Chiral bilayer metasurfaces for fully phase-decoupled four-channel vortex light generation and holographic imaging

The multi-channel optical field manipulation capability of metasurfaces gives them great potential for application in system miniaturization and integrated optics. Recently, various methods have been proposed to increase the number of controllable circularly polarized (CP) functional channels to enhance the multifunctional integration capability of metasurfaces. However, these methods often suffer from non-uniform amplitude responses, incomplete decoupling, and excessive operational complexity. Herein, a strategy for achieving fully decoupled four-channel phase modulation by stacking half-wave plate meta-molecules and chiral meta-molecules is proposed. This strategy directly establishes an explicit functional relationship between the structural phase shifts, rotation angles, and the phases of the four CP channels. Based on this strategy, we designed two chiral free-standing bilayer metasurfaces that can, respectively, achieve vortex light generation and holographic imaging within the four CP channels. The mode purity values of the generated vortex beams exceed 85%, and the crosstalk between the four-channel holographic images is negligible. To demonstrate the application potential of this multi-channel phase modulation strategy, the holographic encryption of target images within twelve angular momentum channels was also performed. The proposed strategy for complete phase decoupling holds broad application prospects in high-capacity optical information encryption and multi-channel vortex beam generation.