Quadratic frequency comb based on phase-modulated cw-driven optical parametric oscillator with intracavity dispersion control

Abstract: We report a novel configuration of bulk $\chi^{(2)}$ optical parametric oscillator (OPO) capable of delivering coherent broadband phase-locked spectrum when driven by a continuous-wave (cw) pump laser. By deploying an electro-optic modulator (EOM) internal to a degenerate cw OPO based on MgO:sPPLT or MgO:PPLN and implementing intracavity dispersion control, we show that output spectra extending over 9 nm (119 nm) with well-defined phase coherence can be generated. Pumping the cw OPO at 532~nm (1550~nm) for degenerate operation in the normal (anomalous) dispersion regime at 1064~nm (3100~nm), and using the coupled-wave equations to simulate the OPO in the presence of intracavity dispersion compensation, we demonstrate that this device offers a new alternative for $\chi^{(2)}$-based frequency comb generation. We also show that in the time domain the output of such a device corresponds to femtosecond quadratic solitons in both dispersion regimes. The described concept is generic, paving the way for the realization of a new class of coherent broadband frequency comb sources in different spectral regions based on $\chi^{(2)}$ OPOs pumped by cw lasers.