We present a theoretical and experimental study of parametric generation in a guided wave quasi-phase-matched configuration, A numerical model taking into account inverted domain shape, electrooptic and photorefractive effects, as well as waveguide profiles allo rvs calculation of the observed phase matching curves, The observed parametric fluorescence efficiencies can be explained by assuming a slight reduction of nonlinear coefficient and/or a partial degradation of the nonlinear grating. Optimization of the grating depth profile would permit room temperature parametric oscillation using pump wavelengths and powers attainable with diode lasers.