Study On Filtering Characteristics Of Metasurface Structures Based On Temperature-controlled Phase Change Materials

Metasurface is a new kind of artificial electromagnetic material with sub-wavelength size,which has extraordinary and unique electromagnetic characteristics.By designing its unit structure and material characteristics,it can realize flexible and efficient regulation of electromagnetic wave.Metasurface is small in size,easy to integrate and process,and has great application potential and wide application prospect in the field of electromagnetism and optics.Phase-change materials have phase-change characteristics and can switch between different phase states.By taking advantage of the huge differences in optical properties between different phase states,the problem that the performance of metasurface devices is fixed after fabrication is solved,and the metasurface has the tunability to realize the active regulation of electromagnetic waves,avoiding the uniformity of traditional regulation.In this thesis,phase change materials and metasurfaces are combined,and two kinds of metasurface filter switching devices with tunable performance are proposed for the infrared band,respectively for broadband and narrowband control.Considering that the material properties of phase change materials change more significantly in the infrared band,the design band selects the 3 μm～5 μm band in the infrared.The main research work is as follows:(1)In theory,the equivalent electrical parameters of the PCM were studied,the permittivity of GST was calculated in the required band,and the approximate relationship between temperature and crystallization rate was obtained by fitting,which provided a theoretical basis for the subsequent device design.(2)A broadband transmissive metasurface device based on phase change materials is proposed,and a broadband filter switch is realized.The influence of each structural parameter in the designed structure on the filtering characteristics of the metasurface is studied,and the structure is optimized.The optimized waveband range is 3.46 μm～4.66 μm,the bandwidth is 1.2 μm,and the modulation depth is above 70.8 %,which realizes the effect of broadband filtering,and the proposed structure is insensitive to the incident angle of electromagnetic waves from 0 ° to 60 °.The designed The structure has a large tolerance to the incident angle,and also has polarization insensitivity.In addition,the tunability of the metasurface of the phase change material is analyzed.In the broadband band range of 2.10μm～4.66 μm(bandwidth is 2.56 μm),the "on" and "off" filtering effect can be obtained at any wavelength of the band by changing the temperature to adjust the material properties of the GST,and the tunable filtering switch is realized.(3)A narrowband transmissive metasurface device based on phase-change materials is proposed to realize a narrowband filter switch.The influence of each structural parameter in the designed structure on the filtering characteristics of the metasurface is studied,and the structure is optimized.The narrowband is optimized to 3.8 μm,the modulation depth is more than 81.8%,and the quality factor is as high as 84.4.The effect of narrowband filtering is realized,and the proposed structure is insensitive to the incidence angle of electromagnetic wave from 0 ° to 30 ° and the polarization angle of lectromagnetic wave from 0 ° to 40 °.In addition,the tunability of the metasurface of phase change materials is also analyzed,and it is found that with the deepening of the crystallization degree,a continuously tunable narrowband filter switch in the range of 3.00 μm～3.80 μm is realized.