Design of couplers based on cascaded second-order nonlinearity taking into account hybrid propagation

The optical behaviour of waveguides and couplers which exploit the cascaded second-order nonlinearity can be strongly influenced by the nature of the involved propagation modes. In this paper, the effects of the leaky nature of the generated second harmonic field (SH) are taken into account for a set of different cases. Symmetric and asymmetric coupling structures are investigated and compared. The coupled wave theory and the anisotropic complex mode propagation are the basic formalisms which allow the investigation of devices based on both guided and leaky propagation and suffering losses. The results, calculated by means of a home-made computer code, for those structures in which it is possible to neglect leaky nature of propagation modes, are compared with the literature data and an excellent agreement is found.