Ultranarrowband Chiral Absorbers in the Visible Region Based on Brillouin Zone Folding Metasurfaces

Chiral perfect absorbers that enable the handedness-dependent near-unity absorption of circularly polarized light are highly desirable for enhancing various chiral interactions. However, the experimental realization of ultranarrowband absorbers with extreme chiral responses remains challenging. Here, we realize such chiral absorbers by incorporating Brillouin zone folding and mirror symmetry breaking in the design of planar dielectric metasurface. When the metasurface is backed by a reflection mirror, strong chiral absorption with ultranarrow line width can be achieved in the normal direction. We experimentally achieve a substantial differential absorptance of 0.75 with an ultranarrow line width of 1.4 nm in the visible region. Furthermore, by leveraging handedness-dependent strong field enhancement, high levels of chiral emission with a luminescence line width of 1.75 nm are demonstrated from quantum dots coated on the absorber surface. Our findings may unlock interesting opportunities in chiral photodetectors, optical filters, nonlinear optics, light sources, and quantum photonic devices.