Extending chip-based Kerr-comb to visible spectrum by dispersive wave engineering

Abstract

Anomalous group velocity dispersion is a key parameter for generating bright solitons, and thus wideband Kerr frequency combs. Extension of frequency combs to visible wavelength in conventional photonic materials and structures has been a major challenge due to strong normal material dispersion at the relevant frequencies. Extension of frequency combs toward the normal dispersion region is possible via dispersive waves through soliton-induced Cherenkov radiation. However, this potentially powerful technique has not been used for extending frequency combs to the visible spectrum. In this paper, we demonstrate a new microresonator structure formed by an over-etched silicon nitride waveguide that enables the use of soliton-induced Cherenkov radiation to extend the bandwidth of the Kerr-combs. Furthermore, we show that by careful dispersion engineering in a coupled microring resonator structure we can optimize the properties (e.g., wavelength, and amplitude) of the generated dispersive wave to further extend the Kerr frequency combs to the visible spectrum while increasing the total Kerr-comb bandwidth as well.

Wideband bright-soliton frequency-comb generation at optical telecommunication wavelength in a thin silicon nitride film

“…3(a), which represents induced anomalous dispersion in several regions (including the pumping wavelength) separated by regions with the normal dispersion. These cascaded anomalous dispersion regions extend the Kerr-comb bandwidth 13.…”

“…We numerically study the dispersion of the resonant modes in the coupled-resonator structure with optimized coupling for both cases to demonstrate the applicability of our approach for bright-soliton Kerr-comb generation. Coupled-mode-theory (CMT) is used to find the resonant modes of the cold coupledresonator structure, 13 while the exact dispersion of the waveguiding structure (bent to form the resonators) is studied using the FEM implemented in the COMSOL multiphysics environment. In addition, Kerr-comb generation is numerically studied by solving the generalized Lugiato-Lefever equation (LLE), with dispersion parameters of the cold odd-resonant modes, using the split-step Fourier method.…”

Advanced dispersion engineering of a III-nitride micro-resonator for a blue frequency comb

“…‡ Cavity losses include (small) material absorption, radiation loss that is exacerbated by the bending of the guide, and (small) transmittance of the coupling port. An overall damping coeficient α does not appear explicitly in (8), however, since it is aggregated with other terms during the normalization process. the anti-Stokes lines in crystalline AlGaN are separated by about 18 THz from the pump frequency, with a linewidth of about 100 GHz [26].…”

“…There has been significant progress on both theoretical and experimental fronts, to the point where we now have fully developed spectro-and spatio-temporal models [6,7] of the nonlinear dynamical Kerr-comb generation process inside a micro-resonator, advanced dispersion engineering approaches [8][9][10][11] for micro-resonator design optimization, as well as fabrication processes for Si 3 N 4 -based structures [12][13][14], allowing the manufacture of near-IR micro-resonators with very high quality factors (Q) in a variety of material platforms (Si, SiO 2 , Si 3 N 4 , SiC, diamond, AlN, Al-GaAs, GaP, MgF 2 ). These advances have enabled the laboratory demonstrations of frequency-bin entangled photon sources and Doppler-cooling of atoms/ions [15,16], among others.…”

Robust cavity soliton formation with hybrid dispersion

“…As cascaded parametric processes, Kerr combs are generated with careful dispersion engineering. It has been studied in either anomalous or normal dispersion regime [4][5][6][7][8][9][10][11], related with bright or dark solitons. In analogue to a soliton formed in a waveguide or fiber [12], higher-order dispersion's influence on soliton formation has been studied recently [13][14][15][16][17][18].…”