Research On Tunable Fano Resonance Metasurface Based On Plasma-filled

Fano resonances are widely applied in microwave,optics and terahertz regions because of its asymmetric line shape resulting from the interference between a discrete narrow spectrum and a continuous broaden spectrum.The Fano resonances based on the alldielectric and metal surface plasmon polariton structures present greatly attractive properties.For instance,the frequencies offset of the Fano peak or dip can be controlled independently.The tunable Fano resonances achieved through changing geometric parameters are called passive tuning,and it has a disadvantage of little adjustable degree of freedom.Plasma is a kind of dispersion material whose relative dielectric constant is affected by the frequency of an incident electromagnetic wave and the plasma density.Compared with the photonic crystals,the plasma photonic crystals own an especial advantage that the photonic bandgap can be adjusted actively.This thesis was accomplished based on numerical simulation of finite element method.Firstly,the photonic bandgap and the tunability of one-dimension plasma photonic crystal are studied.Then,the Fano resonance is obtained from the plasmafilled one-dimension superlattice array and we further studied the effect of geometric parameters and plasma density on the frequency of Fano resonance.Simultaneously,the principal of the generation of Fano resonance is explained theoretically.The main results and innovations are as follow:The transmission properties and photonic band diagrams of one-dimension plasma photonic crystal with or without defect were studied and we had analyzed the influence of plasma density on photonic bandgap.The results of research demonstrate that the number,center frequency,width and depth of bandgaps are affected by plasma density.For the structure with a point defect,the frequencies and transmittance of defect mode are depended on plasma density.Contrasting with the transmission spectrums and photonic band diagrams,it is clear that the frequencies when transmittance is zero correspond to forbidden bands.The conduction bands appear in the forbidden bands of the structure with a point defect,which corresponds to the frequency of defect modes.At the same time,the influences of plasma density on photonic bandgap of TE and TM modes were studied.The tunable Fano resonances obtained from the plasma-filled one-dimension superlattice array are studied.The transmittance spectrums and photonic band diagrams of superlattice array and the Mie scattering and radar cross section of an isolated plasma cylinder were analyzed.The results show that the Fano resonance was generated from the destructive interference between Mie scattering and Bragg scattering.The resonance frequencies of Mie and Fano resonances are corresponding a dispersionless band in photonic band diagram.The active reconfiguration and tunability of Fano resonance were investigated.In addition,the influence of the radius of plasma cylinder and the thickness of quartz tube on Fano resonance,Mie scattering and radar cross section were studied also.The boundary condition method was introduced to explain the cause of the existence of frequency difference between Mie and Fano resonances.Moreover,the influences of collision frequency of plasma on transmittance spectrum of superlattice array,Fano line shape and experimental results were researched.A one-dimensional silver nanograting structure was used to verify whether Fano resonance still occurs when the perfect lattice is converted to superlattice The results demonstrated that the Fano resonances do generate when the perfect lattice is transformed to superlattice.When a dielectric layer is added on the top of each silver grating of the perfect lattice,the Fano resonance will also occur.By using a suitable material,tunable Fano resonance in the visible to near-infrared wavelength range and tuning from single Fano to multiple Fano can be achieved.