Dual-Band Plasmonic Perfect Absorber Based on Graphene Metamaterials for Refractive Index Sensing Application

Abstract

We demonstrate a dual-band plasmonic perfect absorber (PA) based on graphene metamaterials. Two absorption peaks (22.5 μm and 74.5 μm) with the maximal absorption of 99.4% and 99.9% have been achieved, respectively. We utilize this perfect absorber as a plasmonic sensor for refractive index (RI) sensing. It has the figure of merit (FOM) of 10.8 and 3.2, and sensitivities of about 5.6 and 17.2 μm/RIU, respectively. Hence, the designed dual-band PA-based RI sensor exhibits good sensing performance in the infrared regime, which offers great potential applications in various biomedical, tunable spectral detecting, environmental monitoring and medical diagnostics.

Keywords: graphene; metamaterials; refractive index sensor; surface plasmon resonance.

Figure 1

(a) Schematic of the perfect absorber structure; (b) the incident light polarization configuration (TM-polarization, TM-polarization indicates that the direction of the incident electric field is along the x axis); and (c) the schematic geometry of a top gate configuration to manipulate the Fermi energy of graphene. Parameters: d₁ = 3 μm, d_g = 0.45 μm, d₂ = 4.17 μm, t = 1 nm, R_in = 0.8 μm, R_out = 1.05 μm, D = 0.2 μm, L = 0.7 μm, G = 0.25 μm, and W = 0.25 μm. The periods in both x and y-directions are 2.5 μm. The whole structure resides on a substrate (n₁ = 3.4).

Figure 2

(a) Absorption (A), reflective (R), and transmission (T) spectrum of the presented structure; (b,c) are the electric field distribution of the corresponding graphene and the simulated surface charge density distributions at λ₁ = 22.5 μm and λ₂ = 74.5 μm, respectively.

Figure 3

The effect of different parameters of the absorber on the absorption spectrum: (a) the outer ring radius of the graphene (R_out); (b) L, (c) D, (d) G. The Fermi level of graphene is 1.0 eV in (b), (c), and (d). The insert graph is the absorption peak of Mode A or Mode B.

Figure 4

The absorption spectra of the proposed structure with different period P. The insert graph is the absorption peak of Mode A.

Figure 5

For TM polarization, (a) absorption spectrum of the absorber with different Fermi levels (the insert graph is absorption of Mode A) and (b) relaxation times. The insert graph is the absorption peak of Mode B.

Figure 6

(a) Spectral shift of mode A and mode B with different sensing medium refractive indices (1.0–1.5) (the insert map is spectral shift of mode A); (b) a linear relationship of resonance wavelengths in response to changes in the refractive index; (c) FWHM (FWHM is the full width of half maximum) and figure of merit (FOM) of mode A and mode B in response to different sensing medium refractive indices.