Abstract-Enabling switchable and multifunctional terahertz metasurfaces with phase-change material

Dacheng Wang, Song Sun, Zheng Feng, and Wei Tan

(a) 3D schematic view of phase-change metasurfaces with switchable and diverse functionalities. Incident terahertz wave is normally irradiated with polarization along x-axis. (b) Top view and (c) side view of the unit cell of the metasurface. The optimized geometrical dimensions are px = py = 135 µm, g1 = 30 µm, g2 = g3 = 10 µm, l = 90 µm, w = 1 µm, d = 15 µm, t1 = 350 nm, t2 = 60 µm, and t3 = 500 nm, respectively.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-10-9-2054

Achieving switchable and diversified functionalities in a single metasurface has garnered great research interest for potential terahertz applications. Here, we propose and demonstrate a phase-change metasurface that simultaneously supports broadband electromagnetically induced transparency (EIT) and broadband nearly perfect absorption, depending on the phase state of a phase change material-vanadium dioxide (VO2). The phase-change metasurface is composed of a VO2 nanofilm, a quartz spacer and gold split-square-ring resonators with VO2 nanopads embedded into the splits. When VO2 is in its insulating phase at room temperature, a broadband EIT window (maximum transmittance reaching 83%) with a bandwidth of 0.27 THz (relative bandwidth 30%) can be observed. Alternatively, when VO2 transforms into its fully metallic phase, the EIT functionality will be switched off and instead, the metasurface operates as a broadband absorber with the total absorption exceeding 93% and a bandwidth of 0.5 THz (relative bandwidth 74%). The electric and magnetic field distributions indicate that the broadband EIT stems from the bright-bright mode coupling and the broadband absorption arises from the excitation and superposition of two resonances within a metal-insulator-metal cavity. The design scheme is scalable from terahertz to infrared and optical frequencies, enabling new avenues towards switchable and multifunctional meta-devices.

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

Abstract-Selective excitation of resonances in gammadion metamaterials for terahertz wave manipulation

DaCheng WANG,  Qin HUANG,  ChengWei QIU,  MingHui HONG,

http://engine.scichina.com/publisher/scp/journal/SCPMA/58/8/10.1007/s11433-015-5674-7?slug=fulltext

A gammadion terahertz (THz) metamaterial embedded with a pair of splits is experimentally investigated. By introducing the pair of splits at different arms, the transmitted amplitude at the resonance frequency can be manipulated from 61% to 24%. Broadband static resonance tunability from 1.11 to 1.51 THz is also demonstrated via varying the relative split positions at certain arms. The amplitude change and static resonance tunability are attributed to the introduced split pairs, which enable selective excitation of different resonance modes in the gammadion metamaterials. This work promises a new approach to design THz functional devices.

Abstract- An ultrathin terahertz quarter-wave plate using planar babinet-inverted metasurface

An ultrathin terahertz quarter-wave plate using planar babinet-inverted metasurface Dacheng Wang, Yinghong Gu, Yandong Gong, Cheng-Wei Qiu, and Minghui Hong  »View Author Affiliations Optics Express, Vol. 23, Issue 9, pp. 11114-11122 (2015) http://dx.doi.org/10.1364/OE.23.011114

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-9-11114

Optics Express, Vol. 23, Issue 9, pp. 11114-11122 (2015)

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Metamaterials promise an exotic approach to artificially manipulate the polarization state of electromagnetic waves and boost the design of polarimetric devices for sensitive detection, imaging and wireless communication. Here, we present the design and experimental demonstration of an ultrathin (0.29λ) terahertz quarter-wave plate based on planar babinet-inverted metasurface. The quarter-wave plate consisting of arrays of asymmetric cross apertures reveals a high transmission of 0.545 with 90 degrees phase delay at 0.870 THz. The calculated ellipticity indicates a high degree of polarization conversion from linear to circular polarization. With respect to different incident polarization angles, left-handed circular polarized light, right-handed circular polarized light and elliptically polarized light can be created by this novel design. An analytical model is applied to describe transmitted amplitude, phase delay and ellipticitiy, which are in good agreement with the measured and simulated results. The planar babinet-inverted metasurface with the analytical model opens up avenues for new functional terahertz devices design.

© 2015 Optical Society of America

Abstract-Coupling effect of spiral-shaped terahertz metamaterials for tunable electromagnetic response

Dacheng Wang, Chengwei Qiu, Minghui Hong
http://link.springer.com/article/10.1007/s00339-013-7928-4
Coupling effect in spiral-shaped metamaterials composed of four half rings at different sizes is investigated to achieve tunability in THz range. This novel spiral-shaped structure was fabricated on flexible substrate with laser micro-lens array (MLA) lithography and measured by THz time domain spectroscopy (THz-TDS). The experimental results suggest that mutual capacitance and inductance coupling in the spiral-shaped structure would result in frequency shifts of the four resonances. The observed shifting trends of the four resonant frequencies are in good agreement with simulation and are further explained by the electric field distribution. By varying the gap sizes among the half rings, four resonant frequencies can be tuned flexibly. Such a spiral-shaped design has potential applications in multi-band tunable THz MEMS devices.