We demonstrate optical frequency comb generation in a continuously pumped optical parametric oscillator, in the parametric region around half of the pump frequency. We also model the dynamics of such quadratic combs using a single time-domain mean-field equation, and obtain simulation results that are in good agreement with experimentally observed spectra. Moreover, we numerically investigate the coherence properties of simulated combs, showing the existence of correlated and phase-locked combs. Our work could pave the way for a new class of frequency comb sources, which may enable straightforward access to new spectral regions and stimulate novel applications of frequency combs.
We discuss recent advances in the modelling of optical frequency comb generation in quadratic and cubic microresonators.
Different time domain models are presented and compared, and their solutions are analysed by
Optical frequency combs currently represent enabling components in a wide number of fast-growing research fields, from frequency metrology to precision spectroscopy, from synchronization of telecommunication systems to environmental and biomedical spectrometry. As recently demonstrated, quadratic nonlinear media are a promising platform for optical frequency combs generation, through the onset of an internally pumped optical parametric oscillator in cavity enhanced second-harmonic generation systems. We present here a proposal for quadratic frequency comb generation in AlGaAs waveguide resonators. Based on the crystal symmetry properties of the AlGaAs material, quasi-phase matching can be realized in curved geometries (directional quasi-phase matching), thus ensuring efficient optical frequency conversion. We propose a novel design of AlGaAs waveguide resonators with strongly reduced total losses, compatible with long-path, high-quality resonators. By means of a numerical study, we predict efficient frequency comb generation with threshold powers in the microwatt range, paving the way for the full integration of frequency comb synthesizers in photonic circuits.
Various aspects of the nonlinear dynamics of Kerr frequency comb generation in optical microresonators are considered. It is shown that the comb generation process can, for the case of a single continuous wave pump, be given a simple interpretation in terms of modulational instability and that the essential dynamics can be captured using a three wave mode truncation for the pump mode and the dominant sideband pair. This idea is also extended using a four wave model to analyze an alternative dual pump configuration, for which comb generation may occur without a pump intensity threshold in both the normal and the anomalous dispersion regime.