# Phase Modulation for Quadruplex Channels of Arbitrary Orthogonal Polarization States via Bilayer Metasurfaces

## TL;DR

This paper introduces a new method to control light's polarization states using bilayer metasurfaces, enabling advanced optical applications.

## Contribution

The novel strategy allows four-channel phase modulation and energy distribution for arbitrary orthogonal polarization states using bilayer metasurfaces.

## Key findings

- Wavefront modulations for quadruplex polarization channels are demonstrated using bilayer metasurfaces.
- Flexible energy distribution is achieved by adjusting polarization conversion efficiency.
- Applications include orbital angular momentum manipulation and Bessel beam generation.

## Abstract

Optical metasurfaces are widely studied due to their unprecedented wavefront modulation capabilities for multiple polarization channels. Current studies predominantly focus on complete polarization conversion. Recent progress indicates that the phases of quadruplex polarization channels can be independently modulated under incomplete polarization conversion conditions. However, these four‐channel phase modulation operations are limited to circular or linear polarization states and neglect amplitude modulation. Here, a strategy is proposed to achieve four‐channel phase modulation and flexible energy distribution of arbitrary orthogonal polarization states under incomplete polarization conversion conditions. Wavefront modulations for quadruplex channels of arbitrary orthogonal polarization states (circular, linear, elliptical, and first‐order cylindrically vectorial), such as orbital angular momentum manipulation, Bessel beam generation, deflection, and holography, are numerically demonstrated based on this strategy. Furthermore, the energy distribution of the quadruplex polarization channels is achieved by varying the polarization conversion efficiency. These operations are implemented through all‐dielectric free‐standing bilayer metasurfaces. The proposed design strategy extends the application of metasurfaces in multichannel optical field modulation.

This work demonstrates a strategy for four‐channel phase modulation and flexible energy distribution of arbitrary orthogonal states of polarization under incomplete polarization conversion conditions. Such a strategy can be implemented through an all‐dielectric free‐standing bilayer metasurface configuration and can be used for multichannel optical field manipulation.