Research On The Color And Absorption Characteristics Of Resonant Periodic Metasurface Structures

The phase,polarization,and amplitude of electromagnetic waves can be controlled flexibly by metasurface structures,which make them manipulate light on the nanometer scale.Plasmon metasurface structure and dielectric metasurface structure based on high refractive index materialsare are two basic structures that are widely used in biomedicine,display imaging,optical lens,solar cell,surface enhanced Raman scattering（SERS）and so on.By optimizing the metasurface structure,a series of strange electromagnetic responses can be achieved,such as the optical properties of perfect absorber and structural color.Different from traditional absorbers,the metasurface structures with perfect absorbers achieve both the characteristics of lightweight and miniaturization while considering the perfect absorption characteristics.So,the structures satisfied the development trend of optical devices.Traditional color dyes are difficult to adapt to harsh environment,and some even cause environmental pollution or induce cancer.The metasurface structure can realize full-tone modulation in the visible range.This structure color has the advantages of high resolution and good stability.Therefore,the reasonable design of metasurface structure will broaden its application and play an important role in scientific research.This thesis focuses on the characteristics of plasmon metasurface structure and high refractive index dielectric material metasurface structure in absorber and structure color.Relevant research routes can be roughly divided into material selection,structure design,parameter optimization,spectral characteristics,and mechanism analysis.The main contents include:（1）A kind of perfect absorber with adjustable single and double peaks in visible light band is designed by using the traditional metal-Insulator-metal（MIM）metasurface structure.The design and simulation setup of MIM nanoblock structure are described in detail.The absorber is composed of Ag nanoblock,SiO₂nanoblock and thick Ag layer.The effects of structural parameters such as the thickness of the upper Ag nanoblock,the thickness of the middle SiO₂nanoblock and the side length of the nanoblock on the absorption spectrum were investigated respectively.By fixing the duty cycle and changing the side length of the nanoblock,the following results can be obtained:the peak position at 450nm is fixed,and the peak position can be manually adjusted in the range of 500nm-700nm.The physical mechanism of the two absorption peaks is determined by theoretical calculation and simulation.The absorption peak of short wavelength is supported by surface plasmon mode resonance,and the long wavelength absorption peak is supported by cavity resonance mode.With the increase of the thickness of the intermediate insulator layer,the mode splitting phenomenon can selectively control the appearance of the two absorption peaks.（2）A perfect absorber of IMIM nanoblock structure working in visible to near-infrared band is proposed.The design and simulation setup of IMIM nanoblock structure are described in detail.The absorber is composed of SiO₂nanoblock,Ag nanoblock,SiO₂nanoblock and thick Ag layer.The influence of thickness ratio of Ag nanoblock and lower SiO₂nanoblock on absorption spectrum was investigated,and the sensitivity of absorption spectrum to incident angle,polarization state and background refractive index was also investigated.The absorption peak at the short wavelength position is mainly supported by the SPP mode excited by the interface of the upper SiO₂/Ag nanoblock.The absorption peak at the long wavelength position is first supported by the cavity resonance mode,but with the increase of the thickness ratio of Ag nanoblock and SiO₂nanoblock,the absorption peak is supported by the SPP coupling mode at the upper and lower interfaces,that is,the phenomenon that the absorption peak shifts from blue to red is realized.Within the range of design parameters,two positions with different structural parameters but completely identical absorption peaks can be found,and there are"on"and"off"characteristics at the peak positions of short-wave absorption peaks.This property can be applied to optical switches in optical circuits,and provides a new idea for plasma sensors.It has broad application prospects in the fields of filtering and imaging.（3）A method to suppress the high-order Mie resonance excited by high refractive index medium HfO₂is proposed,which is to build a single SiO₂matching layer on the HfO₂grating analogue structure.The design and simulation setup of double-layer all-dielectric grating analogue are described in detail,and the influence of the geometric parameters of SiO₂structure on the reflection spectrum is explored.The magnetic dipole resonance excited by the cyclic displacement current results in the magnetic field being confined to the high refractive index material HfO₂.On the premise of maintaining the resonance peak intensity,the double-layer all-dielectric grating analogue structure effectively suppresses the excitation of higher-order Mie resonance through the upper SiO₂structure,and the non-resonant position is almost completely transparent（T>99%）.The distribution of chromaticity coordinates on CIE1931 chromaticity diagram also proves that suppressing side peaks can effectively improve the saturation of structure color,which is crucial for high-end imaging equipment.Narrow bandwidth（～1.51nm）and high-quality factor（～424.5）reflection characteristics can be obtained by adjusting the duty cycle of the structure.This work is of great significance for the applications of sensors,optical displays,imaging,data storage and color filters.（4）Based on the relevant research of SiO₂-HfO₂all-dielectric grating analogue structure to improve the quality of structural color,the idea of equivalent refractive index is further introduced to replace the SiO₂matching layer with HfO₂matching layer with the same equivalent refractive index.Compare the suppression effect of HfO₂,SiO₂-HfO₂and HfO₂-HfO₂on the higher-order Mie resonance mode.The chromaticity coordinates of the three structures are calculated and plotted on CIE1931 chromaticity diagram.The quality of the structural colors obtained by the three structures is in sharp contrast.This part of work further broadens the suppression methods of higher-order dipole modes,and injects new vitality into the applications of optical camouflage,anti-counterfeiting printing and other fields.