A Novel Plasmonic Zone Plate Lens Based on Nano-Slits with Refractive Index Modulation |
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Authors: | Qin Chen |
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Institution: | (1) School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow, G12 8LT, UK |
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Abstract: | Conventionally, plasmonic lenses introduce a phase delay distribution across their surfaces by modulating the dimensions of
nanostructures within a metal film. However, there is very limited modulation of the phase delay due to the small dependence
of the mode propagation constant on the structure dimensions. In this paper, a novel design of plasmonic zone plate lenses
(PZPL) with both slit width and refractive index modulation is proposed to enable integrating more slits in a fixed lens aperture
with the extended phase delay range and, therefore, greatly enhance the performance of the devices. More than three-time enhancement
of the light intensity at the focus is achieved compared to the structure with only slit width modulation. Like a conventional
immersion system, a PZPL embedded in a dielectric is found to have a further improved focusing performance, where light is
focused down to a 0.44λ spot using a PZPL with an aperture of 12λ and a focal length of 6λ. Dispersive light-focusing behaviour is also analysed and the modulation of the focal length by colour has a potential application
in stacked image sensors and multi-dimensional optical data storage. |
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Keywords: | |
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