Abstract
Cylindrical waveguides have a wide range of applications in photonic integrated circuits because of lower transmission losses. This paper proposes a directional coupler composed of a cylindrical silicon nanowire waveguide and a metal-based cylindrical hybrid plasmon waveguide. The coupling characteristics of the coupler are analyzed theoretically and are also simulated using the finite-difference time-domain method. The results show that the coupler can operate effectively with a relatively short coupling length, displaying low insertion loss, and a high coupling efficiency and extinction ratio. This study also shows how the TM mode in the plasmon waveguide can be excited with the TE mode of the dielectric waveguide. This directional coupler has a potential application in signal exchanging and mode switching between the dielectric and plasmon waveguides in photonic integrated circuits.
Highlights
Surface plasmon polaritons (SPPs),1 which propagate along a conductor–dielectric interface, exhibit a strong electromagnetic (EM) confinement property far beyond the diffraction limit of light
Conventional dielectric-based devices exhibit the opposite characteristics with poor EM confinement and low losses due to absorption
Integrating SPP-based and dielectricbased photonic devices on the same chip platform offers the opportunity to offset the individual deficiencies in each type of photonic device, assuming that EM field transmission and signal exchange can efficiently be achieved between them
Summary
Surface plasmon polaritons (SPPs), which propagate along a conductor–dielectric interface, exhibit a strong electromagnetic (EM) confinement property far beyond the diffraction limit of light. This feature has attracted much interest in the development of promising applications in photonic integrated circuits, such as filtering, guiding waves, absorbing, and sensing.. By coupling the EM field between the dielectric and plasmon waveguides, energy transmission and signal exchange can be achieved for them. A range of directional couplers have been proposed, which can effectively transfer the EM field from dielectric waveguides to plasmon waveguides. Much research is needed to explore how the EM energy can be transferred using different directional couplers based on the various shape types. This work provides a method to excite the TM mode in the plasmon waveguide with the TE mode of the dielectric waveguide
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