Research On Terahertz Modulation Based On Surface Plasmon

With the rapid development of terahertz science and technology,a series of the research of the terahertz functional devices has been widely concerned.It provides an new thought of designing terahertz modulators by using the extraordinary optical transmission of terahertz metamaterial and graphene with high electronic mobility,high carrier concentration and tunable characteristic,which possesses huge application potential.When satisfying the wave vector matching condition in terahertz spectrum,periodic subwavelength structures can excite the surface plasmon on the surface of metal resulting in the extraordinary optical transmission effect and high transmission resonance peaks in the spectrum.Furthermore,the transmission peaks caused by propagating surface plasmon possess excellent tunable characteristic.It can extract the dispersion formula of propagating surface plasmon by means of Maxwell equations.According the dispersion formula,When changing the effective permittivity of the external dielectric above the metal,it can change the resonance frequency of transmission peak and realize the terahertz amplitude modulation.This article mainly studies to adjust the resonance peak by means of light control and electronic control methods to realize the terahertz amplitude modulation.First,we theoretically and numerically investigated the influence of the external dielectric on the metallic periodic structure.The metamaterial structure using silicon as the dielectric overlayer was produced and measured in the terahertz system.The experiment results confirm the terahertz modulation by surface plasmon and the photoconductive effect of silicon.Second,the basic material parameter of gallium arsenide was measured and the results indicate the photoconductive characteristic is superior to silicon.The metamaterial structure using gallium arsenide as the dielectric overlayer was also produced and measured.The experiment results reveal the modulation depth can be improved through using gallium arsenide as the overlayer.In addition,a graphene metamaterial terahertz modulator through integrating the metallic periodic subwavelength structure and a self-gated pair of graphene layers was proposed utilizing the unique properties of graphene.We theoretically and numerically investigate its characteristic of extraordinary optical transmission.The modulator can realize low insertion losses,low return losses,low gate voltage and high modulation depth by simulation optimization.