Research for a type of aspheric E-H hollow beam shaping and fiber-coupled defocus characteristics

The integration of space optical communication and fiber optical system plays a vital role in satellite communications and deep space exploration. However, achieving efficient fiber coupling under defocus conditions remains a key challenge. Consequently, a new, to our knowledge, aspheric shaping lens set composed of elliptical and hyperboloidal (E-H) surfaces is proposed in this study. This E-H lens set transforms the hollow beam emitted from the receiving end of a Cassegrain antenna into a solid beam, thereby reducing the loss of central energy inherent in hollow beam transmission. An optical system incorporating the Cassegrain antenna and the aspheric lens set is designed, with the lens surface equations derived based on the principle of equal optical path. Furthermore, considering chamfer design and Fresnel reflection loss, a new, to our knowledge, hyperbolic Fresnel (H-F) coupling lens is researched. This system achieves a coupling efficiency of 79.55% for a fiber mode field radius of 5 µm, with fiber defocus ranges of 2.36 µm (lateral offset), 68.34 µm (longitudinal offset), and 47.24 mrad (angular jitter). Importantly, within these defocus ranges, offsets of the optical fiber receiver do not cause a significant variation in the coupling efficiency of the optical communication system.