Strong circular dichroism with high quality factor enabled by hyperbolic material α-MoO3 in mid-infrared range

As an emerging natural biaxial hyperbolic material, α-phase molybdenum trioxide (α-MoO3) exhibits the excellent anisotropy and unique electromagnetic manipulation properties, which further stimulates the potential for polarization manipulation. Here, a Fabry-Perot cavity chiral structure based on multilayer films of α-MoO3 and BaF2 is presented, which exhibits excellent circular dichroism (CD) by displaying different reflectance properties for left-hand circular polarization and right-hand circular polarization light in the mid-infrared range. The numerical simulation results demonstrate that the chiral structure exhibits a remarkable absorption efficiency of 0.99 for left circularly polarized light at a wavelength of 12 μm, accompanied by a maximum CD in reflection of 0.93 and a resonant quality factor (Q-factor) of 111. This exceptional performance arises from the relative twist between α-MoO3 and the underlying BaF2 thin film, which simultaneously breaks the rotational and mirror symmetries of the chiral structure. To gain a deeper understanding, we further investigate the influence of film thickness and relative rotation angle on the optical properties of the chiral structure. By adjusting the geometric parameters of the chiral structure, it becomes possible to tune the chiral resonance wavelength and the corresponding CD value, providing a novel approach for the development of tunable chiral optical devices. This study offers new insights into the fabrication of low-cost chiral structures with high-Q resonances and their potential applications in the mid-infrared range, laying the foundation for the development of more powerful and controllable chiral optical devices.