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Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending

Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending
Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending
All-dielectric, phase-gradient metasurfaces manipulate light via a judiciously designed planar distribution of high and low refractive indices. In the established design approaches, the high-index elements play a dominant role, while the electromagnetic field existing between these elements is routinely viewed as either an incidental by-product or detrimental crosstalk. Here we propose an alternative approach that concentrates on exploring the low-index materials for wavefront shaping. In our Si metasurface, the low-index air gap between adjacent Si fins is judiciously tuned, while the high-index Si fins only have a single size across the whole metasurface. These gap modes provide the full 2π phase coverage, as well as high and relatively uniform transmission, at the deep-subwavelength scale. These characteristics are ideal for mapping a steep phase gradient, consequently suitable for high-efficiency and large-angle wavefront bending. This light manipulation capability is exemplified with numerical simulation in PW-SW (freely propagating wave to surface wave) conversion, where the wavefront is deflected by an angle of 90°. In the gap-mode meta-converters, the average unit size can be only 1/60 of free-space wavelength, an order of magnitude smaller than that of conventional all-dielectric metasurfaces. Their conversion efficiency can reach 68%, the highest value reported for any all-dielectric gradient metasurface THz converter.
1094-4087
12080-12091
Lyu, Wen
e8760cff-7838-4e84-b76e-07337f0619ee
Liu, Jiaming
1fad0248-35f1-4613-a32f-c319a11835ce
Yin, Shengqi
363a868e-95cb-4354-b52f-0d4f9fcd3e70
Deng, Xiaojiao
ccb9674c-95f0-43cb-b09b-5af200c85318
Fang, Xu
96b4b212-496b-4d68-82a4-06df70f94a86
Geng, Hua
4de0000a-a809-4b66-81bb-ea0befdad671
Zheng, Xiaoping
81475ce2-f9d2-4173-81de-b95083c90b29
Lyu, Wen
e8760cff-7838-4e84-b76e-07337f0619ee
Liu, Jiaming
1fad0248-35f1-4613-a32f-c319a11835ce
Yin, Shengqi
363a868e-95cb-4354-b52f-0d4f9fcd3e70
Deng, Xiaojiao
ccb9674c-95f0-43cb-b09b-5af200c85318
Fang, Xu
96b4b212-496b-4d68-82a4-06df70f94a86
Geng, Hua
4de0000a-a809-4b66-81bb-ea0befdad671
Zheng, Xiaoping
81475ce2-f9d2-4173-81de-b95083c90b29

Lyu, Wen, Liu, Jiaming, Yin, Shengqi, Deng, Xiaojiao, Fang, Xu, Geng, Hua and Zheng, Xiaoping (2022) Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending. Optics Express, 30 (7), 12080-12091. (doi:10.1364/OE.455113).

Record type: Article

Abstract

All-dielectric, phase-gradient metasurfaces manipulate light via a judiciously designed planar distribution of high and low refractive indices. In the established design approaches, the high-index elements play a dominant role, while the electromagnetic field existing between these elements is routinely viewed as either an incidental by-product or detrimental crosstalk. Here we propose an alternative approach that concentrates on exploring the low-index materials for wavefront shaping. In our Si metasurface, the low-index air gap between adjacent Si fins is judiciously tuned, while the high-index Si fins only have a single size across the whole metasurface. These gap modes provide the full 2π phase coverage, as well as high and relatively uniform transmission, at the deep-subwavelength scale. These characteristics are ideal for mapping a steep phase gradient, consequently suitable for high-efficiency and large-angle wavefront bending. This light manipulation capability is exemplified with numerical simulation in PW-SW (freely propagating wave to surface wave) conversion, where the wavefront is deflected by an angle of 90°. In the gap-mode meta-converters, the average unit size can be only 1/60 of free-space wavelength, an order of magnitude smaller than that of conventional all-dielectric metasurfaces. Their conversion efficiency can reach 68%, the highest value reported for any all-dielectric gradient metasurface THz converter.

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Accepted/In Press date: 17 March 2022
Published date: 28 March 2022
Additional Information: Funding Information: National Natural Science Foundation of China (61927804); Royal Society (IEC\R3\183071, IES\R3\183086). Publisher Copyright: © 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Identifiers

Local EPrints ID: 456421
URI: http://eprints.soton.ac.uk/id/eprint/456421
ISSN: 1094-4087
PURE UUID: 4ee76036-65cb-494e-b300-261136764db8
ORCID for Xu Fang: ORCID iD orcid.org/0000-0003-1735-2654

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Date deposited: 28 Apr 2022 16:41
Last modified: 29 Apr 2022 01:44

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Contributors

Author: Wen Lyu
Author: Jiaming Liu
Author: Shengqi Yin
Author: Xiaojiao Deng
Author: Xu Fang ORCID iD
Author: Hua Geng
Author: Xiaoping Zheng

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