Simultaneous control of amplitude and phase via shifting isotropy to anisotropy for achieving holographic meta-mirror

Although the emerging isotropic and uniaxially anisotropic metasurfaces have been demonstrated to provide diverse ways for achieving the manipulation of electromagnetic waves, the simultaneous control of both amplitude and phase with designated spin states is still an academic challenge, especially in microwave domain. Here, a paradigm of shifting meta-atom symmetry is proposed to push the development of this difficult issue. A split-ring structure with four identical gaps is applied as a proof-of-principle. By properly arranging the relative positions of four gaps, the electromagnetic characteristics of the meta-atom can be shifted from isotropy to anisotropy. The amplitude of the cross-polarized component of reflective electromagnetic wave is smoothly changed from 0 to 1. Assisted by the Pancharatnam-Berry phase principle, the phase manipulation of anisotropic meta-atom is governed by the control of pivoting. The phase gradient metasurface with uniform amplitude modulation is used as preliminary verification. Subsequently, the complex-amplitude holographic meta-mirrors are designed to promote the proposed paradigm to the application level. Numerical simulations and experimental demonstrations are carried out to reconstruct the holographic images of “B”, “I”, and “T”. Encouragingly, the proposed paradigm may be extended in the applications of circular polarized meta-devices and on-chip systems.