Chirality refers to a geometric phenomenon in which objects are not superimposable on their mirror image. Structures made of nanoscale chiral elements can exhibit chiroptical effects, such as dichroism for left- and right-handed circularly polarized light, which makes these structures highly suitable for applications ranging from quantum information processing and quantum optics to circular dichroism spectroscopy and molecular recognition. At the same time, strong chiroptical effects have been challenging to achieve even in synthetic optical media, and chiroptical effects for light with normal incidence have been speculated to be prohibited in thin, lossless quasi-two-dimensional structures. Here, we report an experimental realization of a giant chiroptical effect in a thin monolithic photonic crystal mirror. Unlike conventional mirrors, our mirror selectively reflects only one spin state of light while preserving its handedness, with a near-unity level of circular dichroism. The operational principle of the photonic crystal mirror relies on guided-mode resonance (GMR) with a simultaneous excitation of leaky transverse electric (TE-like) and transverse magnetic (TM-like) Bloch modes in the photonic crystal slab. Such modes are not reliant on the suppression of radiative losses through long-range destructive interference, and even small areas of the photonic crystal exhibit robust circular dichroism. Despite its simplicity, the mirror strongly outperforms earlier reported structures and, contrary to a prevailing notion, demonstrates that near-unity reflectivity contrast for opposite helicities is achievable in a quasi-two-dimensional structure.

手性是指一种几何现象，其中对象不能叠加在其镜像上。由纳米级手性元素制成的结构可以表现出按摩效应，例如左旋和右旋圆偏振光的二色性，这使得这些结构非常适合从量子信息处理和量子光学到圆二色性光谱和分子识别的应用。同时，即使在合成光学介质中，要达到强大的按摩效果也具有挑战性，并且推测在薄的，无损的准二维结构中，对于垂直入射光的按摩效果是被禁止的。在这里，我们报告了在薄的整体式光子晶体镜中巨大的按摩效应的实验实现。不像传统的镜子 我们的反射镜在保持其惯性的同时，选择性地仅反射一种自旋光，并且具有几乎统一的圆形二向色性。光子晶体镜的工作原理依赖于导模共振（GMR），同时激发光子晶体平板中泄漏的横向电（TE-like）和横向磁（TM-like）Bloch模式。这样的模式不依赖于通过远距离破坏性干扰来抑制辐射损耗，甚至光子晶体的小面积也表现出鲁棒的圆二色性。尽管其简单，但该镜子仍大大优于先前报道的结构，并且与流行的概念相反，该镜子表明在准二维结构中可以实现相对螺旋的近统一反射率对比度。