Gap-surface plasmon metasurfaces for linear-polarization conversion, focusing, and beam splitting

Abstract

Gap-surface plasmon (GSP) metasurfaces have attracted progressively increasing attention due to their planar configurations, ease of fabrication, and unprecedented capabilities in manipulating the reflected fields that enable integrating diverse bulk-optic-based optical components into a single ultrathin flat element. In this work, we design and experimentally demonstrate multifunctional metalenses that perform simultaneous linear-polarization conversion, focusing, and beam splitting, thereby reproducing the combined functionalities of conventional half-wave plates, parabolic reflectors, and beam splitters. The fabricated single-focal metalens incorporates properly configured distinct half-wave-plate-like GSP meta-atoms and exhibits good performance under linearly polarized incidence in terms of orthogonal linear-polarization conversion ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mo form="prefix">&gt;</mml:mo> <mml:mn>75</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> ) and focusing (overall <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mtext>efficiency</mml:mtext> <mml:mo>&gt;</mml:mo> <mml:mn>22</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> ) in the wavelength spectrum ranging from 800 to 950 nm. To further extend the combined functionalities, we demonstrate a dual-focal metalens that splits and focuses a linearly polarized incident beam into two focal spots while maintaining the capability of orthogonal linear-polarization conversion. Furthermore, the power distribution between two split beams can readily be controlled by judiciously positioning the incident beam. The demonstrated multifunctional GSP-based metalenses mimic the combined functionalities of a sequence of discrete bulk optical components, thereby eliminating the need for their mutual alignment and opening new perspectives in the development of ultracompact and integrated photonic devices.