Tunable Nanosensor Based on Fano Resonances Created by Changing the Deviation Angle of the Metal Core in a Plasmonic Cavity

Abstract

In this paper, a type of tunable plasmonic refractive index nanosensor based on Fano resonance is proposed and investigated. The sensor comprises a metal-insulator-metal (MIM) nanocavity with a center-deviated metal core and two side-coupled waveguides. By carefully adjusting the deviation angle and distance of the metal core in the cavity, Fano resonances can be obtained and modulated. The Fano resonances can be considered as results induced by the symmetry-breaking or geometric effect that affects the field distribution intensity at the coupling region between the right waveguide and the cavity. Such a field-distribution pattern change can be regarded as being caused by the interference between the waveguide modes and the cavity modes. The investigations demonstrate that the spectral positions and modulation depths of Fano resonances are highly sensitive to the deviation parameters. Furthermore, the figure of merit (FOM) value is calculated for different deviation angle. The result shows that this kind of tunable sensor has compact structure, high transmission, sharp Fano lineshape, and high sensitivity to the change in background refractive index. This work provides an effective method for flexibly tuning Fano resonance, which has wide applications in designing on-chip plasmonic nanosensors or other relevant devices, such as information modulators, optical filters, and ultra-fast switches.

Magnetic-field sensor with self-reference characteristic based on a magnetic fluid and independent plasmonic dual resonances

“…The sensitivity of an refraction-index sensor is usually defined as the shift in the resonance wavelength per unit variation of refractive index (nm/RIU) [34–35]. The obtained sensitivity for the left peak is 946 nm/RIU, which is comparable to other results [36–39]. For a magnetic sensor, the sensitivity is defined as the wavelength shift per unit variation of magnetic field strength (pm/Oe).…”

Double Fano resonances and electromagnetically induced transparency-like optical response achieved by breaking the symmetry of two double-split rings

“…For example, a structure consisting of a metal-dielectric-metal nanocavity with a center-deviated metal core and two sidecoupled waveguides has been reported, in which both the intensity and wavelength of resonance can be modulated flexibly by changing the structural parameters and the environmental refractive index. This study provides a useful reference for designing plasmonic nanosensors and nonlinear optical devices [2]. Another attractive optical property based on Fano resonance is that the electromagnetic field within the structure is greatly enhanced at the resonance frequency, which also attracts extensive attention of researchers.…”

“…It is an interdisciplinary subject that combines surface plasmon with photonics. Because of its special properties, it has been used in single-molecule biological detection, sub-wavelength aperture transmission and high resolution optical imaging of breaking the diffraction limit, etc The essence of surface plasmons (SPs) is electromagnetic wave in essence, which are generated by the collective oscillation of free electrons on the metal surface under external field excitation [1][2][3]. SPs can be divided into two types: one is propagating surface plasmon polaritons (SPPs), which can propagate along the interface between metal and medium.…”