Degradation of single-mode fiber coupling efficiency due to localized wavefront aberrations in free-space laser communications

Coupling efficiency of coherent plane waves into single-mode fibers is degraded by the localized deformation of the optics antenna used for reception of optical beams. For transmission-type and reflection-type antennas, the evolution of coupling efficiency with the change of characteristic parameters of the localized distortion are investigated. It is found that the coupling efficiency varies regularly as the increase of the normalized center deepness h/R, the normalized radius a/R, and the normalized center distance d/R. The key principles for selecting optics are determined. The results obtained will be useful in estimation and design of fiber-coupled optical systems in free-space communications.