Optical Wavelength-dependent THz Wave Modulation based on Graphene Coated Germanium

Optical Hz wave modulator based on semiconductor is broad used in THz imaging area due to convenient to realize. However, for a long time, the laser wavelength influence to the modulation properties is not clear. Germanium and graphene coated germanium upon different laser wavelength (638, 915 and 1550 nm) laser irradiation were investigated to clear the above influence. As a result, the THz wave modulation depth increase with the laser wavelength due to the surface recombination. And the results were proven by discussing the modulation enhancement of graphene coated germanium. In addition, the short wavelength laser would lead to slow modulation rate. As a result, it is a novel method to improve the THz modulation depth and modulation rate by using long wavelength laser.