Broadband Spin-Selective Wavefront Manipulations Based on Pancharatnam–Berry Coding Metasurfaces

Abstract

Spin-selective reflection metadevices are usually realized by using chiral metamirrors that can reflect one state of circularly polarized (CP) waves and restrain the other one. However, most of the chiral metamirrors only exhibit chirality in a narrow band, which may impede their potential applications. Here, we propose a Pancharatnam–Berry (PB) coding metasurface composed of the spin-decoupled elements to realize broadband spin-selective reflections with arbitrary wavefront manipulations. The spin-selective anomalous reflection is designed and measured to validate the performance of the proposed PB coding metasurface. Both simulation and experiment results show that the designated CP wave can be efficiently reflected without reversing the spin state, while at the same time, its orthogonally polarized wave is suppressed by random diffusion, in a broad band from 16 to 24 GHz. The results also reveal that the proposed PB coding metasurface has the chiral-like characteristics, even though it is composed of nonchiral meta-elements.

Non‐Interleaved Polarization‐Frequency Multiplexing Metasurface for Multichannel Holography

“…On the other hand, it is well known that the CP waves can be flexibly controlled by the meta‐atoms that satisfy the propagation phase (φ β ), and the spin decoupling of LCP and RCP waves can be further achieved by introducing the geometric phase (φ α ). Specifically, when the meta‐atoms have the same reflection amplitude for u ‐ and v ‐polarized waves ( A u = A v ), and their phase differences satisfy |φ u – φ v | = π, the co‐polarized reflection phases of LCP and RCP waves can be calculated as [ 19,20 ] $$\[ \begin{array}{*{20}{c}}{\left\{ { \begin{array}{*{20}{c}}{{\varphi _{{\rm{LL}}}} = {\varphi _\beta } - {\varphi _\alpha }}\\{{\varphi _{{\rm{RR}}}} = {\varphi _\beta } + {\varphi _\alpha }}\end{array} } \right. }\end{array} \]$$where φ β = φ u and φ α = 2α.…”

“…On the other hand, it is well known that the CP waves can be flexibly controlled by the meta-atoms that satisfy the propagation phase (ϕ β ), and the spin decoupling of LCP and RCP waves can be further achieved by introducing the geometric phase (ϕ α ). Specifically, when the meta-atoms have the same reflection amplitude for u-and v-polarized waves (A u = A v ), and their phase differences satisfy |ϕ u -ϕ v | = π, the co-polarized reflection phases of LCP and RCP waves can be calculated as [19,20]…”

“…Recently, polarization multiplexed metasurfaces were proposed and demonstrated with dual-or multi-channels vectorial holographic displays for linearly polarized (LP) or circularly polarized (CP) waves and negligible polarization cross-talk, which provides new avenues for optical encryption and anti-counterfeiting. [15][16][17][18][19][20][21][22][23][24][25][26][27] Besides, frequency multiplexed metasurfaces, whose constituent elements usually possess multiple resonant modes that are each generated individually at different frequencies, can also achieve multiple independent holographic channels. [28][29][30][31][32][33][34][35] More recently, spatial multiplexing [36][37][38] and momentum multiplexing [39] have also been exploited to enhance the channel capacity of metasurfaces.…”

Bifunctional Integration Performed by a Broadband High‐Efficiency Spin‐Decoupled Metasurface

“…[27][28][29] The quasi-I-shaped meta-atom has been used to fabricate broadband spin-decoupled metasurfaces. [32,34] The main contributions and organization in this section are as follows: 1) In Section 2.1, we elucidate the broadband spin-decoupled criteria for meta-atoms design, that is, Equations (4-6). 2) In Section 2.2, we develop a broadband high-efficiency spin-decoupled meta-atom.…”

“…Some research even exhibits broadband spin-decoupled functions for two generated CP beams. [27,[32][33][34][35][36] However, the asymmetric AA-phase meta-atom may introduce unequal reflection amplitudes for two circular polarizations, which may hinder the high-efficiency design. These meta-atoms in the abovementioned spin-decoupled metasurfaces still have room to be broader frequency bandwidths and higher efficiency.…”