Ben-Xin Wang

Combined theoretical analysis for plasmon-induced transparency in integrated graphene waveguides with direct and indirect couplings

By taking a graphene nanoribbon as a resonator, we have numerically and analytically investigated the spectral characteristics of plasmon-induced transparency in integrated graphene waveguides. For the indirect coupling, the formation and evolution of the transparency window are determined by the excitation of the super resonances, as well as by the destructive interference and the coupling strength between the two resonators, respectively, while for the indirect coupling, the peak transmission and corresponding quality factor can be dynamically tuned by adjusting the Fermi energy of graphene nanoribbons and the transparency peak shifts periodicity with the round-trip phase accumulated in the graphene waveguide region. Analytical results based on temporal coupled mode theory (CMT) show good consistence with the numerical calculations. Our findings may support the design of ultra-compact plasmonic devices for optical modulating.

Actively Tunable Fano Resonance Based on a T-Shaped Graphene Nanodimer

We present the strength modulation and frequency tuning of Fano resonance by employing a graphene nanodimer formed by two coplanar perpendicular nanostrips with different dimensions. The Fano resonance is induced by destructive interference between the bright dipole mode of a short nanostrip and the dark quadrupole mode of a long nanostrip. The strength, line width, and resonance frequency of the Fano resonance can be actively modulated by changing the spatial separation of those two graphene nanostrips and the Fermi energy of the graphene nanodimer, respectively, without re-fabricating the nanostructures. The tuning of the strength and resonance frequency can be attributed to the coupling strength and optical properties of graphene, respectively. Importantly, a figure of merit value as high as 39 is achieved in the proposed nanostructures. Our results may provide potential applications in optical switching and bio-chemical sensing.

Design of a Five-Band Terahertz Absorber Based on Three Nested Split-Ring Resonators

A novel five-band terahertz metamaterial absorber based on three nested split-ring resonators is proposed. It is found that the structure has five distinctive absorption bands whose peaks are average over 99%. Different from previous reports by combing the resonances of the complex structure to obtain the multi-band responses, the proposed five-band absorber uses the hybrid of the LC resonance and dipolar response of the patterned structure, thus making the proposed structure quite easy to be fabricated. Furthermore, the sensing performance of the absorber is analyzed in terms of the over layer and the surrounding index.

Ultra-narrow terahertz perfect light absorber based on surface lattice resonance of a sandwich resonator for sensing applications

Perfect light absorbers have attracted much attention because of their potential applications in solar cells, thermal imaging, material detection, bio-sensing, and others. However, it is extremely difficult to obtain the ultra-narrow bandwidth of a perfect light absorber in the terahertz region. Herein, an ultra-narrow terahertz perfect light absorber based on the surface lattice resonance of three stacking layers, namely a square resonator, a dielectric spacer, and a metallic film, is reported. A resonance absorption peak with bandwidth of 0.0200 THz and absorption rate of 98.86% is realized. The absorption performance of the device can be controlled by employing different sized (unit) periods and dielectric spacer thicknesses. Particularly, the device bandwidth can be decreased by reducing the dielectric layer thickness. At a certain thickness, a resonance peak with a bandwidth of only 0.0067 THz is achieved. This peak is very sensitive to the surrounding refractive index. The large sensitivity (2.58 THz per refractive index) and simultaneous ultra-narrow bandwidth lead to an ultra-high figure of merit (385.07), making this a promising light device in terahertz detection and sensing.

Quad-Band Terahertz Absorber Based on Dipolar Resonances of Metamaterial Resonator

A novel design of a quad-band metamaterial absorber, which consisted of only a metallic resonator on top of a dielectric spacing layer and a metallic board on the bottom, is presented in this paper. Four near-perfect resonance peaks are observed in this structure. The combination of four dipolar resonances in different sections of the resonator results in the quad-band absorption. The absorption performance, including the operating frequencies and number of the resonance peaks, of the metamaterial can be controlled by changing the parameters of the resonator. The quad-band absorption is very promising for highly integrated absorbing devices.

New Type Design of the Triple-Band and Five-Band Metamaterial Absorbers at Terahertz Frequency

A new scheme to achieve a simple design of triple-band metamaterial absorber at terahertz frequency is presented. In this scheme, we employ a traditional sandwich structure, which is consisted of a metallic resonator and an appropriate thickness of the dielectric layer backed with an opaque metallic board, as the research object. Three strong but discrete resonance peaks with the narrow bandwidths and high absorptivities are realized. The combination of the dipolar resonance, LC (inductor-capacitor circuit) resonance, and the surface resonance of the metallic resonator determines the triple-band absorption. Numerical results also show that the frequencies of the three absorption bands and the number of the resonance peaks can be effectively tuned by adjusting or changing the geometric parameters of the metallic resonator. Moreover, we present a simple design of five-band terahertz absorber by further optimizing the sizes of the metallic elements in the top layer of the metamaterial. The design of the unit structures will assist in designing innovative absorbing devices for spectroscopy imaging, detection, and sensing.

Single Metamaterial Resonator Having Five-Band Terahertz Near-Perfect Absorption

New strategy to achieve a simple design of a five-band terahertz absorber is demonstrated. We take a sandwiched metamaterial structure as the study object, which is consisted of an array of Au resonator and a dielectric spacing layer on top of an opaque Au board. Five distinct but large absorption rates of peaks are realized. The combination of the five modes in different sections of the device determines the multiple-band absorption. Field distributions of these modes are given to insight into their physical mechanism. The five-band absorber gives important potentials to develop integrated terahertz devices.

Design of Dual-Band Plasmon-Induced Transparent Effect Based on Composite Structure of Closed-Ring and Square Patch

We propose a dual-band transparent window terahertz metamaterial consisting of a closed-ring resonator and a square patch. This structure can achieve two transparent windows with transmission intensity of more than 90%. The formation of the two windows can be attributed to the coupling of the localized resonance modes between the closed-ring and square patch. The influence of the geometrical dimensions of the closed-ring resonator and the square patch on the transmitted spectrum is also discussed; it is found that the change of sizes can strongly affect the frequencies of the two transparent windows. This novel terahertz metamaterial may open up new avenues toward the control of terahertz waves in many technology-related areas.