Influence of photoelectric conversion noise on closed-loop performance of adaptive SMF coupling device

The single-mode fiber (SMF) adaptive coupling device can efficiently and stably couple the space laser into SMF, which plays an important role in the fiber-based free space optical communication (FSOC) technology. Therefore, a novel corrector named adaptive fiber coupler (AFC) is developed and successfully used in the adaptive SMF coupling applications. However, in the FSOC system under long-range turbulent atmosphere, the closed loop performance of AFC will be seriously disturbed by the photoelectric conversion noise. This problem is studied in depth in this paper. The operational principle of the photoelectric conversion noise is analyzed, and the corresponding evaluation index isgiven. Furthermore, The numerical simulation experiments are conducted to study the specific influence of the photoelectric conversion noise. The results show that the averaged closed-loop coupling efficiency, control accuracy, and control bandwidth of AFC are seriously affected. According to the results, the empirical formula is given. This formula can be used to calculate the optical and electrical parameters that the AFC device should meet under the condition of strong noise interference. The theoretical and simulation results in this paper can provide a theoretical basis for designing the AFC device under long-range turbulent atmosphere.