Extrinsic optical activity in all-dielectric terahertz metamaterial

Chiral metamaterials have attracted wide interest because strong optical activity at designed frequencies could be achieved beyond that in natural materials. Here we propose an all-dielectric metamaterial with strong extrinsic circular dichroism and circular birefringence by periodically arranging symmetry-broken dielectric Mie resonators at terahertz frequencies. The strong interaction between the electric and magnetic resonances from circularly polarized incident waves dominates the performance of the all-dielectric metamaterial, which exhibits a 60% circular dichroism in transmission and a polarization rotation angle of 60^◦ at maximum, respectively. Additionally, the spectral range of the circular dichroism with preserved amplitude can be adjusted continuously in the frequency range from 0.67–0.79 THz by tuning the tilt angle of the incident wave. Our findings will be of great potential in polarization control applications such as asymmetric transmission, optical isolation, and on-chip chiral manipulation.