Introduction
Satellite communication through laser is a fast-emerging technology for future space information networks. It offers immensely faster data rates, broad bandwidths, enhanced security, and a low size-weight-power terminal when compared with the traditional radio frequency (RF) systems. The high orbit links are of immense value. They offer continuous global coverage, real-time Earth observation data downlink, and deep-space relay, but they remain among the most difficult to implement reliably. The beam must travel very long distances through vacuum and then penetrate the entire atmospheric column during which it experiences strong scintillation, beam wander, and angle fluctuations caused by the atmospheric turbulence. The effect causes power fading and distortions of the wave front. This in turn severely degrades the single-mode fibre coupling efficiency and coherent detection performance.
