Transition from anisotropic to isotropic optical absorption in core-shell square nanowires tuned by anti-crossing engineering.

ABSTRACT

The transition from anisotropic to isotropic optical properties in nanostructures plays an important role in developing next-generation intelligent photonic devices. Currently, core-shell nanostructures, frequently accompanied by different growth rates, are typically characterized by anisotropic optical properties at mid-infrared wavelengths. This inherent anisotropy, however, poses formidable challenges in achieving optical isotropy. In this work, an electric field is employed to transform the optical anisotropy of the off-centered core-shell square nanowires into optical isotropy. Based on the finite difference method, the results show that by tuning the electric field reasonably, the anti-crossing behavior of energy levels can be induced to align the energy structures in both eccentric and concentric nanowires. Although the optical anisotropy is strongly dependent on the distance and direction of the core shift, we marks, to the best of our knowledge, the first demonstration that the restored electronic states can effectively neutralize the polarization sensitivity, achieving isotropic optical absorption with wavelengths longer than 10 µm. Our finding indicates that the anti-crossing behavior of energy levels can serve as a viable mechanism to achieve switchable optical isotropy.