Résumé : We experimentally demonstrate that optical frequency combs can be generated in a cw-pumped, nearly degenerate, doubly resonant optical parametric oscillator (OPO). Moreover, we present a time-domain theoretical model of the OPO and derive a non-instantaneous mean field dynamic equation for the parametric field. Numerical simulations of the mean field equation are in good agreement with the observed comb patterns. © OSA 2017.