Ma Zhijie, Li Yi, Li Yang, Gong Yandong, Maier Stefan A, Hong Minghui
Opt Express. 2018 Mar 5;26(5):6067-6078. doi: 10.1364/OE.26.006067.
Planar optical chirality of a metasurface measures its differential response between left and right circularly polarized (CP) lights and governs the asymmetric transmission of CP lights. In 2D ultra-thin plasmonic structures the circular dichroism is limited to 25% in theory and it requires high absorption loss. Here we propose and numerically demonstrate a planar chiral all-dielectric metasurface that exhibits giant circular dichroism and transmission asymmetry over 0.8 for circularly polarized lights with negligible loss, without bringing in bianisotropy or violating reciprocity. The metasurface consists of arrays of high refractive index germanium Z-shape resonators that break the in-plane mirror symmetry and induce cross-polarization conversion. Furthermore, at the transmission peak of one handedness, the transmitted light is efficiently converted into the opposite circular polarization state, with a designated geometric phase depending on the orientation angle of the optical element. In this way, the optical component sets before and after the metasurface to filter the light of certain circular polarization states are not needed and the metasurface can function under any linear polarization, in contrast to the conventional setup for geometry phase based metasurfaces. Anomalous transmission and two-dimensional holography based on the geometric phase chiral metasurface are numerically demonstrate as proofs of concept.
超表面的平面光学手性测量其对左旋和右旋圆偏振（CP）光的差分响应，并控制CP光的不对称传输。在二维超薄等离子体结构中，圆二色性理论上限制在25%，并且需要高吸收损耗。在此，我们提出并通过数值证明了一种平面手性全介质超表面，对于圆偏振光，它表现出巨大的圆二色性和超过0.8的传输不对称性，损耗可忽略不计，且不会引入双各向异性或违反互易性。该超表面由高折射率锗Z形谐振器阵列组成，这些谐振器打破了面内镜像对称性并诱导交叉偏振转换。此外，在一种手性的传输峰值处，透射光被有效地转换为相反的圆偏振态，其特定的几何相位取决于光学元件的取向角。通过这种方式，与基于几何相位的超表面的传统设置相比，不需要在超表面之前和之后设置光学元件来过滤特定圆偏振态的光，并且该超表面可以在任何线性偏振下工作。基于几何相位手性超表面的异常传输和二维全息术通过数值证明作为概念验证。
