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• Designed a versatile polarization conversion metasurface. • Designed metasurface can switch between transmissive linear-to-linear polarization conversion and reflective quarter-wave plate (QWP). • Designed metasurface with simpler structure and wider bandwidth than similar structures. We propose a dual-pattern broadband polarization converter in the terahertz band using a vanadium dioxide (VO 2) and graphene metasurface. The converter can be switched between transmission and reflection patterns by controlling the phase of VO 2. In the insulating state of VO 2 and with the Fermi energy of graphene (E f) set to 1 eV, the converter works in transmission mode and can convert linearly polarized waves. In the metallic state of VO 2 and with E f set to = 0 eV, the converter works in reflection mode and can function as a quarter-wave plate. The proposed converter is expected to have applications in integrated devices that control the polarization state of terahertz waves. [ABSTRACT FROM AUTHOR]

• We designed a multifunctional all-optically modulated coherent perfect absorber (CPA) metasurface. • The metasurface can switch between dual-band and broadband absorption modes. • Two resonant frequencies of dual-band CPA are temperature-tuned. We propose a temperature-tunable and dual-broadband switchable coherent perfect absorber (CPA) composed of an annulus-disk-shaped InSb pattern and a complementary graphene layer. By controlling the Fermi level of graphene, the temperature of InSb, or the relative phase of incident beams, the working frequency and absorption of the CPA can be continuously adjusted. For a Fermi energy of 0 eV, the dual-band coherent perfect absorptivities exceed 99%. The designed structure achieves broadband absorptance of over 90% in the frequency range of 0.145 THz to 1.24 THz, with a relative bandwidth of about 158.12% for a Fermi energy of 0.5 eV. Moreover, the temperature-dependent permittivity of InSb enables thermal tuning of the dual-band CPA in the THz region. Furthermore, by altering the relative phase of input beams, the absorptivity can be continuously varied between less than 1.2% and more than 90% in the dual-band and broadband modes. Additionally, the designed CPA exhibits insensitivity to the polarization angle within the range of 0° to 90°. Therefore, this multifunctional CPA holds significant potential for applications in modulation, sensing, all-optical switches, and coherent photodetectors. [ABSTRACT FROM AUTHOR]

We theoretically predict and numerically simulate the discrete plasmonic Talbot effect in dielectric graphene plasmonic waveguide (DGPW) arrays at THz wavelengths. The super-modes in DGPW arrays are analyzed by using super-mode theory and the field intensity distributions in the designed DGPW arrays are explained by the superposition of different super-modes and simulated by using commercial software (COMSOL) based on finite element method (FEM). The discrete plasmonic Talbot effect is realized by superposition of different super-modes. The Talbot distance can be actively tuned by varying the Fermi energy of graphene and it decreases monotonically with increasing Fermi energy. In addition, it is found that the Talbot distance increases with the period of the DGPW arrays. Simulation results show a good agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Graphene can be utilized in designing tunable photonic devices due to its unique properties such as high optical transparency and tunable conductivity. In this paper, a tunable triple-band perfect absorber is designed and numerically demonstrated, which is composed of a stacked graphene nanodisk, L-shape graphene layer and a gold ground plane spaced by insulator layers. The results show that there are three higher than 99% absorption peaks in the infrared range with a wide incident angle range up to 50°, and the absorber is insensitive for TE and TM polarized incident light. Moreover, the perfect absorption peak wavelength can be tuned by changing Fermi levels or geometric parameters of graphene layers. The findings above indicate that the designed perfect absorber can be used in the field of photodetectors, thermal emitters and photovoltaics. Image 105556 As shown in the Figure (a) the tunable triple-band perfect absorber which is composed of a stacked graphene nanodisk, L-shape graphene layer and a gold ground plane spaced by insulator layers and the absorption can be significantly enhanced due to the SPPs in graphene layers. Absorption spectra for the structure shown in Figure. (b) (black solid line), the structure without an array of L-shaped graphene (yellow dashed line), and the structure without an array of graphene nanodisks (red dashed line). Figure (c) shows absorption spectra for TE wave with different incident angles θ. [ABSTRACT FROM AUTHOR]

A multifunctional metasurface based on graphene and vanadium dioxide (VO 2), which can function as a broadband absorber, half-wave plate (HWP), and quarter-wave plate (QWP) in the terahertz frequency band, is designed in this study. When VO 2 is in the metal phase, the multifunctional metasurface operated as a broadband absorber in the range of 0.89–2.36 THz. The designed multifunctional metasurface can switch between HWP and QWP by adjusting the Fermi energy of graphene through voltage biasing when VO 2 is in the insulated phase. When the Fermi level of graphene is 0 eV, the designed structure acts as an HWP to achieve linear-to-linear (LTL) polarization conversion and preserve the reflection chirality of circular polarization at 0.68–2.64 THz. When E f = 0.3 eV, the designed structure functions as a QWP in 0.89–2.51 THz to realize the interconversion of linear polarization and circular polarization. Furthermore, the effects of the polarization and incidence angles on the operating performance are discussed. This study demonstrates that the multifunctional metasurface has promising applications in terahertz optical switches, electromagnetic stealth, modulators, and communication systems. [Display omitted] • A multifunctional metasurface has been designed. • The designed metasurface can switch between broadband absorber and polarization converter. • The designed metasurface can switch between half-wave plate (HWP) and quarter-wave plate (QWP). [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A surface plasmon resonance-based biosensor is proposed. • Graphene is utilized to increase the adsorbability in biosensors. • Barium titanate layer is used to improve the performance of SPR biosensor. • Our proposed SPR biosensor has better performance than those reported. Abstract A surface plasmon resonance-based biosensor, consisting prism, silver, barium titanate (BaTiO 3) and graphene layers, is presented by using angular interrogation. The structure is specially designed to further enhance the sensitivity and to decrease the full width at half maximum (FWHM) thereby improving the sensor performance. Theoretical analysis shows that the highest sensitivity can reach at 257°/RIU where the thickness of Ag layer is 45 nm with 10 nm BaTiO 3 and one graphene layer. Compared with existing biosensors, the proposed biosensor exhibits higher sensitivity, lower FWHM and two times better preformation in the quality factor of the sensor, which would make our design have more applications in the field of biosensors. [ABSTRACT FROM AUTHOR]

Abstract Graphene as a promising material for terahertz-infrared region plays an important role in nanoplasmonic devices owing to its tunability. We propose a hybrid graphene nanoplasmonic waveguide and analyze its propagation properties by finite element method. The results show that the light in terahertz-infrared region can be confined at low-index material and the fundamental mode can be tuned flexibly by changing Fermi energy level of graphene. Then an application of the designed waveguide, an electrically controllable directional coupler is designed and its performance is numerically verified. This approach can be extended to novel designs of nanoscale integrated photonic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A versatile terahertz graphene metasurface has been designed. • Tunable PIT effect in two perpendicular polarization directions was realized. • The penta-frequency and dual-frequency switch can be implemented. • High sensitivity (30500 nm/RIU) can be obtained with the designed metasurface. • Outstanding slow-light effect can be obtained with the designed metasurface. A monolayer terahertz graphene metasurface is designed to achieve tunable plasmon-induced transparency (PIT) effect in two perpendicular polarization directions based on surface plasmon polariton resonance. The penta-frequency and dual-frequency switch can be easily implemented by adjusting the Fermi levels of graphene, and the switch has excellent performances including modulation degree of amplitude (81.4 % < MDA < 97.1 %) and insertion loss (0.01 dB < IL < 0.04 dB). Moreover, the metasurface has high sensitivity, which can be up to 30500 nm/RIU. Also, the designed PIT metasurface has a good slow light effect, and group indexes are respectively 1100 and 2396 corresponding to x-polarized and y-polarized light. This work demonstrates that graphene metasurface has potential applications in switch, sensor and slow-light devices. [ABSTRACT FROM AUTHOR]