Wide-Field Laser Nutation FSOC System Enabled by Multi-Core Fiber

Free-space optical communication (FSOC) is a key technology for sixth-generation (6G) networks. To achieve high coupling efficiency for the single mode fiber (SMF) receiver, conventional beam alignment methods typically require splitting the received signal beam to measure the angular deviation relative to the fiber center, leading to additional optical power loss and system complexity. Although laser nutation algorithms allow precise alignment without beam splitting, their narrow field of view (FOV) limits their applicability. We propose a wide-field nutation system with multi-core fiber (MCF), achieving a common optical path FSOC architecture that removes the need for a separate detection optical branch. An enhanced laser nutation algorithm is developed to extend its FOV by utilizing the structure characteristics of MCF. A framework for MCF-based beam alignment is established to improve the convergence ability. Experimental validation is conducted to optimize the operational parameters of the laser nutation process, achieving a fine alignment FOV of$\pm$2.4 mrad. Finally, a 3.71 km lake-crossing experiment was conducted, achieving automatic alignment with a link loss of 31.25 dB and stable coherent communication at 8 and 16 Gbps, error-free without forward error correction.