Dual-channel sensing by combining geometric and dynamic phases with an ultrathin metasurface

Ultrathin metasurfaces consisting of subwavelength anisotropic plasmonic resonators with spatially variant orientations are capable of generating local geometric phase profiles for circular polarizations (CP) and can be used for multiplexing of electromagnetic waves. As the geometric phase solely depends on the orientation of dipole antennas, the phase profiles cannot be changed dynamically with external environment once the structure is fabricated. Here, by incorporating geometric phase and resonance-induced dynamic phase in a monolayer of nano gold antennas, we show that phase profiles of different spin components can vary independently through modification of the external environment. Specifically, the intensities of the + 1 and -1 order diffracted waves vary asymmetrically with the refractive index of surrounding media, forming a dual-channel sensing system. Our dual-channel sensing method exhibits very high signal-to-noise ratio and stability for sensing of liquid, monomolecular layer and even nanoscale motion, which will have potential applications in various fields, including biosensing, precision manufacturing, monitoring of environment, and logic operations.