Abstract-Bifunctional terahertz modulator for beam steering and broadband absorption based on a hybrid structure of graphene and vanadium dioxide

 

Wenwen Liu, Jiashuai Xu, Zhengyong Song

Schematic diagram of the proposed structure. (a) The whole 3D structure. (b) Schematic of 3D unit cell. (c) Top view of graphene patch.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-15-23331&id=453128

A bifunctional metamaterial is proposed based on a hybrid graphene and vanadium dioxide (VO2) configuration, which can realize a dynamic switch between beam steering and broadband absorption. The structure consists of a VO2 square, graphene patch, topas spacer, VO2 film, topas spacer, and metal substrate. When VO2 is in the metallic state, the structure serves as a coding metamaterial. By engineering different sizes of the top VO2 square and adjusting the Fermi energy level of graphene, the incident wave is scattered in different patterns. When VO2 is in the dielectric state, the structure serves as a broadband absorber. By changing the Fermi energy level of graphene from 0.0 eV to 0.9 eV, absorptance can be gradually changed and working bandwidth widens. There is an absorption band with near 100% absorptance from 0.9 THz to 1.35 THz when the Fermi energy level is 0.73 eV. And the designed broadband absorber is polarization-insensitive within the incident angle of 50°. Our work may show great potential in applications such as terahertz switching and modulation.

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

Abstract-Achieving broadband absorption and polarization conversion with a vanadium dioxide metasurface in the same terahertz frequencies

Zhengyong Song and Jiahe Zhang

Schematic of the designed switchable metasurface, consisting of periodic square-shaped VO2, SiO2 spacer, gold strip, VO2 film, and SiO2 spacer, and the bottom gold film.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-8-12487

We present the bifunctional design of a broadband absorber and a broadband polarization converter based on a switchable metasurface through the insulator-to-metal phase transition of vanadium dioxide. When vanadium dioxide is metal, the designed switchable metasurface behaves as a broadband absorber. This absorber is composed of a vanadium dioxide square, silica spacer, and vanadium dioxide film. Calculated results show that in the frequency range of 0.52-1.2 THz, the designed system can absorb more than 90% of the energy, and the bandwidth ratio is 79%. It is insensitive to polarization due to the symmetry, and can still work well even at large incident angles. When vanadium dioxide is an insulator, a terahertz polarizer is realized by a simple anisotropic metasurface. Numerical calculation shows that efficient conversion between two orthogonal linear polarizations can be achieved. Reflectance of a cross-polarized wave can reach 90% from 0.42 THz to 1.04 THz, and the corresponding bandwidth ratio is 85%. This cross-polarized converter has the advantages of wide angle, broad bandwidth, and high efficiency. So our design can realize bifunctionality of broadband absorption and polarization conversion between 0.52 THz and 1.04 THz. This architecture could provide one new way to develop switchable photonic devices and functional components in phase change materials.

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

Abstract-Terahertz bifunctional absorber based on a graphene-spacer-vanadium dioxide-spacer-metal configuration

Man Zhang and Zhengyong Song

3D diagram of the proposed bifunctional metamaterial absorber.

Simulated electric field distributions in the XOY plane at the peak frequencies of 1.25 THz (a) and 2.13 THz (b) for broadband absorption, and simulated magnetic field distribution in the XOZ plane at 1.37 THz (c) for narrowband absorption.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-8-11780

A terahertz bifunctional absorber is presented with broadband and narrowband absorbing properties in a graphene-spacer-vanadium dioxide-spacer-metal configuration. Carrier relaxation time of graphene τ = 1.0ps (τ = 0.1ps) is chosen for narrowband (broadband) absorption. When vanadium dioxide is in the conducting state, the design behaves as a narrowband absorber, and it is composed of a square-shaped graphene, topas spacer, and metallic vanadium dioxide film. There is an absorption band with 100% absorptance at the frequency of 1.37 THz. Narrowband absorption is caused by the localized magnetic resonance. When vanadium dioxide is in the insulating state, the design behaves as a broadband absorber composed of a square-shaped graphene, topas layer, vanadium dioxide film, and metal film. It has a broadband absorption in the frequency range of 1.05-2.35 THz, and the corresponding absorptance is more than 90%. The merging of two resonances with overlapping region ensures broadband performance of the designed absorber. The working bandwidth and intensity of narrowband absorption and broadband absorption can be dynamically adjusted by changing the Fermi energy level of graphene. The influences of structure parameters are discussed on absorption performance. In addition, the designed absorber is not sensitive to incident angle. Because of the simple structure, our design can be applied to many promising fields in intelligent absorption and terahertz switch.

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

Abstract-Ultra-broadband wide-angle terahertz absorber realized by a doped silicon metamaterial

Author links open overlay panelMingwei Jiang, Zhengyong Song, Qing Huo,


https://www.sciencedirect.com/science/article/abs/pii/S0030401820303308

Metamaterial absorber as a functional device has been extensively studied in the past decade, and its performance is continuously improved. Here we present a wide-angle terahertz absorber through polarization-insensitive doped silicon. The structural unit cell consists of a square silicon ring and a silicon substrate. Full-wave simulated results show that the designed absorber has excellent performance in the frequency range of 0.7-5.7 THz with the center frequency of 3.2 THz. The relative bandwidth ratio is 156.25% with absorptance greater than 90%. The design is insensitive to polarization at the small incident angle and still shows good performance over a wide range of incident angle. The proposed system may find potential applications in terahertz energy harvesting and thermal emission.

Abstract-Terahertz switching between broadband absorption and narrowband absorption

Zhengyong Song, Apeng Chen, and Jiahe Zhang, 

The calculated absorptances with different conductivities of VO2.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-2-2037

A multilayer metamaterial with switchable functionalities is presented based on the phase-transition property of vanadium dioxide. When vanadium dioxide is in the metallic state, a broadband absorber is formed. Calculated results show that the combination of two absorption peaks enables absorptance more than 90% in the wide spectral range from 0.393 THz to 0.897 THz. Absorption performance is insensitive to polarization at the small incident angle and work well even at the larger incident angle. When vanadium dioxide is in the insulating state, the designed system behaves as a narrowband absorber at the frequency of 0.677 THz. This narrowband absorber shows the advantages of wide angle and polarization insensitivity due to the localized magnetic resonance. Furthermore, the influences of geometrical parameters on the performance of absorptance are discussed. The proposed switchable absorber can be used in various applications, such as selective heat emitter and solar photovoltaic field.

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

Abstract-Broadband tunable absorber for terahertz waves based on isotropic silicon metasurfaces

Zhengyong Song,  Zhisheng Wang, Maoliang Wei,

https://www.sciencedirect.com/science/article/pii/S0167577X18314629

A broadband tunable absorber is studied based on the silicon metasurface at terahertz frequencies. By tuning the conductivity of silicon, absorptance is more than 90% from 0.497 THz to 1.045 THz with central frequency of 0.771 THz when the conductivity is equal to $\mathit{PleaseCheck}$. Simulated results show that absorptance peak can be modulated from 1% to 100% when the conductivity continuously changes from $\mathit{PleaseCheck}$ to $\mathit{PleaseCheck}$. The central-symmetry structure leads to polarization independence. Our design may be used as optoelectronic modulator, tunable detector, and terahertz switch.

Abstract-Omnidirectional tunable terahertz analog of electromagnetically induced transparency realized by isotropic vanadium dioxide metasurfaces

Qiongqiong Chu, Zhengyong Song, Qing Huo Liu,

http://iopscience.iop.org/article/10.7567/APEX.11.082203

We present an isotropic active analog of electromagnetically induced transparency through conductivity tuning of vanadium dioxide at terahertz frequencies. The unit cell of the designed metasurface consists of metallic split ring resonators and a metallic cross, which have identical resonance frequencies for the excitable lowest order modes but very different linewidths. By integrating vanadium dioxide into the bottom of the metasurface, an obvious tuning of the transparency window occurs under different conductivities. Calculated results show that resonant transmission frequency of the electromagnetically induced transparency remains stable with respect to the polarization and incident angle of electromagnetic waves.

Abstract-Isotropic wide-angle analog of electromagnetically induced transparency in a terahertz metasurface

Zhengyong Song, Qiongqiong Chu, Qing Huo Liu

https://www.sciencedirect.com/science/article/pii/S0167577X18306025

We present a terahertz classical analog of electromagnetically induced transparency by means of single-layer metamaterial consisting of two closed square ring. The narrow transparency peak is mainly caused by the excitation of antiparallel currents in different rings. Because of symmetry configuration, the designed metamaterial possesses stable polarization-independent and wide-angle transmission spectral features. Moreover, the design has a simple structure ideally suitable for the current planar micro- and nano-fabrications.

Abstract-Broadband tunable terahertz absorber based on vanadium dioxide metamaterials

Zhengyong Song, Kai Wang, Jiawen Li, and Qing Huo Liu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-6-7148

An active absorption device is proposed based on vanadium dioxide metamaterials. By controlling the conductivity of vanadium dioxide, resonant absorbers are designed to work at wide range of terahertz frequencies. Numerical results show that a broadband terahertz absorber with nearly 100% absorptance can be achieved, and its normalized bandwidth of 90% absorptance is 60% under normal incidence for both transverse-electric and transverse-magnetic polarizations when the conductivity of vanadium dioxide is equal to 2000 𝛺−1𝑐𝑚−1$2000{\Omega }^{-1}c{m}^{-1}$. Absorptance at peak frequencies can be continuously tuned from 30% to 100% by changing the conductivity from 10 𝛺−1𝑐𝑚−1$10{\Omega }^{-1}c{m}^{-1}$ to 2000 𝛺−1𝑐𝑚−1$2000{\Omega }^{-1}c{m}^{-1}$. Absorptance spectra analysis shows a clear independence of polarization and incident angle. The presented results may have tunable spectral applications in sensor, detector, and thermophotovoltaic device working at terahertz frequency bands.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Broadband absorber with periodically sinusoidally-patterned graphene layer in terahertz range

Longfang Ye, Yao Chen, Guoxiong Cai, Na Liu, Jinfeng Zhu, Zhengyong Song, and Qing Huo Liu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-10-11223

We demonstrate that a broadband terahertz absorber with near-unity absorption can be realized using a net-shaped periodically sinusoidally-patterned graphene sheet, placed on a dielectric spacer supported on a metallic reflecting plate. Because of the gradient width modulation of the unit graphene sheet, continuous plasmon resonances can be excited, and therefore broadband terahertz absorption can be achieved. The results show that the absorber’s normalized bandwidth of 90% terahertz absorbance is over 65% under normal incidence for both TE and TM polarizations when the graphene chemical potential is set as 0.7 eV. And the broadband absorption is insensitive to the incident angles and the polarizations. The peak absorbance remains more than 70% over a wide range of the incident angles up to 60° for both polarizations. Furthermore, this absorber also has the advantage of flexible tunability via electrostatic doping of graphene sheet, which peak absorbance can be continuously tuned from 14% to 100% by controlling the chemical potential from 0 eV to 0.8 eV. The design scheme is scalable to develop various graphene-based tunable broadband absorbers at other terahertz, infrared, and visible frequencies, which may have promising applications in sensing, detecting, and optoelectronic devices.

© 2017 Optical Society of America