Self-induced thermal effects and modal competition in continuous-wave optical parametric oscillators

We present a model of quasi-phase-matched continuous-wave optical parametric oscillators that accounts for self-induced heating of the photorefractive crystal and modal interaction through pump depletion. The model allows the temperature and therefore the refractive index of the nonlinear medium to vary in the radial and longitudinal dimensions as a result of local absorption of the optical power. We consider the effect of this nonuniform index on single-mode and multimode operation. For a single signal–idler pair we observe thermal lensing, bulk tuning, and modal distortion. For multiple pairs of signal and idler we demonstrate and discuss other phenomena, including spatially dependent modal competition. © 2002 Optical Society of America OCIS codes: 190.4870, 190.4970, 190.2620, 190.4420.