Long-haul coherent communications using microresonator-based frequency combs

Microresonator-based frequency combs are strong contenders as light sources for wavelength-division multiplexing (WDM). Recent demonstrations have shown the potential of microresonator combs for replacing tens of WDM channels with a single laser-pumped device. These experiments relied on microresonators displaying anomalous dispersion. Devices operating in the normal dispersion offer the prospect of attaining high power conversion efficiency - an aspect that will be crucial in the future for enabling coherent communications with highly complex modulation formats or lighting several spatial channels in space-division multiplexing. Here we report the first experimental demonstration of coherent communications using normal dispersion microresonator combs. With polarization multiplexed (PM) quadrature phase-shift keying, we transmitted data over more than 6300 km in fiber. In a second experiment, we reached beyond 700 km with the more sensitive PM 16 quadrature amplitude modulation and an aggregate data rate close to one terabit per second. This represents the longest transmission ever achieved using an integrated comb source.