Microresonator frequency combs (microcombs) are a promising technology for generating frequency carriers for wavelength division multiplexing (WDM) systems. Multi-terabit per second WDM coherent transmitters have recently been demonstrated using both dissipative Kerr solitons and mode-locked dark pulses in optical microresonators. These experiments have focused on microcombs designed to cover a large portion of the erbium-doped fiber window. However, the question of optimum bandwidth for microcombs in WDM systems has not been addressed. Here we show that segmenting the bandwidth into smaller microcomb-driven superchannels results in an improvement of power per line. Through numerical simulations we establish a quantitative comparison between dark-pulse and soliton microcombs in WDM systems, including aspects such as conversion efficiency, tolerance to intrinsic cavity loss, and group velocity dispersion engineering. We show that the improvement of minimum line power scales linearly with the number of superchannels for both types of microcombs. This work provides useful guidelines for the design of multi-terabit per second microcomb-based superchannel systems
