Abstract
Chiral materials can exhibit different levels of transmission for opposite propagation directions of the same electromagnetic wave. Here we demonstrate thermal switching of asymmetric transmission of linearly polarized terahertz waves. The effect is observed in a terahertz metamaterial containing 3D-chiral metallic inclusions and achiral vanadium dioxide inclusions. The chiral structure exhibits pronounced asymmetric transmission at room temperature when vanadium dioxide is in its insulator phase. As the metamaterial is heated, the insulator-to-metal phase transition of vanadium dioxide effectively renders the structure achiral and the transmission asymmetry vanishes. We demonstrate the effect numerically and experimentally, describe it analytically and explain the underlying physical mechanism based on simulated surface current distributions. Potential applications include directionally asymmetric active devices as well as intensity and polarization modulators for electromagnetic waves.
Highlights
Polarizations that interchange for opposite propagation directions[17,18,19,20,21,22]
Using the insulator-to-metal phase transition of vanadium dioxide (VO2)[34,35], we effectively switch between different metamaterial symmetries, resulting in thermal switching of directionally asymmetric transmission of linearly polarized terahertz waves
The metamaterial was fabricated by conventional photolithography and its transmission and polarization properties were characterized by THz time-domain spectroscopy as explained in the Methods
Summary
Polarizations that interchange for opposite propagation directions (linear conversion dichroism)[17,18,19,20,21,22]. Using the insulator-to-metal phase transition of vanadium dioxide (VO2)[34,35], we effectively switch between different metamaterial symmetries, resulting in thermal switching of directionally asymmetric transmission of linearly polarized terahertz waves. In order to design metamaterials with controllable asymmetric transmission for linearly polarized waves at normal incidence, we analyze the material symmetries that lead to presence and absence of the effect. (All formulas apply without sample rotation when describing opposite illumination directions in different coordinate systems defined by wave propagation along +z. For forward illumination, these coordinates coincide with the lab coordinates. The transmission asymmetry for linearly polarized waves is characterized by
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