Fano resonance with high local field enhancement under azimuthally polarized excitation

Abstract

Being an enabling technology for applications such as ultrasensitive biosensing and surface enhanced spectroscopy, enormous research interests have been focused on further boosting the local field enhancement at Fano resonance. Here, we demonstrate a plasmonic Fano resonance resulting from the interference between a narrow magnetic dipole mode and a broad electric dipole mode in a split-ring resonator (SRR) coupled to a nanoarc structure. Strikingly, when subjected to an azimuthally polarized beam (APB) excitation, the intensity enhancement becomes more than 60 times larger than that for a linearly polarized beam (LPB). We attribute this intensity enhancement to the improved conversion efficiency between the excitation and magnetic dipole mode along with improved near-field coupling. The APB excited Fano structure is further used as a nanoruler and beam misalignment sensor, due to the high sensitivity of intensity enhancement and scattering spectra to structure irregularities and excitation beam misalignment. Interestingly, we find that, regardless of the presence of structural translations, the proposed structure still maintains over 60 times better intensity enhancement under APB excitation compared to LPB excitation. Moreover, even if the APB excitation is somewhat misaligned, our Fano structure still manages to give a larger intensity enhancement than its counterpart excited by LPB.

Near-infrared dual-wavelength plasmonic switching and digital metasurface unveiled by plasmonic Fano resonance

“…Next, when the geometric parameters of the unit cells are fixed, the modulated polarization direction of the incident light could potentially induce the change of the coupling strength of the electric field with the hybrid metasurface [11]. As shown in Figure 3d-f, the polar plots of the transmittance at the related three wavelengths (corresponding to the blue square, black dot, and red triangle in Figure 3a-c, respectively) in the hybrid metasurface with b p = 40, W = 150 nm, and D = 10 nm are considered.…”

“…As a universal phenomenon in optics, FR with an asymmetric profile in optical response can be observed in the plasmonic nanostructures [3,4], electromagnetic metamaterials [3,5], photonic crystals [6,7], semiconductor nanostructures [8][9][10], etc. Plasmonic FR that originates from the destructive interference between the superradiant and subradiant resonance modes with a spectrum overlapping in the metallic subwavelength nanostructures has characteristics similar to the traditional FR in the interacting quantum systems [11,12]. In particular, by coherently interacting with the superradiant mode, the subradiant mode that is only weakly coupled with the free space results in the presence of plasmonic FR along with a narrow spectral feature, which can be termed as wavelength selectivity [13].…”

Enhanced second harmonic generation from a plasmonic Fano structure subjected to an azimuthally polarized light beam

“…Figure 3(a) shows the LPB excited scattering spectrum of the SRR/nanoarc structure (red solid curve), where a Fano lineshape can be found [50]. The Fano resonance of our designed structure stems from the interference between the subradiant magnetic dipole mode supported by individual SRR (blue dashed curve in figure 3(a)) and the superradiant electric dipole mode supported by individual nanoarc (orange dashed curve in figure 3(a)).…”

Magnetic Fano resonance of heterodimer nanostructure by azimuthally polarized excitation

“…These two interacting modes could be regarded as two coupled oscillators, the two oscillators provide the bonding mode and anti-bonding mode. The equation governing the motions of the two oscillators can be written as [40][41][42]…”