Design On Optically And Electrically Controlled THz Metamaterial And Theoretical Simulation On THz Wave Transmission

Terahertz(THz)science and technology has aroused extensive attention in the science community around the world owing to its potential applications in various cutting-edge technologies.With the development of THz science and technology,various functional devices working in terahertz regime are becoming more and more important.The materials that can control THz wave in nature are expensive and scarce,which leads to the lack of modulators in terahertz regime and also limits the development of terahertz technology.The rise of artificial metamaterials brings new opportunities for THz technology moving towards mature applications.Special electromagnetic properties that do not process in a natural material can be realized in metamaterials by means of reasonable structure design and material selection,which provides alternative ways for realization of boh active and passive control of THz wave.In recent years,metamaterials in THz regime have developed rapidly,a large number of new structures with deisred functionanlities have been designed and developed.Among them,those metamaterials with actively regulatable functions and properties are particularly attractive,which have become a new research hotspot in THz communicity due to their flexibility and controllability.These new designs also provide a new view for developing active device for future THz optical communications.Active metamaterials are structures whose electromagnetic response can be regulated by using special materials or applying external stimuli.It can be roughly divided into the following several types:semiconductor metamaterials based on optical control and electronic control,graphene,non-linear,temperature-controlled,photonic and liquid crystals,etc.Among them,the semiconductor and graphene based metamaterials with optical and electronic control have been developed most rapidly because of their simple operation,stable performance and low experimental costs.In this dissertation,the tunable metamaterial working in THz regime are designed and studied with theoretical simulation,the main contents and innovative points are summarized as follows:1)An active THz metamaterial with the functionality of enhancing and localizing the electromagnetic field of the incident pulse based on optical control is proposed(SLE metamaterial),the metamaterial is a composite structure consisting of metal-gallium arsenide-metal and takes the shape of diabolo.As the core element of the metamaterial,Ga As gap can be swithced between insulating and conducting states with the incident femtosecond laser pulse on and off.This enables the metallic parts of SLE metamaterials to switch from the state of mutual insulation to the electrical connection in real time.Consequently,the local enhancement of the SLE metamaterial can be switched between the two modes of electric field enhancement and magnetic field synergistic enhancement.Numerical simulations demonstrate that the intensity of incident wave can be enhanced by two orders of magnitude in the area of1?m~2 by utilizing the SLE metamaterial.The physical mechanism of field enhancement originated from SLE metamaterial is reasonably explained based on the surface plasmon theory.2)A graphene-based independently tunable dual-band plasmon induced transparency metamaterial in terahertz regime(DBPIT metamaterial)is proposed.The unit cell of the DBPIT material is consisted of a diabolo-like bright mode resonantor and two split ring resonator(SRR)with different sizes distributed on both sides of the bright mode.Two pronounced transparency windows are obtained in the transmission spectrum arising from the near-field coupling between the bright and dark mode resonators.The numerical simulations indicate that not only the resonance frequency but also the transmission amplitude can be independently tuned by manipulating the Fermi level in graphene of the individual resonators via gate voltage.The classical three-oscillator model is used to characterized and analyzed the DBPIT behavior,and the physical mechanism of DBPIT metamaterials is reasonably explained.It is worth mentioning that the the diabolo-like structure has additional ability to enhance the transmission of transparency windows.3)A dual-band plasmon induced transparency scheme based on bright mode control enbled by an all-metal metamaterial is proposed.The magnetic field enhancement effect can be adjusted by modifying the geometry of the bright mode resonator,and then effecting the magnetic response of the dark mode resonators in the near-field coupling process with the bright mode,consequently the purpose of adjusting the dual-band plasmon induced transparency is achieved by this means.Compared with the existed schemes,the advantages of this scheme lie in:the regulation process of PIT is based on the bright mode rather than the dark one of the system;the regulation process is mainly based on the magnetic response between the bright and dark modes of metamaterials rather than the corresponding electric field one.This scheme is helpful in the study of tunable plasmon induced transparency.