Abstract:

Planar metamaterials have been designed, fabricated, modeled and characterized at terahertz (THz) frequencies, which is one of the most technically challenging and least developed regime in the electromagnetic spectrum. Their resonant properties derive from the structural geometry and dimensions of the split-ring resonators serving as the metamaterial basic building blocks. By incorporating natural materials, e.g. semiconductors, as the metamaterial substrates or in the critical regions of the metamaterial elements, the metamaterial resonant properties can be dynamically or actively controlled through external stimuli, such as photoexcitation and voltage bias. We demonstrated all optical switching of THz radiation through photoexcitation of the metamaterial semiconducting substrate, e.g. intrinsic GaAs wafers or GaAs:ErAs nanoisland superlattices. In the latter case the carrier lifetime can be engineered from sub-picosecond to tens of picoseconds, which determines the ultrafast switching time of the THz radiation. More interestingly, when fabricating the planar metamaterials on a semiconducting substrate with a thin doping layer, the metamaterial resonant response can be actively switched through the application of a voltage bias, due to the voltage-controlled depletion near the split gaps. The solid-state metamaterial devices operate at room temperature and are capable of state-of-the-art performance in electrical modulation of THz intensity and phase, which are correlated and further enable a broadband modulation of impulsive THz radiation in the time domain measurements. I will also discuss other recent progress from our team in THz metamaterials and devices, including frequency agile metamaterials, metamaterial antireflection coating, and superconductor metamaterials.
 
 
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