Abstract
Optical frequency combs, a revolutionary light source characterized by discrete and equally spaced frequencies, are usually regarded as a cornerstone for advanced frequency metrology, precision spectroscopy, high-speed communication, distance ranging, molecule detection, and many others. Due to the rapid development of micro/nanofabrication technology, breakthroughs in the quality factor of microresonators enable ultrahigh energy buildup inside cavities, which gives birth to microcavity-based frequency combs. In particular, the full coherent spectrum of the soliton microcomb (SMC) provides a route to low-noise ultrashort pulses with a repetition rate over two orders of magnitude higher than that of traditional mode-locking approaches. This enables lower power consumption and cost for a wide range of applications. This review summarizes recent achievements in SMCs, including the basic theory and physical model, as well as experimental techniques for single-soliton generation and various extraordinary soliton states (soliton crystals, Stokes solitons, breathers, molecules, cavity solitons, and dark solitons), with a perspective on their potential applications and remaining challenges.
Highlights
Optical microcavities, which emerged from the rapid development of modern micro/nanofabrication technologies, have grown to be revolutionary devices that light the way toward several fantastic applications, including advanced light sources, ultrafast optical signal processing, and ultrasensitive sensors, benefitting from their unprecedented small size and high buildup of energy inside the resonators.[1]
In the case of microcavities made of materials with inversion symmetry, the elemental nonlinear interaction is third-order nonlinearity, which gives rise to the parametric process of four-wave mixing (FWM)
Compared with traditional OFCs built on mode-locked solid-state or fiber lasers, microcomb is considered a new type of coherent light source that shows unique and promising advantages of lower power consumption as well as whole system integratability
Summary
Optical microcavities, which emerged from the rapid development of modern micro/nanofabrication technologies, have grown to be revolutionary devices that light the way toward several fantastic applications, including advanced light sources, ultrafast optical signal processing, and ultrasensitive sensors, benefitting from their unprecedented small size and high buildup of energy inside the resonators.[1]. Raman self-frequency shift) that are closely related to the characteristics of microresonators have been disclosed.[12,24,25,26,27] All of these achievements suggest that SMCs can establish an interface between soliton physics and integrated photonics as well as materials science. SMC generation in the visible,[31,33] near-,10,13,15,30,34,35 and midinfrared[36] regions have all been achieved, covering a wavelength range of down to ∼750 nm[31] and up to ∼4300 nm.[36] Benefitting from the full coherent feature across the whole spectral coverage[10,11,12,37] the advent of SMCs has promoted research in various applications, such as dual-comb spectroscopy (DCS),[38] terabit coherent optical communications,[39] photonic-integrated frequency synthesizers,[40] ultrafast distance measurements,[41] and calibration of astrophysical spectrometers for exoplanet searching.[42] Beyond these developed applications, SMCs are relevant to a large variety of physical systems that could provide ideal testbeds for fundamental theory of nonlinear wave dynamics research.[43,44].
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