Tunable Dual-band Perfect Absorber Research Articles

Graphene-based dual-band tunable perfect absorber in THz range

ABSTRACT We design and simulate a tunable dual-band perfect absorber. This absorber is composed of a circular graphene layer with an ellipse cut out in the centre, separated by a dielectric layer in the middle and a gold mirror at the bottom. Results reveal that there exist two perfect absorption peaks in the terahertz band. The position of the absorption peak can be changed by adjusting the Fermi level and geometric parameters of the graphene pattern. Furthermore, the absorber is insensitive to the polarized incident light with a wide incident angle. Functionalities are achieved based on a simple and symmetrical single-layer graphene pattern, which can greatly reduce the manufacturing costs. The proposed absorber can be applied in the field of graphene-based photonic devices, such as detectors, sensors, and filters.

Ultra high-sensitivity and tunable dual-band perfect absorber as a plasmonic sensor

In this paper, we demonstrate a dual-band tunable absorber coupled with a nanoscale metal-dielectric-metal (MDM) structure for sensing applications in the near-infrared spectral region. This structure exhibits a dipole resonance mode in absorbance and reflectance spectra which results in the enhancement of absorbance over a wide range of incident angles for TE polarization. Using a numerical and analytical study, the performance parameters of the structure including sensitivity (SS), the figure of merit (FoM) and quality factor (Q) are investigated by changing the incident polarization, geometrical parameters, filling dielectric and plasmonic metasurface material. Moreover, we study the dependence of the sensitivity as a function of plasmonic metasurface shape to demonstrate a better response compared with other methods. Results show that, in terms of the refractive index unit (RIU), an ultra-high sensitivity and tunable sensor can be designed with a maximum sensitivity of 1240.8 nm/RIU for a refractive index change of Δn = 0.0458. In the optimum design of the proposed dual-band absorber, a Q-factor and FoM equal to 123.45 and 44.5 are obtained. Furthermore, the proposed structure can be utilized for controlling the light propagation. By considering silver as a plasmonic metasurface, a slow down factor as high as 680 is obtained. Our work will be applied to future sensors capable of ultra-high sensitivity.

Tunable dual-band plasmonic perfect absorber and its sensing applications

We theoretically present a tunable dual-band perfect absorber in the visible and near-infrared regions for sensing applications. The absorber consists of a periodic metal-dielectric-metal shell-core nanorod array and a thick metal film separated by a periodic dielectric nanorod array. Two narrow perfect absorption bands (98.2% and 99.7%) are achieved due to the synergy of localized surface plasmons (LSPs), propagating surface plasmons (PSPs) and lattice resonances. The two narrow bands both are sensitive to the refractive index change and the maximum sensitivity is 783.705 nm/RIU (RIU is the refractive index unit). These enable the structure to have great potential in the fields of perfect absorbers, plasmonic sensors, and filters.

Tunable dual-band perfect absorber consisting of periodic cross-cross monolayer graphene arrays

Abstract In this paper, we propose a tunable dual-band perfect absorber, which makes the thicker SiO2 dielectric as a spacer to separate the gold layer from the periodic cross-cross monolayer graphene array layer which locates the roof of whole absorber. The simulation results indicate that transforming the periodic p, the geometrical parameters of array and the thickness of SiO2 medium can make the structure achieve perfect absorption in dual-band. Moreover, the resonance wavelength and absorption peak can be flexibly selected by Fermi level and relaxation time. In addition, the absorber is insensitive to incident angle, whether TM polarization or TE polarization. Therefore, the study provides a novel inspiration for the design of graphene-based tunable multi-band perfect THz absorber, which can be applied to photodetectors, chemical sensors and other optoelectronic devices.

Tunable Dual-Band Perfect Absorber Based on L-Shaped Graphene Resonator

We propose and investigate a tunable dual-band perfect absorber consisting of double asymmetric L-shaped graphene resonators (LSGRs) and a metal ground plane spaced by a thin SiO2 dielectric layer. The numerical results reveal that the presented absorber expresses two resonance peaks in the mid-infrared region, where their absorption coefficients are on average larger than 98.77%. The electromagnetic eigenmode resonances of a single LSGR can induce two absorption peaks with values about 50%. Assembling two LSGRs together, the absorptivity can reach up to almost 100% due to the plasmonic couplings. In addition, the design has the ability to tune the working wavelengths of the absorption peaks within a large wavelength range by changing geometric parameters and the Fermi level of the graphene layer. In addition, wavelength-selective dual-band perfect absorption peaks can be achieved in the wavelength range of interest by merely adjusting the polarization angle. This letter presents a unique route toward the realization of nanophotonic devices and has potential applications in filtering, sensing, and detecting.

Independently tunable dual-band perfect absorber based on graphene at mid-infrared frequencies.

We design a dual-band absorber formed by combining two cross-shaped metallic resonators of different sizes within a super-unit-cell arranged in mirror symmetry. Simulations indicate that absorption efficiencies greater than 99% can be achieved at two different frequencies under normal incidence. We employ a design scheme with graphene integration, which allows independent tuning of individual absorption frequencies by electrostatically changing the Fermi energy of the graphene layer. High absorbance is maintained over a wide incident angle range up to 50 degrees for both TE and TM polarizations. It thus enables a promising way to design electrically tunable absorbers, which may contribute toward the realization of frequency selective detectors for sensing applications.

Tunable dual-band perfect absorbers based on extraordinary optical transmission and Fabry-Perot cavity resonance

Magnetic resonance is considered to be a necessary condition for metamaterial perfect absorbers, and dual-band absorbers can be composed of a pair of metallic layers with anti-parallel surface currents. We designed and fabricated a tunable dual-band perfect absorber based on extraordinary-optical-transmission (EOT) effect and Fabry-Perot cavity resonance. The idea and the mechanism are completely different from the absorber based on the near-field interaction. The important advantage of our structure is that we can switch a single-band absorber to a dual-band absorber by changing the distance between two metallic layers and/or incident angle. The peak originating from the EOT effect becomes significantly narrower, resulting in an increase of the Q-factor from 16.88 to 49. The dual-band absorber can be optimized to be insensitive to the polarization of the incident electromagnetic wave by slightly modifying the absorber structure.