Breaking planar symmetries by a single layered metasurface for realizing unique on-chip chiroptical effects

Abstract

Chiroptical effects are instrumental for various intriguing applications like chiro-optical spectroscopy and chiral imaging. Their on-chip realization can open novel avenues for the demonstration of these applications at a miniaturized scale. One can leverage the unprecedented flexibility of metasurfaces to tailor the spinning light meticulously for realizing these chiroptical effects at a compact scale. Here, we present a unique methodology to effectively achieve such chiroptical effects by a single-layered metasurface consisting of a two-dimensional array of C2-symmetric meta-atoms. These meta-atoms are carefully engineered to break the mirror and n-fold (n=2) rotational symmetries. The optimized meta-atoms reflect 84% (cross-polarized light) under right circularly polarized illumination and transmit 80% (cross-polarized light) when left circularly polarized light is impinged. Such optical responses result in a giant asymmetric transmission (AT) of 80% in the reflection and 74% in the transmission mode along with full phase control (of 0-2π). To verify this asymmetric behavior in transmission and reflection, we implemented holograms both in the forward and backward directions. The proposed design methodology enables the realization of chiroptical effects via compact on-chip which can find promising applications in chiral sensing and imaging.