Research On Tunable Terahertz Metamaterials Absorber Based On Photosensitive Semiconductors

Metamaterial（MM）is a kind of specially designed artificial composite electromagnetic material,which has the electromagnetic properties that the conventional materials in nature do not have.As one of the branches of metamaterial applications,metamaterial absorbers（MMA）can be widely used in electromagnetic stealth,refractive index sensing,thermal imaging and other fields.Since the MMA was proposed,it has been developed from single-band to multi-band and even broadband.The operating frequencies also covers microwave,terahertz,infrared and visible ranges.The frequency band and amplitude of the tunable MMA can be controlled by the external excitation conditions,which can be applied to more abundant scenes,so it has become the research hotspot of the absorberThe methods to realize the tunable MMA is usually to integrated diodes,vanadium dioxide（VO₂）,graphene,photosensitive semiconductors,and other devices or materials in the unit structure that can be regulated by external excitation conditions.Since terahertz wave has the advantages of high resolution,large capacity and fast speed,terahertz devices have attracted much attention.In this paper,two kinds of tunable terahertz MMA are designed based on the optical-controlled characteristics of photosensor semiconductor.One is a single-/dual-band tunable MMA,and the other is a multi-state tunable MMA,which realizes the tunable absorption characteristics of single-/dual-band and single-/dual-/triple-band in terahertz range,and its absorption principle and the characteristic are researched in theory.The main contents are as follows:1.A single-/dual-band tunable MMA based on photosensitive germanium（Ge）is designed.The conductivity of the photosensitive Ge can be adjusted by adjusting the intensity of the pump beam so that it can be converted between the insulating state and the metallic state.The MMA has two nearly perfect absorption peaks at 0.89 THz and 2.37 THz when the Ge is in the insulating state,and an absorption peak of 99.7%at 1.10 THz when the Ge is in the metallic state.By analyzing the surface current distribution of the resonant frequencies,the absorption mechanism of the MMA is explained.Finally,the effects of incident and polarization angle on the characteristics of the MMA are studied.2.Based on the photosensitive semiconductor Ge and gallium arsenide（Ga As）,the photosensitive semiconductor Ga As is used as optical switch to design a photosensitive single-/dual band tunable MMA.On this basis,by extending the structure and introducing a second photosensitive semiconductor Ge,the second optical-controlled triple-band tunable MMA is proposed by using pump light of different wavelengths to regulate the conductivity of Ge and Ga As.When neither Ge nor Ga As is on,the structure can realize absorption in the triple-band.Dual-band absorption can be achieved when only Ge is on.Single band absorption can be achieved when both Ge and Ga As are on.Thus,the absorption characteristics of arbitrary switching of single-/dual-/triple-band absorption states are realized.The absorption mechanism of the MMA are explained by the surface current distribution.Simulation results show that the designed MMA has good polarization insensitivity and wide angle incidence characteristics.