Abstract
Using a single interferometric lithography patterning step along with self-aligned pattern-definition techniques, uniform, large-area metallic coaxial arrays with ~ 100-nm toroidal gaps are fabricated. Enhanced (5x) mid-infrared (4 mum) transmission through these sub-wavelength coaxial arrays is observed as compared with that through the same fractional opening area hole arrays as a result of the complex coaxial unit cell. Varying the coaxial dimensions shifts the resonance wavelength and impacts the maximum transmission; design rules are derived. The ability to control the transmission wavelength combined with dramatically enhanced transmission represent a promising path toward nanophotonic applications.
Highlights
Improvements in fabrication capabilities for metallic nanostructures have led to intense interest in a broad range of applications
From the TE and TM polarization angle-dependent data of metallic coaxial arrays presented here, we reconfirm that the surface plasmons are responsible for the enhanced transmission observed in metallic hole arrays, and that with a coaxial aperture rather than a simple hole significantly enhanced transmission can be achieved
The sub-wavelength scale of these structures will lead to applications in photonic circuits and the localization of the light in the apertures provides an electric-field enhancement that can be used to manipulate light-matter interactions and enhance nonlinear phenomena [7,8]
Summary
Improvements in fabrication capabilities for metallic nanostructures have led to intense interest in a broad range of applications. From the TE and TM polarization angle-dependent data of metallic coaxial arrays presented here, we reconfirm that the surface plasmons are responsible for the enhanced transmission observed in metallic hole arrays, and that with a coaxial aperture rather than a simple hole significantly enhanced transmission can be achieved. Arrays of coaxial metallic structures, first proposed by Baida et al [9,10], support additional guided electromagnetic modes and have substantially greater transmission and correspondingly larger field enhancements than do simple hole arrays. By using rigorous coupled-wave analysis (RCWA) simulation as design guide to arrange the spectral overlap between the coaxial transmission peak and the SP peak, a 5× enhanced mid-infrared (4 μm) transmission through these sub-wavelength coaxial arrays is realized as compared with that through hole arrays with the same fractional open area
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