SOLITARY WAVES IN QUADRATICALLY NONLINEAR RESONATORS

We identify two-dimensional stable and unstable bright solitary waves or localized structures in a planar resonator with a quadratically non linear medium driven by a field at the fundamental frequency only. The se waves are extremely localized while the nonlocal interaction betwee n the fundamental and second harmonics prevents a collapse. To a certa in extent they can be regarded as residuals of coexisting hexagon patt erns.