Abstract-Dual-controlled switchable broadband terahertz absorber based on a graphene-vanadium dioxide metamaterial

Tongling Wang, Yuping Zhang, Huiyun Zhang, and Maoyong Cao

Schematic of graphene- and VO2-based metamaterial broadband absorber geometry. P = 15 µm, Lin = 3.8 µm, Lout = 6.8 µm, win = 0.5 µm, wout = 2 µm, d = 28 µm, and h = 0.7 µm.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-10-2-369

We propose a dual-controlled switchable broadband terahertz (THz) metamaterial absorber based on a hybrid of vanadium dioxide (VO2) and graphene that demonstrates strong polarization-independent characteristics and works well at a wide range of incidence angles. The peak absorptance of the proposed absorber can be tuned from 26 to 99.2% by changing the Fermi energy of the graphene; the absorptance can be dynamically tuned from 9 to 99.2% by adjusting the conductivity of the vanadium dioxide because of its unique insulator-to-metal transition characteristic. Using these two independent controls in tandem, we found that the state of the proposed absorber can be switched from absorption (>96%) to reflection (>73.5%), and the transmittance can be tuned from 0% to 65% while maintaining broad bandwidth (1.05-1.6 THz), resulting in a better-performing switchable broadband terahertz absorber. Furthermore, we have provided a discussion of the interference theory in which the physical mechanism of the absorption is explained from an optical point of view. The absorber achieves dual-controlled absorptance switching via two independently controllable pathways, offering a new method for switching and modulation of broadband THz radiation.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Controllable broadband asymmetric transmission of terahertz wave based on Dirac semimetals

Linlin Dai, Yuping Zhang, John F. O’Hara, and Huiyun Zhang

 (a) PCR of linearly polarized wave, (b) the current densities in the top and bottom layers of the x-polarized wave at 1.389 THz and 1.668 THz, respectively.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-24-35784

We present a dynamic metamaterial based on Dirac semimetals and capable of realizing broadband and tunable asymmetric transmission in the terahertz region. The Dirac semimetal resonators have a chiral structure patterned with double-T resonators that results in partial polarization conversion of waves incident upon the material, leading to asymmetric transmission across a wide frequency range. We show how the gradual shift of the semimetal Fermi energy permits a method of control over the asymmetric total transmission.

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

Abstract-Tunable plasmon-induced transparency in H-shaped Dirac semimetal metamaterial

Huan Chen, Huiyun Zhang, Xiaohan Guo, Shande Liu, and Yuping Zhang

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-4-752&origin=search

We present a numerical and theoretical study on the realization of tunable plasmon-induced transparency (PIT) effect at terahertz frequencies in Dirac semimetal (known as “three-dimensional graphene”) metamaterials. Simulations reveal that the PIT effect is generated by an electric field transferred from the central strip to side strips due to the structural symmetry breaking. The most prominent feature is that the plasmonic resonance in Dirac semimetals can be actively tuned by changing the Fermi energy and an ultrahigh group delay of about 6.81 ps is obtained in our proposed design. Our study can provide guidance for various terahertz devices in practical applications.

© 2018 Optical Society of America

Abstract-Displacement Current Mediated Resonances in Terahertz Metamaterials

1. Chao Liu¹, 
2. Kriti Agarwal¹, 
3. Yuping Zhang²,
4. Dibakar Roy Chowdhury³, 
5. Abul K. Azad²and
6. Jeong-Hyun Cho^1,*

Version of Record online: 18 MAY 2016

DOI: 10.1002/adom.201600196

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600196/abstract

Terahertz metamaterials (THz MMs) have been proven to be good candidates for chemical, biological, temperature, strain, and position sensing. However, currently developed thin-metal-film-based split ring resonator (SRR) MMs have relatively low quality factor (Q-factors), leading to a poor sensitivity, which is one of the obstacles for development of sensors. In order to enhance the Q-factor, novel THz MMs, nanopillar-based MMs, are designed, fabricated, and characterized. The nanopillar-based MMs excite the inductive-capacitive resonance via desplacement currents, showing a significantly enhanced Q-factor around 450, which is about 30 times higher than typical thin-metal-film-based MMs. Nanopillar-based MMs also show 17 times larger frequency shift compared to the metal-film-based MMs when the permittivity of the ambient dielectric properties of the MMs changes. Due to high Q-factor and large frequency shift, the nanopillar-based THz MMs utilizing displacement current have great potential for highly sensitive chemical and biomaterial detection as well as frequency-agile THz devices.

Abstract-Graphene based tunable terahertz sensor with double Fano resonances

Yuping Zhang,   Tongtong Li,   Beibei Zeng,   Huiyun Zhang,  Huanhuan Lv,   Xiaoyan Huang,   Weili Zhang and   Abul Azad  

Nanoscale, 2015, Accepted Manuscript

DOI: 10.1039/C5NR03044G
Received 09 May 2015, Accepted 20 Jun 2015
First published online 24 Jun 2015
http://pubs.rsc.org/en/content/articlelanding/2015/nr/c5nr03044g#!divAbstract

We propose an ultrasensitive terahertz (THz) sensor consisting of a subwavelength graphene disk and an annular gold ring within a unit cell. The interference between the resonances arising from the graphene disk and the gold ring gives rise to Fano type resonances and enables ultrasensitive sensing. Our full wave electromagnetic simulations show frequency sensitivity as high as 1.9082THz/refractive index unit (RIU) and a figure of merit (FOM) of 6.5662. Furthermore, the sensing range can be actively tuned by adjusting the Fermi level of graphene.