Research On Design Of Perfect Absorbers And Slow Light Devices Based On Metamaterials

Metamaterial refers to a material with a periodic artificial structure having special physical properties such as a negative refractive index.By customizing the periodic structure in the metamaterial,the metamaterial can have some special physical properties that are not available in conventional materials.This idea of customizing the properties of the material by changing the size of the periodic man-made structure in the material expands the understanding of the material.Based on the concept of metamaterials,various functional devices can be designed.For example:perfect absorber,polarization converter,phase retarder,etc.The metamaterial perfect absorber belongs to the amplitude modulator in the metamaterials.When the electromagnetic wave is incident on the perfect absorber,the intensity of the reflected electromagnetic wave and the transmitted electromagnetic wave are both 0,which means that the electromagnetic wave is completely absorbed by the material.With this feature,the metamaterial perfect absorber can be used in the military field,such as the use of a metamaterial covered fuselage to achieve the stealth function of the radar.Compared to traditional absorbing devices,metamaterial perfect absorbers have many advantages,such as thin thickness,high stability,and customizable design.In actual use,whether it can be actively regulated becomes a key factor for the wide application of the perfect absorber.Achieving the ability to actively regulate the broad absorption of broadband metamaterials remains a challenge.The terahertz wave is an electromagnetic wave in a specific frequency range(0.1 THz-10 THz)in the electromagnetic spectrum.The infrared band with a frequency higher than the terahertz wave and the microwave band with a frequency lower than the terahertz wave have been extensively studied.However,due to technical reasons,the lack of efficient terahertz sources and corresponding terahertz detectors has limited the research of terahertz technology.With the advancement of ultrafast laser technology,the development of corresponding terahertz sources and detectors,electromagnetic waves in the terahertz band have also received attention.However,the lack of active regulation devices in the terahertz band is one of the key factors limiting the further development of terahertz technology.The development of actively regulated metamaterial devices provides an excellent solution for terahertz regulatory devices.This thesis mainly studies the active regulation of metamaterials.Firstly,the research on the design of metamaterial perfect absorbers is carried out.Two novel active metamaterial absorber structures are proposed,and their absorbing properties are studied by simulation.In the aspect of terahertz metamaterial devices,a group speed control device with active regulation of terahertz band is designed.The speed regulation performance of terahertz group is studied by experiments and simulations.The specific research work of this thesis is as follows1.An actively tunable switchable broadband perfect absorber is proposed.This perfect absorber has the function of switching between two wider frequency bands when temperature changed.In order to achieve this function,we added a phase change material vanadium dioxide in the traditional perfect absorber By the structural design,the absorber has different effective structures above the phase transition temperature and the phase transition temperature,thus achieving the switching function.We verified the absorption performance of the perfect absorber by simulation,and explored the absorption mechanism of the perfect absorber by the effective medium theory.2.An actively tunable double-band perfect absorber based on graphene-dielectric multilayer structure is proposed.Absorber with this structure has two absorption peaks,and the absorption peak position can be regulated by adj usting the graphene Fermi level by a gate voltage.By analyzing the surface plasmons in the graphene-dielectric multilayer structure,we explored the physical mechanism of this structure with two absorption peaks.At the same time,according to the dispersion relation in the graphene-dielectric multilayer structure,an empirical formula for calculating the position of the absorption peak through the graphene Fermi level and structural geometric parameters is derived.The reliability of the empirical formula is verified by comparing the position of the absorption peak obtained by the simulation with the position of the absorption peak calculated by the empirical formula.3.An electromagnetic induced transparent(EIT)device with ultra-fast regulation of the terahertz wave group velocity delay is designed.In order to achieve ultra-fast regulation of group velocity,we introduce P+ ion-implanted Si structure in the traditional EIT metasurface.Due to the large number of defects in the ion-implanted Si,the photo-generated carriers in Si can be quickly recombined.We first studied the performance of the metasurface by simulation,and then fabricated the sample by micro-nano processing,and tested the sample by optical pumped terahertz detection(OPTP)system.Through the analysis of the experiment results,The performance of the sample on group velocity regulation was obtained.We also fit the experiment results by a coupled oscillator model to further illustrate the physical mechanism of regulation.