Tunable angle-independent refractive index sensor based on Fano resonance in integrated metal and graphene nanoribbons.

Meiyan Pan,Yu Wang,Zhaoxing Liang,Yihang Chen

doi:10.1038/srep29984

Meiyan Pan, Yu Wang + Show 2 more

Open Access

https://doi.org/10.1038/srep29984

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Abstract

We propose a novel mechanism to construct a tunable and ultracompact refractive index sensor by using the Fano resonance in metal-graphene hybrid nanostructure. Plasmon modes in graphene nanoribbons and waveguide resonance modes in the slits of metal strip array coexist in this system. Strong interference between the two different modes occurs when they are spectrally overlapped, resulting in a Fano-type asymmetrically spectral lineshape which can be used for detecting the variations of ambient refractive index. The proposed sensor has a relatively high figure of merit (FOM) over 20 and its sensing performance shows a good tolerance to roughness. In addition to the wide range measurement enabled by the electrical tuning of graphene plasmon modes, such ultracompact system also provides an angle-independent operation and therefore, it can efficiently work for the detection of gas, liquid, or solids. Such optical nanostructure may also be applied to diverse fields such as temperature/pressure metering, medical detection, and mechanical precision measurement.

Highlights

Exhibiting an asymmetric profile of spectral lineshape, Fano resonance (FR) was first experimentally observed by Beutler[1] and theoretically interpreted by Ugo Fano[2]
Plasmonic devices based on the coupled SP modes require a spatial period with the same order of magnitude of the resonant wavelength, resulting in inevitably large dimensions at infrared and terahertz regime, and their performance strongly depends on the incident angle
Finite-difference time-domain (FDTD) method was used to calculate the transmission spectra, where parameters of silver are obtained from experimental data (Palik)[17]

Summary

Introduction

Exhibiting an asymmetric profile of spectral lineshape, Fano resonance (FR) was first experimentally observed by Beutler[1] and theoretically interpreted by Ugo Fano[2]. A manner to obtain FR is to break the geometric symmetry of nanostructures[4], by which sharp subradiant modes (high-order oscillations) were excited and interacted with the broad superradiant mode (dipole) Another compelling approach is by using grating structures[5] where localized particle plasmons and optical waveguide modes coexist. Graphene and silver nanoribbons are deposited, with a sub-wavelength period, on a PMMA/Ag/PMMA substrate to generate spectrally overlapped GSP and waveguide-mode resonance. The interaction of these two SPs can lead to a Fano-type asymmetric lineshape used for sensing the changes in refractive index. Our proposed mechanism for the design of refractive index sensors can be applied in far infrared and terahertz regimes

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Conclusion