Abstract
Fano resonances in metamaterial are important due to their low-loss subradiant behavior that allows excitation of high quality (Q) factor resonances extending from the microwave to the optical bands. Fano resonances have recently showed their great potential in the areas of modulation, filtering, and sensing for their extremely narrow linewidths. However, the Fano resonances in a metamaterial system arise from the interaction of all that form the structure, limiting the tunability of the resonances. Besides, sensing trace analytes using Fano resonances are still challenging. In the present work, we demonstrate the excitation of Fano resonances in metamaterial consisting of a period array of two concentric double-split-ring resonators with symmetry breaking (position asymmetry and gaps asymmetry). The tunability and sensing of Fano resonances are both studied in detail. Introducing position asymmetry in the metamaterial leads to one Fano resonance located at 0.50 THz, while introducing gaps asymmetry results in two Fano resonances located at 0.35 THz and 0.50 THz. The transmittance, position, and linewidth of the three Fano resonances can be easily tuned by varying the asymmetry deviations. The Q factor and figure of merit (FoM) of Fano resonances with different asymmetry deviations are calculated for performance optimization. The Fano resonances having the highest FoM are used for the sensing of analytes at different refractive indices, and the Fano resonance performing the best in refractive index sensing is further applied to detect the analyte thickness. The results demonstrate that the tunable Fano resonances show tremendous potential in sensing applications, offering an approach to engineering highly efficient modulators and sensors.
Highlights
Terahertz (THz) waves ranging from 0.1 to 10 THz show huge potential for application in communication [1], imaging [2, 3], biomedicine [4,5,6,7,8], and chemistry [9,10,11,12]
After introducing the position asymmetry (d 2.4 μm), one more transmission dip at 0.50 THz appears for MM-2 besides DD1 and DD2
We have demonstrated that Fano resonances can be excited by introducing asymmetry in the MM formed by a period array of two concentric Split-ring resonator (SRR)
Summary
Terahertz (THz) waves ranging from 0.1 to 10 THz show huge potential for application in communication [1], imaging [2, 3], biomedicine [4,5,6,7,8], and chemistry [9,10,11,12]. It has been found that the dominant radiative losses can be controlled by optimizing the geometry of the metallic subwavelength structure to excite sharp asymmetric resonance with high Q factor. Such resonance is termed as Fano resonance and exhibits a very high Q factor even up to 75 [29]. It is found that Fano resonance shows asymmetric and sharp spectral lines with narrow linewidth and has strongly confined electromagnetic fields Because of these excellent features, Fano resonances have great potential to be applied to the design of THz high Q devices. The transmittance spectra and the electromagnetic field distribution at resonances for different asymmetric deviations were simulated to analyze the coupling between the concentric SRRs within the unit cell. In order to confirm the sensing ability of the tunable Fano resonances, the detection of refractive index, as well as the sensing of analyte thickness, was investigated, and the sensitivities were calculated to evaluate the sensing performance
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