Second-harmonic-assisted four-wave mixing in chip-based microresonator frequency comb generation

Abstract

Simultaneous Kerr comb formation and second-harmonic generation with on-chip microresonators can greatly facilitate comb self-referencing for optical clocks and frequency metrology. Moreover, the presence of both second- and third-order nonlinearities results in complex cavity dynamics that is of high scientific interest but is still far from being well-understood. Here, we demonstrate that the interaction between the fundamental and the second-harmonic waves can provide an entirely new way of phase matching for four-wave mixing in optical microresonators, enabling the generation of optical frequency combs in the normal dispersion regime under conditions where comb creation is ordinarily prohibited. We derive new coupled time-domain mean-field equations and obtain simulation results showing good qualitative agreement with our experimental observations. Our findings provide a novel way of overcoming the dispersion limit for simultaneous Kerr comb formation and second-harmonic generation, which might prove to be especially important in the near-visible to visible range where several atomic transitions commonly used for the stabilization of optical clocks are located and where the large normal material dispersion is likely to dominate.

Soliton and quasi-soliton frequency combs due to second harmonic generation in microresonators

“…Using nonlinear effects other than Kerr nonlinearity for comb generation is an active research area. One can mention here examples of the comb generation due to cascaded Raman and Brillouin effects [3][4][5][6], polariton [7,8] and graphene nonlinearities [9], and quadratic, χ (2) , nonlinear effects [10][11][12][13][14][15][16][17][18][19][20][21][22]. The latter hold a particular promise.…”

Modeling of quasi-phase-matched cavity-enhanced second-harmonic generation

“…To further proceed, boundary conditions are explicitly included into the evolution equations. A similar approach has been already employed to generalize the Lugiato-Lefever model of a passive fiber cavity [32] or in micro resonators [33]. This method consists on unfolding the cavity and modelling it as a waveguide with periodic localized gain and losses.…”

Frequency comb generation in continuously pumped optical parametric oscillator

“…Similarly, as Kerr microresonators can only generate combs around the pump wavelength, the lack of mid-IR continuous wave lasers prevents that technology from being directly applied in the mid-IR region. While concurrent second-order up-conversions have been observed in Kerr microresonators with weak second-order nonlinearity [34][35][36], no down-converted comb has been observed so far.…”