Operational condition for direct single-mode-fiber coupled free-space optical terminal under strong atmospheric turbulence

Abstract

The author describes the key design feature of a newly developed compact free-space optical terminal, which can achieve robust direct single-mode-fiber-coupling with advanced bidirectional beacon tracking system and excellent operational performance under various adverse weather conditions, such as strong atmospheric turbulences and rain/snow falls. The author found that there is a good correlation between the scintillation index of beacon/signal receiving intensities and the signal fading depth. Therefore, the signal link quality can be predicted from the beacon scintillation index using the classical Rytov theory. According to the outdoor experimental results, it can be concluded that the scintillation index of the beacon beam should be less than 0.1 for stable and reliable communication links.