Research On The Control Properties Of Terahertz Waves Based On All-dielectric Metamaterials

Terahertz(THz)waves are electromagnetic waves located between the microwave and infrared spectrum,which have unique propagation characteristics of low photon energy,large bandwidth,and high carrier frequency,showing broad application prospects in many practical fields,such as communication,imaging,biomedicine,and astronomical research.Nevertheless,there is a challenge to find natural materials that respond strongly to THz waves,thus the development of high-performance THz functional devices still faces great challenges.Composed of subwavelength unit cells,metamaterials(MMs)offer a useful approach for solving this problem.Regretfully,plagued by Ohmic loss and radiation loss,the Q-factors of MMs devices are very low which seriously limits the performance of THz functional devices.All-dielectric metamaterials(ADMs)have the advantages of low loss,high transmittance,and good semiconductor process compatibility.By utilizing the grapheme and strontium titanate(STO)as the tunable medium,we designed and investigated the THz functional devices with fine performances based on ADMs structures.The main contents and results are summarized in the following.(1)Based on the ADMs with Si-Si O₂ nested composite microstructure,the Fano resonance spectrum with a Q-factor of more than 270 is obtained by breaking the symmetry of the structure.When the asymmetry?varies in the range of 2–10?m,the amplitude modulation depth(MD)of the Fano resonance is up to 75%.In addition,the tunable of Fano resonance is achieved by regulating the Fermi level of graphene,e.g.when the Fermi level increases from 0.01 e V to 0.3 e V,the frequency MD of Fano resonance is about 20%.(2)Based on the periodically arranged dielectric sphere-spacer layer-strontium titanate substrate structure,the tunable propagation properties of THz ADM absorber have been investigated,including the effects of microstructure configuration,external temperature,and graphene Fermi level.With the results,we demonstrated that temperature control and electrical control are both effective methods to achieve THz wave modulation.For example,when the unit structure is a tight arrangement of 2?2strontium titanate spherical shells,a frequency modulation depth of 62%can be obtained in the temperature range of 77-400 K.In addition,by biasing the voltage to increase the Fermi level of graphene from 0.1 e V to 1.0 e V,the absorptivity can be increased from 0.8352 to 0.9953 and the absorption frequency was shifted from 0.8604THz to 1.122 THz.