Spatial quadratic solitons guided by narrow layers of a nonlinear material

Received February 7, 2011; revised April 16, 2011; accepted April 19, 2011; posted April 19, 2011 (Doc. ID 142374); published May 19, 2011 We report analytical solutions for spatial solitons supported by layers of a quadratically nonlinear (χð2Þ) material embedded into a linear planar waveguide. A full set of symmetric, asymmetric, and antisymmetric modes pinned to a symmetric pair of the nonlinear layers is obtained. The solutions describe a bifurcation of the subcritical type, which accounts for the transition from the symmetric to asymmetric modes. The antisymmetric states (which do not undergo the bifurcation) are completely stable (the stability of the solitons pinned to the embedded layers is tested by means of numerical simulations). Exact solutions are also found for nonlinear layers embedded into a nonlinear waveguide, including the case when the uniform and localized χð2Þ nonlinearities have opposite signs (competing nonlinearities). For the layers embedded into the nonlinear medium, stability properties are explained by comparison to the respective cascading limit. © 2011 Optical Society of America OCIS codes: 190.5530, 190.4350, 190.4410.