Strongly interacting solitons confined to an optical resonator would offer unique capabilities for experiments in communication, computation, and sensing with light. Here we report on the discovery of soliton crystals in monolithic Kerr microresonators-spontaneously and collectively ordered ensembles of co-propagating solitons whose interactions discretize their allowed temporal separations. We unambiguously identify and characterize soliton crystals through analysis of their 'fingerprint' optical spectra, which arise from spectral interference between the solitons. We identify a rich space of soliton crystals exhibiting crystallographic defects, and time-domain measurements directly confirm our inference of their crystal structure. The crystallization we observe is explained by long-range soliton interactions mediated by resonator mode degeneracies, and we probe the qualitative difference between soliton crystals and a soliton liquid that forms in the absence of these interactions. Our work explores the rich physics of monolithic Kerr resonators in a new regime of dense soliton occupation and offers a way to greatly increase the efficiency of Kerr combs; further, the extreme degeneracy of the configuration space of soliton crystals suggests an implementation for a robust on-chip optical buffer.Optical solitons have recently found a new realization in frequency combs generated in passive, monolithic Kerrnonlinear resonators 1 (microcombs). These microcombs are a major step forward in frequency-comb technology 2 because they enable generation of combs in platforms having low size, weight, and power requirements. When a continuous-wave pump laser is coupled into a whispering-gallery mode of a high-Q Kerr resonator, broad optical spectra are generated through cascaded four-wave mixing. With appropriate power and laser-resonator frequency detuning, the resulting fields modelock to form circulating dissipative Kerr-cavity solitons [3][4][5][6][7][8][9][10] . These solitons are pulsed excitations atop a non-zero continuous wave background, and have robust deterministic properties that may be tailored through resonator design 11,12 and tuned in real-time through manipulation of the pump laser. Microcombs based on solitons extend the range of accessible comb repetition rates and provide a route towards chip-integrated self-referenced comb technology.Single solitons and ensembles of several co-propagating solitons have been reported in Kerr resonators constructed from a variety of crystalline and amorphous materials 3-7 , with repetition rates ranging from 22 GHz 6 to 1 THz 7 . Formally equivalent to monolithic Kerr resonators are lower repetition-rate fiber-loop resonators, where generation and control of soliton ensembles has recently been explored experimentally [13][14][15][16] . These experiments were preceded by theoretical studies of soliton interactions and ensembles of solitons in quasi-CW-pumped fiber-ring resonators [17][18][19] , where an analogy between soliton ensembles and the states of matter was introduc...

No abstract

No abstract

Ultralow-noise yet tunable lasers are a revolutionary tool in precision spectroscopy, displacement measurements at the standard quantum limit, and the development of advanced optical atomic clocks. Further applications include lidar, coherent communications, frequency synthesis, and precision sensors of strain, motion, and temperature. While all applications benefit from lower frequency noise, many also require a laser that is robust and compact. Here, we introduce a dual-microcavity laser that leverages one chipintegrable silica microresonator to generate tunable 1550 nm laser light via stimulated Brillouin scattering (SBS) and a second microresonator for frequency stabilization of the SBS light. This configuration reduces the fractional frequency noise to 7.8 × 10 −14 1∕ p Hz at 10 Hz offset, which is a new regime of noise performance for a microresonator-based laser. Our system also features terahertz tunability and the potential for chip-level integration. We demonstrate the utility of our dual-microcavity laser by performing spectral linewidth measurements with hertz-level resolution.