Resonance of Different Waveguide Structures with Various Vertical Indirect Coupled Cavities
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Resonance of Different Waveguide Structures with Various Vertical Indirect Coupled Cavities Shu Li1 · Shu‑Guang Chen1 · Shi‑Fang Xiao1 · Huang‑Qing Liu1 · Jing‑Jing Mao2 · Jian‑Zhong Mao3 Received: 5 August 2020 / Accepted: 13 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In the paper, resonances of different waveguide structures with various vertical indirect coupled cavities were investigated by FDTD (finite difference-time domain). In the silicon cavity, Fano resonance could be observed at about 1430 nm. The coupling distance for the gold cavity/air cavity had less effect on the transmittance of the main waveguide but had a great influence on the transmission for water cavity in the visible region, which showed that water cavity could adjust resonance of waveguide structures. In addition, with the increment of refractive index n, the resonance peak at about 850 nm moved to the long wavelength (redshift). Dispersion rate about 2 × 10–3/nm indicated that the transparent dielectric selectively absorbed the surface plasmon polariton wave and the sensitivity of the waveguide structure designed in this paper has high stability for the refractive index of the main waveguide cavity. Obvious Fano resonance could be observed with the increase of refractive index for silicon cavity. Among the four dielectrics, silicon and water are suitable for studying Fano resonance and filter dielectrics. Keywords Fano resonance · Different waveguide structures · FDTD · Indirect coupled cavities
Introduction Owing to their interaction between the free electrons in metals and photons, surface plasmons (SPs) [1, 2] can confine and propagate the electromagnetic energy in a subwavelength limit. So far, a lot of related research on the SP polaritons (SPPs) has been reported [3–6]. Many nanostructures were designed for guiding SPPs, such as trench waveguides [7] and photonic bandgap waveguides [8]. The metal–insulator–metal (MIM) waveguide [9–12] is very popular with researchers because of its attractive features and extensive applications. In the nano-photonic circuits, MIM waveguides can reduce energy loss in the process of light propagation. As a result, various functional plasmonic devices based on MIM waveguides have been proposed and
* Huang‑Qing Liu [email protected] 1
School of Physics and Electronics, Hunan University, Changsha 410082, China
2
HuaiHua Teachers College, Huaihua 418000, China
3
College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, China
experimentally examined [13–16]. The most common structures for the plasmonic filters are MIM waveguides coupled with a rectangular cavity [17–20], a ring cavity [21], a the coupled fillet cavity [22]. There were more researches on the Fano resonance of silicon as the dielectric in the coupling cavity of MIM waveguides [22, 30]. Due to the relatively large dielectric constant and high-order resonance in the near-infrared region, silicon is usually regarded as the discrete state of Fano resonance
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