Terahertz (THz) radiation, sandwiched between traditional microwave and visible light, is the electromagnetic spectrum with the frequency defined from 0.1 to 10 THz (1THz=1012Hz). Until recently, due to the difficulty of generating and detecting techniques in this region, THz frequency band remains unexplored compared to other range and tremendous effort has been made in order to fill in “THz gap” . (Zhang & Xu, 2009)