Fig. 4.

Dark-pulse comb optimization for modern communication formats. a Simulation results showing the minimum comb-line powers as the waveguide’s group velocity dispersion coefficient, β₂, and the ring waveguide coupling constant, θ, are varied. The comb spacing is fixed at 100 GHz. The peak value marked with X at −10 dBm is achieved for β₂ = 350 ps²/km, θ = 0.011, and a detuning of δ₀ = 0.0445, yielding a comb with above 50% power-conversion efficiency and a flattened net conversion efficiency of 4.4%. b Optical spectrum of the optimized dark-pulse comb with line powers in the C band between 51 dB and 71 dB above the quantum noise limit at 0.1-nm resolution. c Theoretical OSNR requirements at the receiver side for a variety of modern communication formats and symbol rates, assuming additive white Gaussian noise and Gray-level coding⁶¹. For a single-polarized signal, the limits will be the same assuming that the noise is only measured in that polarization. We note that a doubling in the symbol rate or modulation format results in roughly a 3-dB increase in the OSNR requirement