Fast Terahertz Wave Switch/Modulator Based on Photonic Crystal Structures

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Abstract
In this paper, an optically controlled fast switch or modulator in THz wave is proposed and analyzed. The proposed structure is based on two dimensional photonic crystals constructed by triangular lattice of SiO2 rods in air or air holes in MgO material with a GaAs layer in the middle as a defect. Excitation of the structure by the probe pulse of 810 nm wavelength causes the generation of free carriers at the surface of the defect layer and leads to increasing the loss of the layer. Therefore, the switching or modulation of the defect mode in the band gap of the structure occurs, which is very fast in order of hundred picoseconds. Terahertz wave with frequency of the defect mode copropagated with the probe signal can be switched or modulated. The band gap and defect mode can be engineered by the geometry of the structure.