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Photonics 2019, 6(1), 26; https://doi.org/10.3390/photonics6010026

The Design of Optical Circuit-Analog Absorbers through Electrically Small Nanoparticles

1
Department of Engineering, Niccolò Cusano University, Via don Carlo Gnocchi 3, 00166 Rome, Italy
2
CUNY Advanced Science Research Center, 85 St. Nicholas Terrace, New York, NY 10031, USA
3
Department of Engineering, Roma Tre University, Via Vito Volterra 62, 00146 Rome, Italy
*
Author to whom correspondence should be addressed.
Received: 5 February 2019 / Revised: 28 February 2019 / Accepted: 28 February 2019 / Published: 6 March 2019
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Abstract

In the last few years, the perfect absorption of light has become an important research topic due to its dramatic impact in photovoltaics, photodetectors, color filters and thermal emitters. While broadband optical absorption is relatively easy to achieve using bulky devices, today there is a strong need and interest in achieving the same effects by employing nanometric structures that are compatible with modern nanophotonic components. In this paper, we propose a general procedure to design broadband nanometer-scale absorbers working in the optical spectrum. The proposed devices, which can be considered an extension to optics of microwave circuit-analog absorbers, consist of several layers containing arrays of elongated nanoparticles, whose dimensions are engineered to control both the absorption level and the operational bandwidth. By combining a surface-impedance homogenization and an equivalent transmission-line formalism, we define a general analytical procedure that can be employed to achieve a final working design. As a relevant example, we show that the proposed approach allows designing an optical absorber exhibiting a 20% fractional bandwidth on a thickness of λ/4 at the central frequency of operation. Full-wave results confirming the effectiveness of the analytical findings, as well as some considerations about the experimental realization of the proposed devices are provided. View Full-Text
Keywords: nanoparticles; optical losses; circuit-analog absorbers; surface dispersion effect; plasmonics nanoparticles; optical losses; circuit-analog absorbers; surface dispersion effect; plasmonics
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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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Monti, A.; Alù, A.; Toscano, A.; Bilotti, F. The Design of Optical Circuit-Analog Absorbers through Electrically Small Nanoparticles. Photonics 2019, 6, 26.

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