Communication- and physics-adaptive carrierless phase-retrieval reception for LEO satellite-to-ground FSO communications.

In this paper, we propose and experimentally validate a communication- and physics-adaptive phase retrieval (CP-APR) scheme for low-Earth-orbit (LEO) satellite-to-ground free-space optical (FSO) links. The proposed method establishes a unified carrierless phase-retrieval framework by jointly incorporating a soft-projection relaxed averaged alternating reflections (S-RAAR) backbone, adaptive physical dispersion tuning, a constellation-constrained communication prior, and an adaptive spectral-phase constraint (ASPC), enabling robust full-field reconstruction from intensity-only measurements. To validate its practical feasibility, a ground-based indoor equivalent-link experiment is performed using a custom-built fiber-optic-sampled bidirectional dual-terminal FSO equivalent link, and the transmission performance is further evaluated under turbulence-impaired conditions. Experimental results show that, for 16QAM 10-Gbaud transmission over equivalent distances of 300, 400, and 500 km, the proposed scheme achieves Q-factor improvements of 16.01, 14.96, and 14.71 dB, respectively, compared with intensity modulation/direct detection (IM/DD). In addition, a gross bit rate of 42 Gbps is achieved at 500 km under the 7% hard-decision forward error correction threshold. These results validate the feasibility of CP-APR reception in the tested equivalent LEO satellite-to-ground FSO links and suggest its potential as a direct-detection-based, LO-free, coherent-compatible, and hardware-simplified solution for future satellite-to-ground optical links.