Degenerate Coupled Mode Division and Superposition Under Symmetry Breaking
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Degenerate Coupled Mode Division and Superposition Under Symmetry Breaking Fa‑Xiu Chen1 · Yue‑Gang Chen1 Received: 14 August 2020 / Accepted: 13 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Resonances in micrometer metal cavity structures are very important for the interactions between materials and light. Three similar cavities connected with waveguides are investigated through the finite difference time domain (FDTD) method and the coupled mode theory. Two fundamental surface resonance modes are demonstrated in the two simple cavities separately. Then two simple cavities are combined to form the third cavity. The fundamental resonant modes couple positively or oppositely to form coupled-mode resonances in the combined cavity. When the combined cavity structures are symmetric, the coupled-mode resonances lead to two transmission peaks. While the symmetry is broken with tens of nanometers displacements, the transmission peaks convert to dips. It is believed the Q value variation of coupled-mode resonances plays a key role in the conversion. When the structure is symmetric, the coupled-mode resonances in the upper and lower parts of the cavity have the same Q value and are degenerate. The superposition of them leads transmission peaks. While the symmetry is broken, the Q values of resonances in the upper and lower part of the cavity are different, leading to the degenerate coupled mode division. The superposition of the different Q-factor modes leads to the dips. The sensitive variation to the symmetry of structures can be used to control light-material interactions, optical switch, and improve the sensitivity of sensor devices. Keywords Surface plasmons · Nanostructure fabrication · Optical resonator
Introduction Surface plasmon (SP) is the electromagnetic resonance, which contributes to the electron resonances on metal surface [1, 2]. Many interesting phenomena due to SP resonances (SPRs) appear in metal micro-nanometre structures, such as enhanced transmission through subwavelength holes [3], Fano resonances [4, 5, 6, 7], nonlinear optical effects enhancement [8], and Wood’s anomaly [9]. There are bright and dark SPR modes in metal micronano meter structures. The bright SPR modes with wide spectrum can couple with incident light, while the dark SPR modes with narrow spectrum cannot couple directly with
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11468-020-01311-7) contains supplementary material, which is available to authorized users. * Yue‑Gang Chen [email protected] 1
School of Physics, Guizhou University, Guiyang 550025, Guizhou, China
incident waves. The efficient coupling between dark SPR modes in antenna can be excited by the evanescent field of waveguide [10]. In the nano-antennas made of two identical plasmonic slot resonators, bright and dark SPR modes can be selectively excited with an incident plane wave through modulating the phase between the two antennas, and brightto-dark SPR mode conver
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