Gap plasmon mode of eccentric coaxial metal waveguide

Area of Science:

• Nanophotonics and Plasmonics
• Waveguide Optics
• Electromagnetics

Background:

• Coaxial waveguides are fundamental in guiding electromagnetic waves.
• Plasmonic effects enable subwavelength field confinement.
• Eccentricity in nanostructures can break symmetry and modify optical properties.

Purpose of the Study:

• To analyze the gap plasmon mode in an eccentric coaxial waveguide.
• To investigate the impact of eccentricity on effective index and field localization.
• To explore potential applications in nanophotonics and optical coupling.

Main Methods:

• Analysis using the effective index method.
• Validation with fully-vectorial numerical calculations.
• Consideration of nanostructure geometry and optical wavelengths (4 microm and visible regime).

Main Results:

• Extreme subwavelength field localization observed at the narrowest gap due to gap plasmons.
• Significant increase in the effective index of the lowest-order waveguide mode (e.g., 3.7 for a 2 nm gap, >10 in the visible regime).
• Symmetry-breaking enhances local fields and improves optical coupling.

Conclusions:

• The eccentric coaxial waveguide is a promising candidate for future fabrication and experiments.
• The structure offers enhanced light confinement and optical coupling capabilities.
• This design provides a pathway for developing advanced nanophotonic devices.