Fiber-optic communications with microresonator frequency combs

Doctoral thesis, 2018

Modern data communication links target ever-higher information throughput. To utilize the available bandwidth in a single strand of fiber, optical communication links often require a large number of lasers, each operating at a different wavelength. A microresonator frequency comb is a chip-scale multi-wavelength laser source whose spectrum consists of multiple evenly spaced lines. As the line spacing of a microresonator comb is on the order of several tens of GHz, it provides a promising light source candidate for implementing an integrated multi-wavelength transceiver. The interest for using microresonator combs in communications applications has therefore increased greatly in the last five years. The application-related developments have been complemented with an increased exploration and understanding of the operating principles behind these devices.

This thesis studies microresonator frequency combs in both long-haul and high data-rate (multi-terabit per second) fiber communications systems. The results specifically include the longest demonstrated communications link with a microresonator light source as well as the highest order modulation format demonstration using any integrated comb source. The used microresonators are based on a high-Q silicon nitride platform provided by our collaborators at Purdue University. Part of the results are enabled by the high line powers resulting from a recently demonstrated novel comb state. This state bears similarities with dark solitons in fibers in that it corresponds to a train of dark pulses circulating inside the microresonator cavity. Overall, the results in this thesis provide a promising pathway towards enabling a future chip-scale multi-wavelength coherent transmitter.