Abstract-Terahertz absorber with dynamically switchable dual-broadband based on a hybrid metamaterial with vanadium dioxide and graphene

 

Yan Liu, Rui Huang, Zhengbiao Ouyang, 

(a) Schematic of the proposed absorber based on VO2-graphene metamaterials and the incident light polarization configuration. (b) Top view of the unit cell. (c) Side view of the unit cell.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-13-20839&id=452098

An absorber based on hybrid metamaterial with vanadium dioxide and graphene has been proposed to achieve dynamically switchable dual-broadband absorption property in the terahertz regime. Due to the phase transition of vanadium dioxide and the electrical tunable property of graphene, the dynamically switchable dual-broadband absorption property is implemented. When the vanadium dioxide is in the metallic phase, the Fermi energy level of graphene is set as zero simultaneously, the high-frequency broadband from 2.05 THz to 4.30 THz can be achieved with the absorptance more than 90%. The tunable absorptance can be realized through thermal control on the conductivity of the vanadium dioxide. The proposed device acts as a low-frequency broadband absorber if the vanadium dioxide is in the insulating phase, for which the Fermi energy level of graphene varies from to 0.1 eV to 0.7 eV. The low-frequency broadband possesses high absorptance which is maintained above 90% from 1.10 THz to 2.30 THz. The absorption intensity can be continuously adjusted from 5.2% to 99.8% by electrically controlling the Fermi energy level of graphene. The absorption window can be further broadened by adjusting the geometrical parameters. Furthermore, the influence of incidence angle on the absorption spectra has been investigated. The proposed absorber has potential applications in the terahertz regime, such as filtering, sensing, cloaking objects, and switches.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Actively tunable bi-functional metamirror in a terahertz band

 

Kun Zhang, Yan Liu, Shixia Li, Feng Xia, Weijin Kong, 

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-46-3-464

In this work, we have proposed an actively tunable bi-functional metamirror based on a bi-layer graphene structure. The metamirror acts as a spin-selective absorber under circularly polarized incidence, which behaves as nearly perfect absorption and reflection for right and left circularly polarized waves, respectively, leading to giant circular dichroism. On the other hand, it is a polarization converter under linearly polarized incidence, which reflects the linearly polarized wave into a left circularly polarized wave. Both the spin-selective absorber and the polarization converter can be actively switched between ON and OFF states, with the working frequency controlled by the voltages applied to graphene. Moreover, the metamirror is insensitive to the incidence angle, which contributes to its application as a stable single-mode spin-selective absorber and polarization converter. This bi-layer graphene structure offers a method to construct actively tunable bi-functional metamirrors, which may achieve potential applications in integrated devices, such as active spin detectors, absorbers, and quarter-wave plates for terahertz waves.

© 2021 Optical Society of America

Abstract-Emission of terahertz plasmons from driven electrons in grated graphene

Chengxiang Zhao, Yan Liu, Yuan Qie, Fangwei Han, Hu Yang, and Haiming Dong

 (a) Plasmon emission distribution in the direction of 𝜃=0∘$\theta =0^{\circ }$ for different driving electric fields at a fixed grating period and electron density. The drifting electron velocity v𝑥${}_x$ and temperature T𝑒${}_e$ for the driving electric fields of 15 kV/cm, 10 kV/cm, 5.0 kV/cm, 1.0 kV/cm, and 0.2 kV/cm are, respectively, 1.76×$\times$107${}^7$ cm/s, 1.49×$\times$107${}^7$ cm/s, 1.06×$\times$107${}^7$ cm/s, 3.35×$\times$106${}^6$ cm/s, and 0.72×$\times$106${}^6$ cm/s, at 712.01 K, 602.70K, 474.78 K, 324.25 K, and 301.26 K. (b)-(d) Angular and frequency dependence of plasmon emission for different electric fields 𝐹𝑥=15, 10$F_x=15,10$ and 5.0$5.0$ kV/cm at a fixed electron density 𝑛𝑒=1.0×1012$n_e=1.0\times {10}^{12}$ cm−2${}^{-2}$.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-19-26569

Terahertz plasmon emission is the key to getting terahertz radiation, which has resulted in numerous studies on it. In this paper, we present the results of a theoretical investigation of terahertz plasmon emission by drifting electrons in a grated graphene system driven by an electric field by applying the Boltzmann’s equilibrium equation method. The results show that plasmon frequencies from terahertz to infrared are generated by drifting electrons through the interaction between plasmons and electrons. Obvious increase of the plasmon emission strength with the driving electric field can be seen when the electric field is more than a certain strength (e.g. 1.0 kV/cm). The effects of electron density and the grating period on the emission strength of plasmons were also investigated. It was found that terahertz plasmons can be obtained by applying a grating with appropriate period. The plasmon frequencies can be tuned using either the driving electric field or the electron density controlled by the gate voltage or the grating parameters. This work may help to gain insight into graphene plasmonics and be pertinent to the application of graphene-based structures as electrically tunable terahertz plasmonic devices.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement