Currently, terahertz metamaterials are studied in many fields, but it is a major challenge for a metamaterial structure to perform multiple functions. This paper proposes and studies a switchable multifunctional multilayer terahertz metamaterial. Using the phase-transition properties of vanadium dioxide (VO2), metamaterials can be controlled to switch transmission and reflection. Transmissive metamaterials can produce an electromagnetically induced transparency-like (EIT-like) effect that can be turned on or off according to different polarization angles. The reflective metamaterial is divided into I-side and II-side by the middle continuous VO2 layer. The I-side metamaterials can realize linear-to-circular polarization conversion from 0.444 to 0.751 THz when the incident angle of the y-polarized wave is less than 30°. The II-side metamaterials can realize linear-to-linear polarization conversion from 0.668 to 0.942 THz when the incident angle of the y-polarized wave is less than 25°. Various functions can be switched freely by changing the conductivity of VO2 and the incident surface. This enables metamaterials to be used as highly sensitive sensors, optical switches, and polarization converters, which provides a new strategy for the design of composite functional metamaterials.
Electromagnetically induced transparency (EIT) is a quantum interference phenomenon in a three-level atomic system. The generation of quantum interference effect significantly reduces the light absorptivity of the specific frequency that is strongly absorbed, and produces a sharp " transmission window" in the resonance absorption region. EIT is usually accompanied by strong dispersion, which significantly reduces the group velocity of light and enhances the nonlinear interaction. The EIT phenomenon of atomic system usually needs to be observed at very low temperature or high intensity laser, which is a very serious challenge for the application of EIT technology. The simulation of electromagnetically induced transparency using metamaterials can effectively break through these limitations.<br>In this paper, an electromagnetically induced transparent-like terahertz metamaterial structure with three bright modes is proposed and investigated. Two weakly hybrid states are composed of two bright modes with similar resonant frequencies. The energy between the two oscillates back and forth, and a transparent window is generated between the two resonance points. The designed metamaterial is composed of two groups of bright modes with adjacent resonant frequencies, and two groups of bright modes are coupled to produce two transparent windows. The formation mechanism of electromagnetically induced transparency-like is analyzed based on the simulation curve and electric field distribution. In addition, sensing properties of metamaterials is determined by simulation and calculation, and the refractive index sensitivity of the two windows can be as high as 451.92 GHz / RIU and 545.31 GHz / RIU under the optimal thickness of the measured substances. Through the sensing simulation of six petroleum products, it is verified that the dual-band has higher advantages in dielectric constant matching than the single frequency band. The characteristics of the designed metamaterial in the slow light effect are also studied. The maximum group delay of the two windows can reach 9.98 ps and 6.23 ps. Therefore, the structure is considered to have important application value in the field of high sensitivity sensors and slow light devices.
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