Curved Gratings as Plasmonic Lenses for Linearly Polarised Light

TL;DR

This paper demonstrates how curved gratings can efficiently focus linearly polarized light into surface plasmons, with adjustable focusing properties and enhanced coupling using asymmetric configurations, advancing plasmonic lens technology.

Contribution

It introduces curved gratings as plasmonic lenses for linearly polarized light, showing their focusing capabilities and the benefits of asymmetric designs for improved performance.

Findings

Increasing sector angle reduces surface plasmon spot size.

Asymmetric gratings achieve higher intensity and smaller depth of focus.

Experimental results confirm theoretical and simulation predictions.

Abstract

The ability of curved gratings as sectors of concentric circular gratings to couple linearly polarized light into focused surface plasmons is investigated by theory, simulation and experiment. Curved gratings, as sectors of concentric circular gratings with four different sector angles, are etched into a 30-nm thick gold layer on a glass coverslip and used to couple linearly-polarised free space light at nm into surface plasmons. The experimental and simulation results show that increasing the sector angle of the curved gratings decreases the lateral spotsize of the excited surface plasmons, resulting in focussing of surface plasmons which is analogous to the behaviour of classical optical lenses. We also show that two faced curved gratings, with their groove radius mismatched by half of the plasmon wavelength (asymmetric configuration), can couple linearly-polarised light into a single focal spot of concentrated surface plasmons with smaller depth of focus and higher intensity in comparison to single-sided curved gratings. The major advantage of these structures is the coupling of linearly-polarised light into focused surface plasmons with access to and control of the plasmon focal spot, which facilitates potential applications in sensing, detection and nonlinear plasmonics.