Metacoatings for wavelength scale, high NA plano-concave focusing lenses

TL;DR

This paper introduces silicon plano-concave lenses with gradient-index plasmonic metacoatings that enable ultrawide aperture focusing in a compact region, significantly improving optical resolution for applications like trapping and detection.

Contribution

It presents a novel design of wavelength-scale, high-NA plano-concave lenses with coupled plasmonic metacoatings for enhanced focusing performance.

Findings

Achieved ultrawide aperture focusing within ~20 λ² region.

Enhanced wavefront curvature leads to improved resolution.

Formation of a light tongue near the concave opening.

Abstract

We design plano-concave silicon lenses with coupled gradient-index plasmonic metacoatings for ultrawide apertured focusing utilizing a reduced region of $\sim 20 \lambda^2$. The anomalous refraction induced in the planar input side of the lens and in the boundary of the wavelength-scale focal region boosts the curvature of the emerging wavefront, thus significantly enhancing the resolution of the tightly-focused optical wave. The formation of a light tongue with dimensions approaching those of the concave opening is here evidenced. This scheme is expected to have potential applications in optical trapping and detection.