Abstract-Graphene-Assisted Narrow Bandwidth Dual-Band Tunable Terahertz Metamaterial Absorber

Dexian Yan,  Miao Meng,  Jiusheng Li, Xiangjun Li
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https://www.frontiersin.org/articles/10.3389/fphy.2020.00306/full

A tunable graphene terahertz metamaterial absorber is designed by treating a monolayer continuous dumbbell-shaped structure graphene layer, which can simultaneously realize the narrow bandwidth and dual-band absorption with transverse magnetic (TM) polarization and wide incident angle operation. Two pronounced absorption peaks are caused by the novel toroidal dipole phenomenon and magnetic plasmon polariton. By optimizing the geometry parameters, the relative narrow bandwidths of the two absorption peaks are 26.4 and 23.5 GHz at frequencies of 0.2242 THz and 0.5302 THz, respectively, with the absorption rate above 99.6%. Since the continuous dumbbell-shaped graphene structure is treated in the absorber, a more convenient way to realize the tuning ability by treating a bias voltage compared to the absorbers with discrete graphene structures. The designed device can work at a wide incident angles (up to 80°) under TM polarization with the absorption above 88% at low frequency. The simulation results are basically in good agreement with the results of the equivalent circuit model. This work offers huge potential applications in terahertz imaging, detecting and sensing, especially in the 6G communication systems.

Abstract-Tuning control of dual-band terahertz perfect absorber based on graphene single layer

Dexian Yan, Jiusheng Li

https://iopscience.iop.org/article/10.1088/1555-6611/ab05bd/pdf

A dual-band graphene tunable terahertz metamaterial absorber is designed and numerically analyzed in this paper. The tunable absorber consists of two sizes of graphene square rings and a copper strip layer separated by a silicon dielectric layer in a unit cell. The simulation results demonstrate that the absorption performance of the terahertz absorber can be achieved by combining the absorption peaks induced by different graphene square rings. The absorber can achieve the absorption peaks of 99.8% and 99.9% at 0.74 THz and 1.71 THz, respectively. By changing the Fermi energy E F of the graphene material through modulating the bias voltage, the absorption and spectral position of the proposed absorber can be tuned. The flexible and easy design of the proposed single-layer graphene absorber makes it easier to be used in various metamaterial applications including sensing, imaging and communication.

Abstract-Light-controlled tunable terahertz filters based on photoresponsive liquid crystals

Dexian Yan, Jiusheng Li, and Lufan Jin

http://iopscience.iop.org/article/10.1088/1555-6611/aaf326

We theoretically propose and investigate a light-controllable narrow-band terahertz (THz) filter and a dual-wavelength filter employing a square lattice photonic crystal with point and line defects. The point defects filled the photoresponsive liquid crystal. The change of the refractive index of the liquid crystal mixture material caused by the linearly polarized ultraviolet (UV) light and visible light results in a shift of the resonant wavelength of the cavity in the filter. We calculate transmittance spectra for the proposed THz wave filters, which have a full width at half maximum of 10 GHz and a transmittance of 95% at the resonant frequencies. By changing the polarized directions of UV and visible light, the performance characteristics of the filters can be adjusted.

Abstract-Design and analysis of the influence of cladding tubes on novel THz waveguide

Dexian Yan, Jiusheng Li



https://www.sciencedirect.com/science/article/pii/S0030402618319314

A novel terahertz (THz) waveguide was theoretically designed based on polymethylmethacrylate (PMMA) negative curvature fiber. The confinement loss decreased 3.5 times when there were optimum gaps between adjacent cladding tubes of the fibers with six tubes. Confinement loss as low as 0.08 dB/cm and transmission bandwidth of 700 GHz were obtained when the tube wall thickness and gap range of the fiber were 40 μm and 357–416.5 μm, respectively, and the power ratio of the proposed fiber was as high as 99%. When the fiber had six surrounding tubes, the optimum gap was 6 times larger than the optimum gaps in fibers composed of eight or ten surrounding tubes. The PMMA negative curvature fibers with a broad range of gap made it well-suited for THz transmission with low confinement loss and wide bandwidth.