Efficiency-enhanced MPAI-optimized LG beam transmitting and receiving Cassegrain systems under atmospheric turbulence

This paper presents an efficient multi-parameter alternating iteration (MPAI) optimization framework for the joint optimization of key parameters in Cassegrain transmitting and receiving systems. A closed-form analytical expression of the optical field of Laguerre-Gaussian (LG) beams propagating through Cassegrain antennas is derived, together with analytical formulations for the detection probabilities of multiple azimuthal orders of orbital angular momentum (OAM) modes. Based on these formulations, the proposed MPAI algorithm alternately optimizes the occlusion ratio and the secondary mirror radius under turbulent conditions. Analysis and simulation results show that, for extremely complex closed-form models under turbulence, the MPAI algorithm has the advantages of low computational complexity, high efficiency, high accuracy and strong scalability. The variance of the optimized parameters is maintained below 0.1%, demonstrating excellent robustness. The average transmission distance of the system is extended from 2428.6 to 3373.4 m, corresponding to a 38.90% improvement in transmission efficiency. Furthermore, at a propagation distance of 3000 m, the detection probability of the OAM mode with l=1 remains approximately 50%, with relatively low inter-mode crosstalk. This work provides a general and scalable framework for efficient multi-parameter optimization in OAM-based free-space optical communication systems operating under turbulence.