Interference‐Assisted Independent Amplitude and Phase Manipulation with Broadband Chiral Meta‐Mirror

Abstract

Achieving simultaneous amplitude and phase control is crucial in various spin‐selective optical applications, particularly for chiral mirrors that exhibit distinct responses when illuminated by orthogonal circularly polarized waves. However, conventional chiral metasurface approaches for amplitude manipulation can only be implemented by adjusting absorption, which limits the bandwidth due to the dispersion nature of the meta‐structure and cannot ensure that the chiral mirror output only one circular polarization component with independent amplitude and phase manipulation at multi‐polarization incidence. Here, an interference‐mechanism‐assisted methodology is proposed for broadband chiral meta‐mirrors with independent control over amplitude and phase. Such controls are achieved by simply setting the rotation angle of each meta‐atom in the integrated quad‐atom structure. The rotation angle of each meta‐atom and the difference between adjacent meta‐atoms rotation angles provide flexible degrees of freedom for controlling phase and amplitude, respectively. Notably, this mechanism stemming from the Pancharatnam‐Berry phase allows for wideband operation due to its dispersion‐free nature of phase control. As proof‐of‐principle demonstrations, numerically verify a series of amplitude‐tailorable phase‐gradient meta‐mirrors and experimentally demonstrate a broadband chiral Airy beam generator. This method offers a straightforward solution for spin‐selective amplitude/phase manipulation which may have the potential to advance the engineering application of chiral metasurfaces.