General lossless polarization and phase transformation using bilayer metasurfaces

TL;DR

This paper introduces a systematic design method for bilayer metasurfaces that achieve arbitrary lossless polarization and phase transformations, surpassing the limitations of single-layer metasurfaces.

Contribution

It demonstrates that two cascaded birefringent metasurface layers enable arbitrary unitary polarization and phase transformations, including chiral states, with high efficiency.

Findings

Design method for bilayer metasurfaces with arbitrary transformations

Implementation of a bifocal metalens with complex polarization control

High-efficiency, lossless polarization and phase manipulation

Abstract

Metasurface optical elements enable wavefront control and polarization manipulation with subwavelength resolution. Metasurfaces made of linearly birefringent meta-atoms such as rectangular nano-posts are commonly used to control phase and polarization, but a single layer of these meta-atoms cannot implement transformations with elliptically polarized or circularly polarized eigenstates (i.e., chiral transformations). Here, it is shown that two cascaded metasurface layers comprising linearly birefringent meta-atoms provide sufficiently many degrees of freedom to implement arbitrary unitary phase and polarization transformations. A systematic design method for such metastructures is described and used to design a bifocal metalens that cannot be implemented by a single layer of birefringent meta-atoms. The presented design and implementation techniques introduce a systematic approach for realizing the most general form of lossless polarization and phase transformations using metasurfaces with high efficiency.