Enhanced effective nonlinearities in silicon nitride free-standing nanopatterned membranes

Silicon nitride (SiN) represents a promising complementary metal-oxide-semiconductor material for on-chip nanophotonics applications due to its unexpected linear and nonlinear optical properties. Here, we experimentally and numerically investigate the linear and nonlinear response of SiN free-standing nanostructured thin-film membranes. Compared to the unpatterned platform, the design of a square-lattice patterning gives rise to a nonlocal resonant mode that enhances the effective third-order optical nonlinearity by a factor of 3.4-5 at the resonance wavelength, as determined from Z-scan experiments. Finite-element simulations clarify that the magnitude of the lattice-induced frequency dispersion of the Kerr coefficient also depends on the spectral and geometrical properties of the interacting light excitation. Our results propose patterned SiN nanomembranes as a promising nanophotonics platform for enhanced nonlinear frequency conversion processes.