Terahertz optical metasurface has a high Q-factor

A metasurface (a surface patterned with periodic subwavelength-sized metallic features on dielectric) can serve as a filter in the terahertz-radiation region, or, with modifications, even a modulator or sensor. Such metasurfaces often are made up of arrays of split-ring or similar resonators. But existing prototypes typically have low resonance quality factors (Q-factors). Researchers at Philipps-Universität Marburg (Marburg, Germany) and INRS-EMT (Varennes, QC, Canada) have proposed and constructed metasurfaces containing arrays of asymmetric D-split resonators (ASDRs); the resulting in-phase oscillations of antisymmetric electrical currents lead to lower radiation losses and a higher Q than for conventional asymmetric split resonators (ASRs).

With a size of 300 μm, each unit cell in the prototype contains two oppositely facing D-shaped metal resonators, each with a cut in it more than halfway down the curved side. Fabricated on a fused-silica substrate, the metal shapes are made of a thin chrome buffer layer and 200 nm of gold; the array size is 32 × 32. Measurements performed by a terahertz time-domain spectrometer show three resonances at 300, 509, and 717 GHz, with a Q factor as high as 30 for the ASDR, as opposed to less than 20 for an ASR. Contact Christian Jansen at [email protected].