Terahertz Modulator Based on Vertically Coupled Fano Metamaterial

We introduce a vertical coupling concept to Fano resonance based terahertz (THz) metamaterials, in order to enhance their modulation characteristics. The approach is demonstrated for an asymmetric split-ring structure fabricated from gold with standard micromachining processes on a fused silica substrate. The realized samples are characterized with THz time-domain spectroscopy and the results are in close agreement with the simulation model. Due to the enhanced field concentration facilitated by vertical coupling, we achieve a 95% modulation depth and 35% resonance frequency tunability at 1.23 THz with less than 1-dB inherent loss. The exemplary device shows vertical coupling as an attractive concept for designing efficient modulators for terahertz imaging applications.