Tunable structures and modulators for THz light

We review recent results of both experimental and theoretical work aimed at developing tunable devices with optical properties in the THz range controllable by an external parameter. The presented devices include a semiconductor platelet, strontium titanate based elements and one-dimensional photonic crystals with defects. We show that it is possible to strongly modulate the complex permittivity in the THz range by light illumination, temperature and voltage, and the experimental results obtained by time-domain terahertz spectroscopy are found to be in a very good agreement with theoretical calculations. The control by illumination or applied bias enable a very fast modulation of the THz waves which is useful for prospect applications e.g. in the domain of communications.