Switchable fractional perfect composite vortex encryption based on double-layer metasurface

Abstract

We propose a double-layer metasurface to realize the polarization switching of fractional perfect composite vortex beams (FPCVBs). The metasurface is designed by the Jones matrix formalism and optimized through the “Random Forest” machine learning algorithm, achieving high polarization switching efficiency. The grafted-FPCVBs are presented with featuring multivariate topological charges, and double-ring FPCVBs are achieved with independent on/off modulation and shaping transformation of inner and outer ring intensities. These capabilities unlock orbital angular momentum density modulation and light field reconfiguration in composited light architectures. Moreover, we design an optical encryption protocol inspired by the hierarchical structure of chinese characters, where semantic radicals are mapped to polarization-encoded FPCVBs. These innovations present significant potential for applications in optical information security, particle manipulation, and next-generation photonic communications.