Impact of microresonator geometry on FSO link performance in Málaga-modelled atmospheric turbulence

Free-space optical (FSO) communication offers high-capacity, license-free transmission but remains sensitive to atmospheric attenuation, turbulence-induced scintillation, finite receiver aperture, and pointing errors. Dissipative Kerr-soliton microcombs generated in integrated Si3N4 microresonators provide mutually coherent WDM carriers whose spacing and number depend directly on resonator geometry. This work develops a device-to-link framework connecting the generator-ring radius to the free spectral range (FSR), loaded quality factor, resonance linewidth, relative intensity noise, usable carrier count, receiver SNR, and aggregate FSO throughput. The radius is varied from 50 to 550 µm, reducing the FSR from approximately 482 to 43.8 GHz and increasing the number of C-band comb lines from 9 to 99. The FSO channel combines deterministic atmospheric attenuation, Málaga-M turbulence, Gaussian-beam pointing loss, finite-aperture collection, photodetector noise, and source RIN. Rytov variance is used only as an indicator of turbulence strength, while Málaga parameters are specified independently. Under a fixed total comb-power budget, increasing the radius increases carrier density but reduces the power available per line and makes WSS isolation more demanding. For moderate turbulence, the throughput-maximizing radius is approximately 350–450 µm at 1–2 km, shifts toward 250–150 µm at intermediate distances, and approaches 50 µm for the longest investigated ranges. WSS crosstalk increases from about −37 to −6 dB as the radius increases from 50 to 550 µm. These results show that the preferred microresonator geometry is strongly dependent on propagation and system operating conditions.