Engineered zero-dispersion microcombs using CMOS-ready photonics

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 toward scalable production. However, the chromatic dispersion of CMOS devices is large and impairs the generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a coupled-ring resonator configuration. Operating in the turnkey self-injection locking mode, the resonator is integrated in a hybrid manner 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 integrated hybrid system could be used in coherent communications or for ultrastable microwave signal generation by two-point optical frequency division.

Multimodality integrated microresonators using the Moiré speedup effect

“…Further device details are provided in the supplementary materials, but briefly, the intrinsic Q factor is 95 million, the average FSR of the two rings is 19.95 GHz, and their FSR difference dFSR is 100 MHz, so that R ≈ FSR/dFSR = 200. The rings couple along a straight section to form hybrid-mode frequency bands (7,8) whose dispersion spectra are modulated by the Moiré effect. By applying voltage to one of the ring heaters, the frequency ruling of the corresponding resonator is shifted, thereby inducing a much larger spectral shift of the dispersion through the speedup effect.…”

“…We used four different distributedfeedback (DFB) semiconductor lasers operating at four different wavelengths. At each pumping wavelength, tuning of the resonator dispersion allows operation in either the bright or dark mode (7,8). A measurement of realtime switching between a bright-soliton and dark-pulse microcomb state is presented in fig.…”

“…Its analog in optical resonators overlays two frequency scales with different divisions set by the free spectral range, FSR, of two resonators. The coupling of such resonators is mediated by the frequency Vernier and creates useful tuning effects that benefit optical add-drop filters (1), semiconductor lasers (2), and frequency microcombs (3)(4)(5)(6)(7)(8). Verniers feature a larger scale periodicity that is associated with the Moiré pattern (9) that they form when overlaid.…”

Quintic Dispersion Soliton Frequency Combs in a Microresonator

“…Note added: we would like to draw the reader's attention to two related recent works [46,47] that were published during the review process.…”

Unexpected phase-locked Brillouin Kerr Frequency comb in fiber Fabry Perot resonators

“…Most of Kerr comb generation are based on cavity solitons generation in anomalous group velocity dispersion (GVD) resonators, resulting in a stable soliton recirculating in the resonator and a broad homogeneous OFC at the cavity output [14,16]. However, normal GVD resonators are increasingly utilized for OFCs generation, in particular because of their high conversion efficiency between the pump and the generated comb lines [8,[17][18][19][20]. As the upper branch of a normally dispersive cavity does not exhibit modulation instability, various excitation techniques had to be identified to trigger OFCs in this regime, notably through mode-crossing effect [17,18], Brillouin effect [21], dual-pumping [22], coupled-cavity [18,19,23], modulated pump [20] or pulsed pumping scheme [24][25][26][27][28].…”