Temperature‐Controlled Optical Activity and Negative Refractive Index

Meng Liu,Biaobing Jin,Eric Plum,Hua Li,Shaoxian Li,Caihong Zhang,Xueqian Zhang,Weili Zhang,Quan Xu,Chongwen Zou,Jiaguang Han

doi:10.1002/adfm.202010249

Abstract

AbstractChiral media exhibit optical activity, which manifests itself as differential retardation and attenuation of circularly polarized electromagnetic waves of opposite handedness. This effect can be described by different refractive indices for left‐ and right‐handed waves and yields a negative index in extreme cases. Here, active control of chirality, optical activity, and refractive index is demonstrated. These phenomena are observed in a terahertz metamaterial based on 3D‐chiral metallic resonators and achiral vanadium dioxide inclusions. The chiral structure exhibits pronounced optical activity and a negative refractive index at room temperature when vanadium dioxide is in its insulating phase. Upon heating, the insulator‐to‐metal phase transition of vanadium dioxide effectively renders the structure achiral, resulting in absence of optical activity and a positive refractive index. The origin of the structure's chiral response is traced to magnetic coupling between front and back of the structure, whereas the temperature‐controlled chiral‐to‐achiral transition is found to correspond to a transition from magnetic to electric dipole excitations. The use of a fourfold rotationally symmetric design avoids linear birefringence and dichroism, allowing such a structure to operate as tunable polarization rotator, adjustable linear polarization converter, and switchable circular polarizer.

Highlights

Chiral media exhibit optical activity, which manifests itself as differential retarrefractive indices for left- and right-handed circularly polarized electromagnetic dation and attenuation of circularly polarized electromagnetic waves of oppowaves, resulting in polarization rotation site handedness
This is especially true at THz frequencies owing to the large traced to magnetic coupling between front and back of the structure, whereas mismatch of THz wavelengths
The transmission characteristics of the metamaterial, as it transitions from its room temperature chiral state to its high temperature achiral state, were simulated and measured

Summary

Introduction

Chiral media exhibit optical activity, which manifests itself as differential retarrefractive indices for left- and right-handed circularly polarized electromagnetic dation and attenuation of circularly polarized electromagnetic waves of oppowaves, resulting in polarization rotation site handedness This effect can be described by different refractive indices for left- and right-handed waves and yields a negative index in extreme cases. The insulator-to-metal phase transition of vanadium dioxide effectively renders the structure achiral, resulting in absence of optical activity and a positive refractive index. The origin of the structure’s chiral response is natural materials, requiring interaction lengths that are large in comparison to the wavelength to accumulate significant polarization changes This is especially true at THz frequencies owing to the large traced to magnetic coupling between front and back of the structure, whereas mismatch of THz wavelengths Optical activity corresponds to different refractive index for one circular polarization or the other.[15,16]

Methods

Results

Conclusion