Low Contrast Dielectric Metasurface Optics

TL;DR

This paper demonstrates that low contrast dielectric materials like silicon nitride can be used to create efficient, high-resolution metasurface optical elements, challenging the belief that high refractive index materials are necessary.

Contribution

It introduces design principles for low contrast metasurfaces and validates them through fabrication and experimental characterization of silicon nitride lenses and vortex beam generators.

Findings

Achieved sub-micron beam spots with high numerical aperture (~0.75).

Observed 90% transmission and 40% focusing efficiency in visible light.

Proved low contrast materials can be effective for metasurface optics.

Abstract

The miniaturization of current image sensors is largely limited by the volume of the optical elements. Using a sub-wavelength patterned quasi-periodic structure, also known as a metasurface, one can build planar optical elements based on the principle of diffraction. However, it was believed that high refractive index materials are required for metasurface optics. Here, we show that one can employ the design principles of a metasurface even with low contrast materials, such as silicon nitride. We validate our theory by fabricating and experimentally characterizing several silicon nitride based lenses and vortex beam generators . The fabricated lenses achieved beam spots of less than 1 {\mu}m with numerical apertures as high as ~ 0.75. A transmission efficiency of 90% and focusing efficiency of 40% in the visible regime was observed. Our results pave the way towards building low-loss metasurface based optical elements at visible frequencies using low contrast materials.