Modeling and performance analysis for few-mode free-space optical communication reception based on optical-domain coherent beam combining

This paper proposes a theoretical model for a few-mode free-space optical communication (FSOC) reception based on optical-domain coherent beam combining. By analyzing the coupling efficiency of few-mode fiber, the relationship between atmospheric turbulence and coherent beam combining is established. The bit error rate (BER) performance is quantitatively evaluated by incorporating device loss factors and combining efficiency, thereby constructing a comprehensive theoretical framework that encompasses turbulent disturbance, mode coupling, and optical-domain beam combining across the entire signal transmission chain. Simulation and experimental results demonstrate that at a BER of 3.8×10⁻³, the proposed scheme achieves a 1–3 dB improvement in receiver sensitivity compared to single-mode FSOC systems, while performing within 1 dB of systems utilizing mode diversity reception technology. Moreover, the scheme requires only a single local oscillator and a single high-speed detector, significantly reducing the hardware complexity and noise accumulation associated with multi-branch detection.