Abstract
Multiple resonance modes have important applications since they can provide multi-frequency operation for devices and bring great flexibility in practice. In this paper, based on a fan-shaped cavity coupled to a metal-isolator-metal (MIM) waveguide, a new kind of ultracompact plasmonic nanostructure is proposed to realize multiple resonance modes with dense distribution in a broad spectral range, and demonstrated through finite-element method (FEM) simulations. As many as ten resonance modes with an average interval of about 30 nm are obtained. They originate from the coexistence and interference of three types of basic modes in the fan-shaped cavity, i.e., the ring-waveguide modes, the modes in a ring array of periodic air grooves, and the metal-core-cavity modes. The dependence of resonance modes on structure parameters is investigated, which can provide an effective guide for choosing appropriate multiple-resonance-mode structures. Furthermore, by means of adjusting the geometrical asymmetry induced by the axial offset of the metal core in the fan-shaped cavity, the resonance modes can be effectively modulated, and some new modes appear because the wave path in the cavity is changed. The result proposes a novel way to create multiple resonance modes in plasmonic nanostructures, providing additional degrees of freedom for tailoring the resonance spectra and promising applications in various plasmonic devices, such as optical filters, ultrafast switches, biochemical sensors, and data storages.
Highlights
Surface plasmon polaritons (SPPs) are electromagnetic waves propagating along metal-dielectric interfaces and decaying drastically along the vertical direction of metal surfaces, generated through the interaction between incident light and free electrons in metal [1–5]
Plasmonic devices with multiple resonance modes have attracted great research interest since they are very useful in applications that need to be operated at different frequencies
In order to input and output electromagnetic waves, a MIM straight waveguide was side-coupled to the fan-shaped cavity with the width W = 70 nm to ensure that only the fundamental transverse magnetic (TM) mode was supported
Summary
Surface plasmon polaritons (SPPs) are electromagnetic waves propagating along metal-dielectric interfaces and decaying drastically along the vertical direction of metal surfaces, generated through the interaction between incident light and free electrons in metal [1–5]. Much attention has been devoted to SPP structures since they have many attractive capabilities, such as overcoming the optical diffraction limit, forming strongly localized fields on metal-dielectric surfaces, and manipulating light at nanoscale [6–13]. The main method to obtain plasmonic multimodes is to cascade several identical or similar (stretching or shrinking the scale of the size with the configuration unchanged) resonance elements, such as T-typed waveguides, nanodisk cavities, or rectangular resonators [22–29]. Three kinds of different elements were selected, i.e., the ring waveguide, the ring array of periodic metal-air grooves, and the metal-core circular cavity, to form a fan-shaped cavity. In order to input and output electromagnetic waves, a MIM straight waveguide was side-coupled to the fan-shaped cavity with the width W = 70 nm to ensure that only the fundamental transverse magnetic (TM) mode was supported. The structure surrounded by perfectly matched layers was divided into about 6.5 × 104 cell grids to ensure the accuracy of calculation
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