Resonant four-wave mixing microscopy on silicon-on-insulator based zero-contrast gratings

Abstract

In this paper, we report large area four-wave mixing microscopy studies on silicon-on-insulator based partially etched two-dimensional zero-contrast gratings. The zero-contrast gratings offer an additional degree of freedom for the design of spectral resonances by varying the etch depth of the grating structures. This is leveraged by designing signal resonance at 1580 nm, operating in the sub-wavelength, zeroth-order diffraction region and pump fixed at 1040 nm operating in the higher order diffraction region. The zero-contrast gratings are fabricated on standard 220 nm silicon-on-insulator substrates with etch depth chosen as 140 nm. The fabricated structures are characterized to measure the linear transmission and nonlinear four-wave mixing performance. Multi-spectral four-wave mixing images acquired across the grating structures for varying input signal wavelength show maximum enhancement of four-wave mixing signal at 1575 nm, with the on-grating four-wave mixing signal enhanced by ∼ 450 times when compared to the un-patterned film. Zero-contrast gratings present a promising platform for realizing sub-wavelength scale nanostructured surfaces for nonlinear wave-mixing applications using standard silicon-on-insulator substrates. Such structures can find potential applications in wavelength conversion across widely separated wavelength bands and as substrates for nonlinear frequency conversion.