Optical harmonic generation in amorphous silicon nitride microcavities

Second harmonic (SH) and third harmonic (TH) generation in amorphous silicon nitride microcavity are experimentally investigated. The transmitted SH and TH signals are measured in the 0.9-1.4 μm spectral range, showing enhanced nonlinear conversion efficiency corresponding to resonant wavelength and optical band edges. The efficiencies of the SH and TH generation processes are found to be enhanced by about two and one orders of magnitude, respectively, in comparison with the case of reference amorphous silicon nitride sample. The SH spectra can be reasonably interpreted as due to surface/interface harmonic generation, while the TH signal is related to bulk isotropic third-order polarization. The results obtained for the TH signal are discussed in terms of the linear optical properties of amorphous silicon nitride thin films.