Stable self-guided propagation of two optical harmonics coupled by a microwave or a terahertz wave

We propose a new scheme for self-trapping of (2+1)-dimensional optical beams: parametric interaction between self-guided waves of optical and microwave (or terahertz) frequencies, which relies on the combination of optical rectification and the electro-optic effect in a bulk noncentrosymmetric medium. We show that, in spite of strong domination of quasi-cubic terms, quadratic nonlinearity provides an effective stabilization mechanism to prevent collapse in a large range of parameters where three-wave solitons exist.