Circular dichroism and sensing properties of a chiral metasurface absorber

Chiral metasurfaces can generate differential responses to left-handed and right-handed circularly polarized light, i.e., circular dichroism (CD), offering a novel platform for highly sensitive biochemical sensing. This paper proposes and numerically investigates a chiral metasurface absorber operating in the mid-infrared band. The absorber features a metal-insulator-metal (MIM) three-layer configuration, with its top layer comprising a chiral metasurface of asymmetric split-ring resonators (SRRs). Through systematic finite-element-method simulations, its absorption characteristics, circular dichroism, and underlying tuning mechanisms are analyzed. The results indicate that under right-handed circularly polarized (RCP) light illumination, the structure achieves strong absorption exceeding 90% at a wavelength of 5.235 μm, accompanied by a high absorption-based CD value of 0.647. The resonance wavelength and CD strength can be effectively tuned by adjusting the rotation angle of the split-ring. Furthermore, the structure demonstrates promising refractive index sensing capabilities, with a sensitivity reaching up to 367.4 nm/RIU. This study provides an effective design strategy for developing high-performance, tunable chiral optical sensors and devices.