Research On Phase Modulation Of Polarization State And Detector Of Terahertz Lightwave

Terahertz is usually defined as a wavelength of 30-3000 μm range,the frequency occupy 0.1-10 THz,its band is between microwave and infrared,and is located in the electronics and photonics fields.Therefore,compared with other electromagnetic waves,terahertz has the characteristics of both electrons and photons.It has many unparalleled properties,such as low energy,safety,high penetration,fingerprint spectrum and broadband.It can be widely recognized in nondestructive testing,biomedicine,radar,communication,military,national safty,aviation and other fields.The wide application of terahertz technology makes people have a stronger demand for terahertz devices.Among them,terahertz phase polarization modulator and detector have been deeply studied by researchers.Because the polarization state of light is closely related to the detection of material properties and the information carried by electromagnetic waves,it has become the research fore in recent years.However,due to the limitation of structure,the modulation of polarized light can only achieve one polarization state and can only work in the narrow band range.However,to realize multi polarization modulation or broadband work through the change of structure,there will be some problems,such as complex experimental preparation and difficult operation.For the detector,the detector based on the field effect principle has higher performance than the thermal effect,such as high response,low noise and so on.Therefore,it is pressing to develop terahertz polarization modulator and high-performance detector which integrates tunable,broadband and multi polarization modulation.Aiming at the above problems,using the characteristics of graphene plasmon resonance in terahertz tunable and field effect devices,this thesis introduces graphene plasmon into the research of terahertz polarization phase modulator and detector.The research work and main progress are as follows:(1)Using FDTD solutions simulation method and Maxwell equations and boundary conditions,the modulation of terahertz light polarization state by single-layer graphene metasurface is realized,and the analytical relationship between graphene resonance frequency and structural parameters of graphene metasurface is studied.The modulation effect from linear polarization(LP)to circular polarization(CP)is obtained,and the theoretical analytical relationship is successfully obtained.The results reveal that when graphene plasmon resonance occurs on the single-layer graphene super surface,the phase difference can reach 90°,so as to realize the modulation from linear polarization to circular polarization.In addition,the relationship between graphene resonance frequency and material structure is obtained for the first time to provide a theoretical basis for the design of structure:(?)#12(2)Using the simulation method of double-layer graphene plasmon resonance,the multi-polarization modulation in the wide range is realized,and also the influence of Fermi level on the polarization state modulation effect is studied.The results reveal that by adjusting the Fermi level of graphene in different layers and changing the resonance frequency of graphene plasmon,the polarization conversion can be realized at a wide frequency,and the phase difference caused by graphene plasmon resonance at different frequencies is calculated.The regulation results of multi polarization state in a wide frequency range are obtained for the first time,reaching a higher level in the field.At the same time,when the structure is fixed,by adjusting the value of the Fermi level of graphene,and by adjusting the Fermi level of two layers of graphene respectively,the modulation effect of multi polarization state conversion at the same frequency and different frequencies is realized.(3)The terahertz detector and metasurface were prepared by mechanical stripping,dry transfer graphene and wet transfer chemical vapor deposition(CVD)graphene,and their electrical properties were measured and researched.The results reveal that graphene with mechanical stripping and dry transfer on silicon substrate and graphene grown by CVD are prepared.Through the electrical test of transfer curve and output curve,graphene with mobility of 364 cm2/(V·s)and 2000 cm2/(V·s)are obtained respectively.