Impact of impulse profile on the soliton microcombs for high-capacity FSO-WDM-PoLSK link

Improving the reliability and spectral efficiency of free-space optical (FSO) systems remains a major challenge under degraded channel conditions. Solitons represent a promising solution thanks to their ability to maintain shape through a balance between dispersion and nonlinearity. This work analyzes the impact of input pulse shaping on soliton stability in a WDM-based FSO link operating in subtropical conditions (Côte d’Ivoire). Four pulse profiles, Gaussian, super-Gaussian, Lorentzian, and hyperbolic secant are evaluated in terms of energy efficiency, bit error rate (BER), outage probability, spectral efficiency, and transmission distance. The system employs polarization shift keying (PolSK), 35 WDM channels spaced by 1 nm, and a gamma–gamma turbulence model. Results demonstrate the superiority of the Sech profile, which meets the equilibrium conditions of dissipative Kerr solitons. It achieves a reduced FWHM (∼0.105 ns), sub-picosecond jitter (<1 ps), enhanced PolSK stability, and lower power consumption. Sech pulses reach BER = 10 −6 at 16 dB SNR, sustain a maximum capacity of 5 bits/sym (175 Gbit/s over 35 channels), and extend transmission distance up to ∼25 km at 15 dB SNR, a 77 % gain over Gaussian and fivefold over super-Gaussian pulses. These findings highlight the critical role of pulse shaping in resilient, high-capacity FSO systems.