Quadratic Solitons in Singly Resonant Degenerate Optical Parametric Oscillators

By identifying the similarities between the coupled-wave equations and the parametrically driven nonlinear Schr\"odinger equation, we show the existence conditions of quadratic solitons in continuous-wave pumped singly resonant degenerate optical parametric oscillators (SRDOPOs). Compared to the previously explored doubly resonant DOPOs, quadratic solitons in SRDOPOs are advantageous in their robustness against perturbations induced by dispersion of the effective third-order nonlinearity and temporal walk-off between the signal and the pump. Terahertz comb bandwidth and femtosecond pulse duration are attainable in an example periodically poled Lithium niobate waveguide resonator in the short-wave infrared. The working principle can be extended to other material platforms, making it a competitive ultrashort pulse and broadband comb source architecture at the mid-infrared spectral range.