Spin‐Selective Absorption and Geometric‐Phase Modulation via Chiral Metasurface in Triple Bands

Abstract Metasurfaces with spin‐selective reflection or transmission functions for circularly‐polarized (CP) incident waves have aroused researchers' great attention. However, current spin‐selective metasurface designs have yet to mature into a practical method due to the limitations of single operating band or inefficient phase modulation. Herein, a novel chiral meta‐atom is proposed, exhibiting spin‐selective absorption/reflection functions for dual‐orthogonal CP incident waves at three different operating bands. More significantly, the Pancharatnam–Berry phase theory is introduced at all working frequencies to generate a full 2π reflection phase modulation by rotating the chiral resonator, and the three distinct absorption bands remain almost constant with the rotation. Theoretical results indicate that high absorption can separately act on left‐handed or right‐handed CP incident waves at triple bands, and meanwhile, the other incident wave with different handedness is efficiently reflected without changing the handedness. As a proof of concept, two tri‐band meta‐devices with spin‐selective anomalous reflection and spin‐selective orbital angular momentum generating functions are designed and experimentally characterized, both of which exhibit excellent spin‐dependent bi‐functional performances at three different operating bands. The research results provide a promising route to realize spin‐selective meta‐devices with multi‐band operating modes in wireless communication systems and multispectral imaging and information encryption fields.