Optimized 2 μm FSO systems through PAM and adaptive equalization algorithms for enhanced transmission reliability

This study demonstrates significant performance enhancement for 2 μm freespace optical (FSO) communication systems by integrating four-level pulse amplitude modulation (PAM4) with a novel fractional-order normalized least mean square (FNLMS) equalization algorithm. Simulation results indicate that a 25 GBaud/s PAM4 signal transmitted over a 3 km atmospheric link under moderate turbulence achieves a bit error rate (BER) of 7.9×10 -4 , comfortably below the hard-decision forward error correction (FEC) threshold of 3.8×10 -3 . Experimental validation conducted on an indoor FSO platform confirms the algorithm's effectiveness. Notably, the FNLMS algorithm reduces computational complexity by 41.16% compared to the conventional Volterra equalizer while delivering comparable performance. This work provides a viable solution for nextgeneration optical communication systems, addressing critical demands for secure, highcapacity, and energy-efficient wireless connectivity, and underscores the potential of 2 μm FSO-PAM4 integration in future communication infrastructures.