Cavity solitons in passive bulk semiconductor microcavities. I. Microscopic model and modulational instabilities

We consider a broad-area vertical microresonator with an active layer constituted by bulk GaAs driven by an external coherent homogeneous electromagnetic field, and we adopt a microscopic model that describes the field and carrier dynamics in the quasi-equilibrium regime. The theory is developed within the free-carrier approximation, with some relevant effects, such as the Urbach tail and the bandgap renormalization, which are taken into account in a phenomenological way. We include in the model the description of paraxial diffraction and carrier diffusion. A detailed study of the instabilities, both modulational and plane wave, affecting the homogeneous stationary state of the output field is performed. In this way we address the numerical research of cavity solitons, which appear as self-organized light peaks embedded in a homogeneous background, as discussed in a companion paper [J. Opt. Sec. Am. B 16, 2095 (1999)]. Optimal conditions for cavity solitons' existence are found in extended regions of the parameter space. (C) 1999 Optical Society of America [S0740-3224(99)01011-5].