Switchable Chiral Mirrors

Mirrors are widely used for redirection of electromagnetic waves in optical systems, making them arguably the most irreplaceable optical component. Metamaterial-based chiral mirrors, composed of a 2D-chiral planar metallic structure backed by a conventional mirror, reflect one circular polarization without changing its handedness, while absorbing the other. Here, three types of switchable chiral mirror are demonstrated. Switching from a chiral mirror to either a conventional mirror, a handedness-preserving mirror, or a chiral mirror of opposite handedness, is realized. These advances are underpinned by switching the handedness of 2D-chiral metamaterial and the associated effect of circular conversion dichroism, which is reported here for the first time. Switching is achieved by exploiting the temperature-activated dielectric-to-metal phase transition of vanadium dioxide to modify the symmetry and chirality of the metamaterial's resonators. Current distributions explain the temperature-controlled optical properties by handedness-selective excitation of reflective electric dipole and absorbing magnetic dipole modes.