Abstract
A kind of plasmonic structure consisted of an equilateral triangle-shaped cavity (ETSC) and a metal-insulator-metal (MIM) waveguide is proposed to realize triple Fano resonances. Numerically simulated by the finite difference time domain (FDTD) method, Fano resonances inside the structure are also explained by the coupled mode theory (CMT) and standing wave theory. For further research, inverting ETSC could dramatically increase quality factor to enhance resonance wavelength selectivity. After that, a bar is introduced into the ETSC and the inverted ETSC to increase resonance wavelengths through changing the structural parameters of the bar. In addition, working as a highly efficient narrowband filter, this structure owes a good sensitivity (S = 923 nm/RIU) and a pretty high-quality factor (Q = 322) along with a figure of merit (FOM = 710). Additionally, a narrowband peak with 1.25 nm Full-Width-Half-Maximum (FWHM) can be obtained. This structure will be used in highly integrated optical circuits in future.
Highlights
Surface plasmon polaritons (SPPs) perform as special electromagnetic (EM) waves that propagate along with the metal–dielectric interface and decay exponentially in the perpendicular direction [1]
Visible and near-infrared resonance wavelengths can be controlled via changing the geometrical parameters of bar
On the other hand, inverting the equilateral triangle-shaped cavity (ETSC) results in quality factors of all resonance wavelengths increasing dramatically with peak at 322, and FWHM decreasing significantly with minimum at 1.25 nm when λr = 413 nm
Summary
Surface plasmon polaritons (SPPs) perform as special electromagnetic (EM) waves that propagate along with the metal–dielectric interface and decay exponentially in the perpendicular direction [1]. Because of their outstanding properties, such as overcoming the conventional optical diffraction limit [3] and achieving the transmission and manipulation of the optical signal within the subwavelength scale [4] Under these characteristics, SPPs are widely used among optical communication, physical chemistry, biological and biochemical sensing [5,6], etc. Guatha et al detected biomonolayers and streptavidin-conjugated semiconducting quantum dots by employing the arrays of gold nanoantennas covered by an ultrathin silicon layer. They found surface lattice resonances (SLRs) with high sensitivities to small changes of refractive index [10]. Liping Huang et al employed a spike protein specific nanoplasmonic resonance sensor to measure SARS-CoV-2 virus particle with only one step [12]
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