Enhancement of EO sampling sensitivity for THz waves by using super-focusing effect in metallic parallel plate waveguide
Abstract
We have succeeded in enhancing the sensitivity of electro-optic (EO) sampling for terahertz (THz) waves by using a metallic parallel plate waveguide structure. The EO sampling signal is proportional to the incident THz electric field on the EO crystal. However, focusing of THz electric field by ordinary optics, such as lenses, is limited by the diffraction effect. In this research, we use a tapered metallic parallel plate waveguide (V-groove waveguide) to collect and focus THz waves into the sub-wavelength gap of a parallel plate. Furthermore, by using a thin EO crystal (LiNbO3 crystal) attached to the end of the metallic waveguide structure, we have suppressed diffraction effects. As the result we achieved about 20 times enhancement of total EO sampling signal compared to the case without the metallic waveguide structure.