Active metamaterials: A novel approach to manipulate terahertz waves

Compared to the neighboring infrared and microwave regimes, the terahertz (1 THz = 1012 Hz) regime is still in need of fundamental technological advances. This derives, in part, from a paucity of naturally occurring materials with useful electronic or photonic properties at terahertz frequencies. This results in formidable challenges in the generation, detection, and creation of devices to efficiently control and manipulate THz waves. Considering the promising potential applications of THz radiation, we need to overcome such material obstacles by actively searching for new materials, or by constructing artificial materials with a desired electromagnetic response. Metamaterials are a new type of artificial composite with electromagnetic properties that derive from their sub-wavelength structure. The potential of metamaterials for THz applications originates from their resonant electromagnetic response, which significantly enhances their interaction with THz radiation. Thus, metamaterials offer a route towards helping to fill the so-called "THz gap". In this work we design a series of novel planar THz metamaterials. Importantly, the critical dependence of the resonant response on the supporting substrate enables the creation of active THz metamaterials. We show that the resonant response can be efficiently controlled using optical or electrical approaches. This has resulted in the invention of efficient THz switches and modulators which will be of importance for advancing numerous real world THz applications.