Photonic spin-selective perfect absorptance on planar metasurfaces driven by chiral quasi-bound states in the continuum,Nanoscale

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Photonic spin-selective perfect absorptance on planar metasurfaces driven by chiral quasi-bound states in the continuum
Nanoscale ( IF 5.8 ) Pub Date : 2023-03-02 , DOI: 10.1039/d3nr00055a
Hongju Li ₁ , Hongmiao Zhou ₁ , Gangao Wei ₁ , Hangsheng Xu ₁ , Meng Qin ₁ , Jianqiang Liu ₂ , Feng Wu ₃

Affiliation

Optical metasurfaces with high-quality-factor resonances and selective chirality simultaneously are desired for nanophotonics. Here, an all-dielectric planar chiral metasurface is theoretically proposed and numerically proved to support the astonishing symmetry-protected bound state in the continuum (BIC), due to the preserved π rotational symmetry around the z axis and up-down mirror symmetry simultaneously. Importantly, such BIC is a vortex polarization singularity enclosed by elliptical eigenstate polarizations with non-vanishing helicity, owing to the broken in-plane mirror symmetry. Under the oblique incidence, companied by the BIC transforming into a quasi-BIC (Q-BIC), the strong extrinsic chirality manifests. Assisted by the single-port critical coupling, the planar metasurface can selectively and near-perfectly absorb one circularly polarized light but non-resonantly reflect its counterparts. The circular dichroism (CD) approaching 0.812 is achieved. Intriguingly, the sign of CD (namely, the handedness of the chiral metasurface) can be flexibly manipulated only via varying the azimuthal angle of incident light, due to the periodic helicity sign flip in eigen polarizations around the BIC. Numerical results are consistent with the coupled-mode theory and multipole decomposition method. The spin-selective metasurface absorber empowered by the physics of chiral Q-BICs undoubtedly may promise various applications such as optical filters, polarization detectors, and chiral imaging.

中文翻译：

由连续体中的手性准束缚态驱动的平面超表面上的光子自旋选择性完美吸收率

纳米光子学需要同时具有高质量因子共振和选择性手性的光学超表面。在这里，由于在z周围保留了 π 旋转对称性，因此理论上提出了一种全电介质平面手性超表面，并通过数值证明支持连续体 (BIC) 中惊人的对称保护束缚态轴和上下镜像同时对称。重要的是，由于面内镜对称性的破坏，这种 BIC 是由具有非零螺旋性的椭圆本征态偏振包围的涡旋偏振奇点。在倾斜入射下，伴随着BIC转变为准BIC（Q-BIC），强烈的外在手性表现出来。在单端口临界耦合的协助下，平面超表面可以选择性地且近乎完美地吸收一种圆偏振光，但非共振地反射其对应物。实现了接近 0.812 的圆二色性 (CD)。有趣的是，CD 的符号（即手性超表面的手性）只能通过由于 BIC 周围特征偏振的周期性螺旋符号翻转，改变入射光的方位角。数值结果与耦合模理论和多极分解方法一致。由手性 Q-BIC 物理学支持的自旋选择性超表面吸收器无疑有望应用于各种应用，例如光学滤波器、偏振检测器和手性成像。

更新日期：2023-03-06

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