Performance analysis of dual-polarization PAM-4 modulated hybrid SMF–FSO link under wet and dry snow atmospheric conditions

A 100 Gbps PAM-4 (DP-PAM-4) modulated single-mode fiber–free space optics (SMF–FSO) link with wet and dry snow is investigated in this study. The system is simulated in OptiSystem for SMF length 10 km, 15 km, and 20 km for different FSO range. The performance is evaluated using the logarithm of bit error rate (Log(BER)), error vector magnitude (EVM), and received optical power (ROP). The maximum evaluated FSO reach is 2,050 m under the wet snow attenuation of 8.24 dB/km, while the best log(BER) and EVM are obtained at 1,250 m with 10 km of SMF. Under dry snow attenuation of 24.85 dB/km, the corresponding range decreases to 875 m, with the best log(BER) of −3.010 and EVM of 17.25 % at 575 m using 10 km of SMF. An increase in SMF length from 10 km to 20 km results in a 5–6 percentage point loss in EVM due to intersymbol interference caused by dispersion. In most of the evaluated FSO ranges, the 20 km configuration is above the stated 32.5 % EVM threshold. The eye diagrams show degradation of the signal as the fiber length and the distance between the FSO increases. The results provide design guidance for the deployment of SMF–FSO in snowy environments and are applicable to optical link budget design.