Decoupled Phase Modulation for Circularly Polarized Light via Chiral Metasurfaces

Metasurfaces have emerged as one highly vibrant frontier in the field of nanophotonics, since they enable some unique and practical means to modulate the phase, polarization, angular momentum, and spatial field distribution through structural engineering. However, the current methods of phase modulation based on the propagation phase and Pancharatnam-Berry phase are typically interrelated between two eigen spin states for each singlestep modulation. It means that when the phase of left-handed circularly polarized (LCP) light is modulated by a metasurface, the phase of right-handed circularly polarized (RCP) light will change as well, imposing substantial constraints if spin-decoupled or spin-independent applications are sought. In this paper, we numerically and experimentally demonstrate a new phase modulation pathway based on chiral metasurfaces consisting of V-shaped plasmonic apertures, which enable fully decoupled phase modulation for the two eigen spin states. Two enantiomers are proposed to achieve the desired phase decoupling. Specifically, the enantiomer can manipulate the phase of the LCP component of a light beam without changing the phase of the RCP component, and vice versa. Our method expands the methods of phase engineering and can help us design novel devices for a wide range of applications, including polarimetric imaging, chiroptical detection, molecular spectroscopy, and quantum information processing.