Significant enhancement of second-harmonic generation in SiNx resonant waveguide grating

Resonant waveguide gratings (RWG) consist of a surface waveguide and a surface grating that diffracts light both into and out of the waveguide mode for a particular angle of incidence. On resonance, the field diffracted out of the waveguide mode interferes with the directly transmitted and reflected fields in such a way that it is possible (at least theoretically) to obtain 100% reflection. Significantly, RWGs can also lead to strong local fields within the structure, which can enhance two-photon fluorescence or second-harmonic generation (SHG). Here, we report on SHG from an all-dielectric sub-wavelength RWG made of SiNχ that allows for a 1000x enhancement compared to a thin-film of the same material of comparable thickness and in optimum geometry.