Gradient Chiral Metamirrors for Spin‐Selective Anomalous Reflection

Abstract

Metasurfaces, the phase‐engineered quasi‐2D interfaces, have attracted intensive interest due to their great capabilities in manipulating the reflection, refraction and transmission of electromagnetic waves. Here, we demonstrate the design and realization of a gradient chiral metamirror tailored for spin‐selective anomalous reflection based on the theory of Pancharatnam‐Berry phase. Asymmetric split ring resonators are employed as the basic meta‐atoms for strong circular dichroism. Dispersionless phase discontinuities are achieved by adjusting the orientation of the meta‐atoms, and spin‐dependent absorption is realized by introducing a chiral resonance. Theoretical results predict both broadband beam deflection and spin‐selective absorption for circularly polarized waves in a designer metamirror. Experimental verification of this bifunctional performance is implemented at microwave frequencies and the measured results agree well with the simulation ones. Such chiral metamirrors could pave an avenue towards spin‐selective modulation of the wavefront and might find promising applications in planar electromagnetic devices.

Spin Momentum–Locked Surface States in Metamaterials without Topological Transition

“…Under this assumption, the chirality of the material is zero so that the fundamental modes are separated through their polarizations (similar to TE and TM decoupling), which makes the topological invariants vanish for regular non‐dispersive materials . Moreover, this assumption reduces the difficulty of material design and fabrication since the magneto‐electric (ME) effect of a planar structure can only make the perpendicular and be coupled such as in unbalanced split‐ring resonators(USRRs) …”

Design and Experimental Demonstration of Impedance-Matched Circular-Polarization-Selective Surfaces with Spin-Selective Phase Modulations

“…For example, at the cost of increased complexity in fabrication, a curved CPSS has been demonstrated in [26] where the CPSS is physically shaped to obtain the necessary reflection phase shifts from the wave propagation. On the other hand, planar phase-gradient chiral metasurfaces have also been demonstrated that take advantage of the geometrical phase shift [27][28][29][30]. In particular, these phase-gradient chiral metasurfaces realize spin-selective phase modulations by rotating individual chiral unit cells to acquire the Pancharatnam-Berry phase shifts along their surfaces [31].…”

Asymmetric dual‐band linear‐to‐circular converter by bi‐layered chiral metamaterial

“…Metamaterials, which are artificial sub‐wavelength periodic structures, have opened up a new avenue toward efficient manipulation of light due to their unique optical properties. Those are valuable in optical rotation, asymmetric transmission (AT), and polarization conversion . Circular‐to‐circular, linear‐to‐linear, linear‐to‐circular (LTC) polarization converters can be realized by different structural designs.…”

“…Those are valuable in optical rotation, 8,9 asymmetric transmission (AT), 10,11 and polarization conversion. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] Circular-tocircular, 12,13 linear-to-linear, [14][15][16] linear-to-circular [17][18][19][20][21][22][23][24][25][26] (LTC) polarization converters can be realized by different structural designs. Meanwhile, in order to obtain wider bandwidth, higher transmission efficiency (TE), conversion efficiency (CE) and polarization extinction ratio (PER), converters in transmission mode are usually implemented using chiral metamaterials (CMMs) with strong conversion dichroism 18,19 (CD) accompanied by AT.…”