Frequency Comb Generation in 300 nm Thick SiN Concentric-Racetrack-Resonators: Overcoming the Material Dispersion Limit

TL;DR

This paper demonstrates a novel concentric racetrack resonator in 300 nm thick silicon nitride that achieves anomalous dispersion suitable for integrated frequency combs, overcoming material dispersion limitations in standard semiconductor fabrication.

Contribution

Introduces a concentric racetrack resonator design that enables anomalous dispersion in thin silicon nitride films, compatible with standard semiconductor manufacturing processes.

Findings

High intrinsic Q of 1.5 million achieved

Anomalous dispersion over broad bandwidth demonstrated

Evidence of soliton-like pulse formation provided

Abstract

Kerr nonlinearity based frequency combs and solitons have been generated from on-chip optical microresonators with high quality factors and global or local anomalous dispersion. However, fabrication of such resonators usually requires materials and/or processes that are not standard in semiconductor manufacturing facilities. Moreover, in certain frequency regimes such as visible and ultra-violet, the large normal material dispersion makes it extremely difficult to achieve anomalous dispersion. Here we present a concentric racetrack-shaped resonator that achieves anomalous dispersion in a 300 nm thick silicon nitride film, suitable for semiconductor manufacturing but previously thought to result only in waveguides with high normal dispersion, a high intrinsic Q of 1.5 million, and a novel mode-selective coupling scheme that allows coherent combs to be generated. We also provide evidence suggestive of soliton-like pulse formation in the generated comb. Our method can achieve anomalous dispersion over moderately broad bandwidth for resonators at almost any wavelength while still maintaining material and process compatibility with high-volume semiconductor manufacturing.