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Photonics 2018, 5(4), 56; https://doi.org/10.3390/photonics5040056

Super-Oscillatory Metalens at Terahertz for Enhanced Focusing with Reduced Side Lobes

1
Antennas Group-TERALAB, Universidad Pública de Navarra, Campus Arrosadia, Pamplona 31006, Spain
2
School of Engineering, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK
3
Institute of Smart Cities, Public University of Navarra, 31006 Pamplona, Spain
*
Author to whom correspondence should be addressed.
Received: 27 October 2018 / Revised: 16 November 2018 / Accepted: 29 November 2018 / Published: 5 December 2018
(This article belongs to the Special Issue Terahertz Photonics)
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Abstract

In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high reflection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately −11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations. View Full-Text
Keywords: super-oscillatory lens; metalens; metamaterials; metasurfaces; terahertz; evolutionary algorithm; subwavelength focusing; terahertz focusing super-oscillatory lens; metalens; metamaterials; metasurfaces; terahertz; evolutionary algorithm; subwavelength focusing; terahertz focusing
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Legaria, S.; Pacheco-Peña, V.; Beruete, M. Super-Oscillatory Metalens at Terahertz for Enhanced Focusing with Reduced Side Lobes. Photonics 2018, 5, 56.

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