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Abstract The reliability and efficiency of free space optics (FSO) systems is significantly degraded by attenuation caused by different climate conditions and atmospheric turbulence. In this work, an FSO transmission system with high-speed transmission capability is proposed by deploying orthogonal frequency division multiplexing (OFDM) to mitigate channel fading effects. Further, we propose the hybridization of polarization division multiplexing (PDM) with CO-OFDM to improve the system capacity. We perform the bit error rate (BER) and optical signal to noise ratio (OSNR) comparative analysis of multi-level quadrature amplitude modulation (QAM) schemes, i.e., 4-QAM, 16-QAM, 32-QAM, and 64-QAM at 100, 120, 360, and 480 Gbps transmission rates, respectively. The obtained results reveal that the 4-QAM modulation scheme achieves the highest transmission range and the least OSNR requirement. In terms of spectral efficiency, 64-QAM shows the best performance. Also, the impact of different climate conditions on the system performance has been investigated. Through simulations, we demonstrate a successful transmission of 100 Gbps 4-QAM information at 15 km. Furthermore, we numerically investigated the increasing scintillation effect on the BER system performance. The proposed system not only reduces the channel fading but also improves the information rate and maximum transmission distance. The reported work can be considered for future FSO systems even in adverse climate conditions.

A long-haul 100 Gbps hybrid PDM/CO-OFDM FSO transmission system: Impact of climate conditions and atmospheric turbulence