Research On Tunable Optoelectronic Devices Based On Graphene/Metal Nanostructure

As a special two-dimensional material,graphene has many excellent physical properties.Researches on graphene and its combination with micro-nano photonics have attracted more and more attentions in recent years,such as graphene-based high-efficiency absorbers,polarization converters,optical modulators and other devices.Graphene has strong light absorption effect in visible light,and it can excite surface plasmonic polaritons in mid-infrared and terahertz wavebands.Meanwhile,the Fermi level of graphene can be changed by chemical doping or electrical control,which means that the conductivity of graphene can be changed in real time.In this thesis,graphene-based nano optoelectronic devices,including mid-infrared absorbers,polarization controllers,and near-infrared light modulators/optical switches are investigated.The main contents of the thesis are as follows:(1)A tunable absorber in the mid-infrared band is proposed.By designing a graphene grating strip,the surface plasmon polaritons of the graphene are excited.The interaction between graphene and incident light is enhanced by the microcavity formed by a graphene grating and a metallic film.Meanwhile,by changing the Fermi level of graphene,the wavelength of absorption can be tuned in the mid-infrared band.(2)A mid-infrared polarization controller is proposed.By designing a metal grating/graphene hybrid structure,the resonant frequency of the localized surface plasmonic polaritons of metal grating can be changed by changing the conductivity of the graphene,so that the phase difference and amplitude ratio of the reflected light in the two orthogonal directions can be changed in real time.Therefore,optoelectric devices that can change the polarization state of the reflected light in real time can be obtained with a single structure.(3)A near-infrared light modulator/optical switch based on graphene and metallic nanostructure in optical communication waveband is proposed.A multilayer graphene and microcavity structure are employed to enhance the interaction between the metal gratings and graphene.By changing the Fermi level of graphene,the reflectivity of the incident light can be changed so that tunable light modulator and optical switch at the wavelength of 1550 nm can be achieved.Furthermore,by changing the structural parameters of the device,a wideband optical switch from 1400 nm to 1700 nm can be obtained,and the optimized grating structure also greatly improves the tolerance of the fabrication.Finally,a two-dimensional nanostructure was designed,and a polarization-independent optical switch in a broadband wavelength range of 1400nm-1700 nm was achieved.(4)Experimental fabrication of the designed wideband(1400nm-1700nm)optical switch is conducted.Metal and dielectric films were prepared by electron beam evaporation and ion beam sputtering,respectively.Graphene thin films were prepared by chemical vapor deposition(CVD),and were transferred to the multi-layer structural device in wet way.Metal grating was prepared through ion beam etching(FIB),and a preliminary device sample was obtained and tested.