Experimental Demonstration of a Single-Mode Fiber Coupling Over a 1 km Urban Path with Adaptive Optics

In free-space optical communication (FSOC), it is necessary to couple optical fibers for application in optical-fiber technology and devices. However, propagation through atmospheric turbulence degrades the single-mode-fiber coupling efficiency (CE). This degradation can be compensated by an adaptive optics (AO) system. In this paper, we analyze the influence of spatial and temporal characteristics of turbulence on the CE. Experiments along a 1 km urban link demonstrate that the CE increases from 5% without AO to 10%–25% in the AO closed loop at different times of day. We obtain an increase by factor 4 in the CE under weak turbulence conditions.