Engineered zero-dispersion microcombs using CMOS-ready photonics

TL;DR

This paper demonstrates the development of CMOS-compatible microresonators with reduced GVD using a couple-ring configuration, enabling broadband, high-efficiency microcombs with stabilized repetition rates for advanced photonic applications.

Contribution

It introduces a novel couple-ring resonator design that reduces GVD in CMOS photonics, producing broadband microcombs with integrated stabilization capabilities.

Findings

Achieved 9.9 nm bandwidth microcombs with 62 lines at 1560 nm

Demonstrated near-zero GVD behaviors including soliton molecules and switching waves

Enabled electrical tuning and stabilization of the comb repetition rate

Abstract

Normal group velocity dispersion (GVD) microcombs offer high comb line power and high pumping efficiency compared to bright pulse microcombs. The recent demonstration of normal GVD microcombs using CMOS-foundry-produced microresonators is an important step towards scalable production. However, the chromatic dispersion of CMOS devices is large and impairs generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a couple-ring resonator configuration. Operating in the turnkey self-injection-locking mode, the resonator is hybridly integrated with a semiconductor laser pump to produce high-power-efficiency combs spanning a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb lines. Fast, linear optical sampling of the comb waveform is used to observe the rich set of near-zero GVD comb behaviors, including soliton molecules, switching waves (platicons) and their hybrids. Tuning of the 20 GHz repetition rate by electrical actuation enables servo locking to a microwave reference, which simultaneously stabilizes the comb repetition rate, offset frequency and temporal waveform. This hybridly integrated system could be used in coherent communications or for ultra-stable microwave signal generation by two-point optical frequency division.