Abstract
In this paper, we provide a detailed three-dimensional numerical analysis of the optical properties of common and modified bowtie aperture antennas integrated onto a silicon waveguide platform, to discuss the influence of geometrical parameters on the electric field enhancement factor and waveguide transmission when such antennas are excited by the evanescent field of the Si waveguide mode. We demonstrate that waveguide transmission is severely affected by the interference between Si waveguide modes and surface plasmon polariton modes excited in the antenna, while the antenna's field enhancement factor is mainly determined by the localized surface plasmon resonance occurring in its nano-gap. These mechanisms lead to a mismatch between the wavelength at which the antenna's field enhancement factor is maximized, and the wavelength at which transmission through the Si waveguide is minimized, suggesting that in some multi-mode cases, the optical properties of integrated nanoantennas determined through direct measurement of Si waveguide transmission may be misleading. Methods for improving the electric field enhancement (such that it has a bigger modulation depth) that have minimal impact on the resonant wavelength, and for improving the shape and location of the corresponding hot spot of the bowtie aperture antennas, are also discussed and analyzed. We believe that this analysis will be helpful in design of on-chip bowtie-type optical antennas for surface enhanced Raman spectroscopy, near-field optical microscopy, high sensitivity detection, and plasmonic optical tweezers.
Highlights
By enabling the concentration of electromagnetic radiation to sub-wavelength scales to produce extremely strong and highly localized electromagnetic fields, metal nanoparticles and nanostructures have the ability to break the diffraction limit, which has attracted widespread attention from many researchers attempting to explore potential applications of this phenomenon [1]–[3]
In this paper, we provide a detailed three-dimensional numerical analysis of the optical properties of common and modified bowtie aperture antennas integrated onto a silicon waveguide platform, to discuss the influence of geometrical parameters on the electric field enhancement factor and waveguide transmission when such antennas are excited by the evanescent field of the Si waveguide mode
We demonstrate that waveguide transmission is severely affected by the interference between Si waveguide modes and surface plasmon polariton modes excited in the antenna, while the antenna’s field enhancement factor is mainly determined by the localized surface plasmon resonance occurring in its nano-gap
Summary
By enabling the concentration of electromagnetic radiation to sub-wavelength scales to produce extremely strong and highly localized electromagnetic fields (known as “hot spots”), metal nanoparticles and nanostructures have the ability to break the diffraction limit, which has attracted widespread attention from many researchers attempting to explore potential applications of this phenomenon [1]–[3]. Optical antennas exploit the unique properties of metal nanostructures that exhibit strong coupling of electronic plasma to electromagnetic radiation at optical frequencies These antennas can direct electromagnetic waves in sub-wavelength-scale devices, for applications such as near-field optical microscopy [20]–[23], surface-enhanced Raman spectroscopy [13]–[17], [24], surface enhanced infrared absorption spectroscopy [25], [26], and photovoltaics [27], and devices such as nanoLEDs [28], [29]. The change in the waveguide’s transmission and field enhancement factor are subsequently used to analyze the relationship between the optical and geometric properties of the antenna
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