Dissymmetrical planar gratings enabled actively chiral perfect absorber

Chiral perfect absorbers (CPAs) can completely absorb one kind of circularly-polarized light while reflecting the other, and have potential applications in fields such as chiral Fabry–Pérot cavity, chiral light emission, and chiral biosensors. In this work, we present a high-performance chiral perfect absorber comprising a dissymmetrical planar chiral grating (DPCG), a dielectric gap layer, and a metallic film. Circular polarization conversion induced by the anisotropic chirality of the DPCG introduces destructive interference among multiple reflected beams within the cavity, resulting in selective perfect absorption of circularly polarized light. This selectivity is closely related to the geometric chirality of the DPCG. By replacing the gap layer with a phase-change material such as VO2, the effective optical path length can be dynamically tuned via external stimuli, thereby modulating the interference among multiple reflected beams and enabling actively tunable chiral perfect absorption. Systematic studies show that the optimized CPA exhibits strong selective absorption, with a reflective circular dichroism of up to ~0.94. When VO2 is employed as the gap material, the modulation sensitivities of the device reach 2728 RIU-1 at d=100 um and 0.064 nm−1 at n=4.0, respectively, and the corresponding temperature sensing sensitivity reaches 2.7×10-8 ℃. These performances surpass those of previously reported studies. Combined with the simple geometry and fabrication feasibility of the dissymmetrical planar chiral grating, the proposed CPA demonstrates strong potential for practical applications.