Soliton pulse pairs at multiple colors in normal dispersion microresonators

Abstract

Soliton microcombs [1] are helping to advance the miniaturization of a range of comb systems [2]. These combs mode lock through the formation of short temporal pulses in anomalous dispersion resonators. Here, a new microcomb is demonstrated that mode locks through the formation of pulse pairs in normal-dispersion coupled-ring resonators. Unlike conventional microcombs, pulses in this system cannot exist alone, and instead must phase lock in pairs to form a bright soliton comb. Also, the pulses can form at recurring spectral windows and the pulses in each pair feature different optical spectra. This pairwise mode-locking modality extends to higher dimensions and we demonstrate 3-ring systems in which 3 pulses mode lock through alternating pairwise pulse coupling. The results are demonstrated using the new CMOS-foundry platform that has not previously produced bright solitons on account of its inherent normal dispersion [3]. The ability to generate multi-color pulse pairs over multiple rings is an important new feature for microcombs. It can extend the concept of all-optical soliton buffers and memories [4,5] to multiple storage rings that multiplex pulses with respect to soliton color and that are spatially addressable. The results also suggest a new platform for the study of quantum combs [6-8] and topological photonics [9][10][11].

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.…”