‑induced power fluctuations to acceptable levels. Multiple independent lasers from separate apertures were transmitted and their incoherent sum at the satellite was measured over 1.2‑ and 10.4‑km horizontal links to emulate uplink atmospheric scintillation. Increasing the number of transmitters from 1 to 16 reduced signal fluctuations, and a 16‑laser ground terminal on an 18‑inch circle with a 7‑dB fade margin can adequately compensate for scintillation fades, with remaining deep fades addressable via forward error correction.
Uplink scintillation is a serious issue for laser communication between a satellite and the ground. Fluctuations on the uplinked beacon and communications laser can be minimized by transmitting multiple independent lasers from separate apertures which then sum incoherently at the satellite. The objective of the experiment described here was to determine the number and spacing required for separate transmitters to reduce fluctuations in the received power due to atmospheric scintillation to acceptable levels. Received power vs. time data were collected for horizontal laser links established between a laser transmitting platform and a receive telescope assembly separated by distances of 1.2 and 10.4 km to mimic the expected atmospheric effects of an uplink slant path to a satellite. Reduction in signal fluctuations was observed as the number of laser transmitters was increased from 1 to 16. A ground terminal design with 16 lasers on an 18 inch diameter circle with a 7 dB fade margin should be adequate to compensate form sot scintillation fades, while the remaining deep fades may be corrected by using forward error correction techniques.