Polarization state of quadratic spatial optical solitons - art. no. 066601

We derive governing equations that determine a full polarization state of t ransversely two-dimensional spatial solitons in a bulk anisotropic medium w ith the second-order nonlinearity. Based on nonlinear vectorial Maxwell's e quations and approximation of slowly varying envelopes, our approach descri bes also lowest-order nonparaxial effects, however the most important facto r governing radiation polarization is the medium anisotropy. This factor re sults in mixing of orthogonal components of electric field of quadratic sol iton that consists of coupled beams at the fundamental frequency and its se cond harmonics. For the case of weak anisotropy we determine the soliton po larization state by a perturbation method: it turns out that it is elliptic al and changing over the soliton transverse section. The approach allows ge neralization to the case of optical parametric oscillators.