Engineered zero-dispersion microcombs using CMOS-ready photonics

Kavli Affiliate: Kerry Vahala

| First 5 Authors: Qing-Xin Ji, Warren Jin, Lue Wu, Yan Yu, Zhiquan Yuan

| Summary:

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.

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