Abstract：Terahertz(THz) electromagnetic radiation lies between the microwave and far-infrared regions and has attracted much attention due to its wide application. However, due to the lack of terahertz functional devices, it can not fully meet the need of practical applications, so the modular and other terahertz functional devices needs to make a breakthrough. This paper mainly studies the terahertz wave modulator using the transmission terahertz spectral system. Metamaterial can be applied to the absorber. However, when the structural parameters of the metamaterial are once determined, the perfect absorption can only be generated at a specific resonance frequency. We designed three composite metamaterials structures to explore the resonance of composite metamaterials; three structures are a single gap of a metal resonance ring, a single gap of a metal resonance box and asymmetric double gaps of a metal resonance box; in the gap of three structures with photosensitive material indium oxide. We change the conductivity of indium oxide, explore terahertz modulation properties of these composite metamaterial structures and do numerical simulations of the electric field distribution of different resonance frequencies for three structured THz frequency switches. For a single gap of different shapes of the metal resonant rings, the resonance frequency is different, but with the increasing of indium oxide's conductivity, resonance peak absorption intensity gradually decreases. From the corresponding electric-field distribution diagram, with the increasing of indium oxide's conductivity, the gap edge electric field strength is increasingly weak, so the resonance peak absorption strength is more and more weak. This process can be considered a terahertz wave in the resonance frequency dynamic switch. For asymmetric double gaps metal resonance box, we deviate from the gap in the middle to fill the indium oxide; the structure's frequency spectrogram shows two resonance peaks. With the increase of conductivity, a resonance peak absorption strength gradually weakens and the other resonance peak absorption strength doesn't change significantly. Thus, the resonance peak whose absorption strength weakens with the increase conductivity is Fano resonance, and the other resonance peak whose absorption strength does not change significantly is dipole resonance. As can be seen from the corresponding electric-field distribution diagram, the energy of the incoming THz wave of the Fano resonance is mainly concentrated on the right metal arm of the metal resonance box, and as the conductivity increases, the quantity of charges accumulated at the gap of the right metal arm is increasing. In contrast, the energy of the dipole resonance incoming THz wave is mainly concentrated on the left metal arm of the metal resonance box and as the conductivity increasing, the electric-field distribution of the dipole resonance does not change significantly.
Key words：Terahertz; Frequency switch; Metamaterial
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