240 Gbps SI-FMF/FSO communication system based on LP modes and PV code with the impact of foggy weather in Alexandria and Setif.

This paper presents a novel, to the best of our knowledge, high-speed optical communication system achieving a 240 Gbps transmission capacity by integrating step-index few-mode fiber (SI-MMF) and free space optics (FSO). Knowing that Hermite-Gaussian modes (HGMs) are eigenmodes of a free space medium and the linearly polarized modes (LPMs) are eigenmodes of step-index few-mode fiber (SI-FMF), and by considering the similarity between HGM ( and ) and LPM ( and ), respectively, the system employs dual-polarization (DP) and linearly polarized (LP) modes (, , and ), combined with optical code division multiple access (OCDMA) using permutation vector (PV) codes. Each polarization state carries data from three LP modes, with each mode supporting four OCDMA channels, each assigned a unique PV code. The system's performance is evaluated under varying fog conditions using key metrics such as quality-factor (Q-factor), bit error rate (BER), and eye diagrams, which provide a comprehensive assessment of signal strength and quality. Real-world applicability is assessed using meteorological data from two African cities, Alexandria, Egypt, and Setif, Algeria. System performance is characterized using the Q-factor, bit error rate (BER), and eye diagrams. The results show that, in Alexandria, successful transmission is achieved over 1.41 km. In Setif, the transmission distance is reduced to 1.31 km due to slightly higher atmospheric attenuation. These ranges are observed at a BER below and a Q-factor exceeding 3.10. Consequently, these findings confirm the viability of the proposed system for high-capacity optical communication in challenging weather conditions, making it suitable for future 6G networks.