Near-field phase characterization of gradient gap plasmon-based metasurfaces

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Abstract

Metasurface studies have demonstrated vast applications to control optical properties of light based on the ability to design unit cells with desired phase and reflectivity in 2D subwavelength periodic arrays. The simplified design strategy is only an approximation since the unit cells can be subject to near-field coupling effects due to influence from neighbor unit cells. In this work, we try to investigate this effect by numerically and experimentally studying the near-field response from gold nanobricks of varied length, fabricated in both quasi-periodic and periodic configuration on top of dielectric-coated (SiO2) layer and gold layer at telecommunication wavelength (1500 nm), which is the commonly used gap plasmon configuration for efficient metasurfaces. The experimental near-field investigation is performed using a phase-resolved scattering-type scanning near-field optical microscopy (s-SNOM) in the transmission mode. We demonstrate that near-field coupling becomes significant when edge-to-edge separation between GSP elements goes below ∼200-250 nm. We also show that the reflection phase of any GSP element is approximately equal to its doubled near-field phase. Thus, our studies provide a direct explanation of a reduced performance of a densely-packed GSP metasurfaces. This technique can accurately predict the performance of different types of metasurfaces by observing their near-field response in different periodic configurations by considering factors ignored in the design stage, which include fabrication uncertainties, wrong design considerations along with near-field coupling effects.

Original languageEnglish
Title of host publicationProceedings of SPIE Photonics Europe : Metamaterials XI
EditorsAnatoly V. Zayats, Allan D. Boardman, Kevin F. MacDonald
Volume10671
PublisherSPIE - International Society for Optical Engineering
Publication dateMay 2018
Article number1067129
ISBN (Electronic)9781510618688
DOIs
Publication statusPublished - May 2018
EventSpie Photonics Europe - Strasbourg, France
Duration: 22. Apr 201826. Apr 2018

Conference

ConferenceSpie Photonics Europe
Country/TerritoryFrance
CityStrasbourg
Period22/04/201826/04/2018
SponsorCNRS - The National Center for Scientific Research, et al., iCube, Investissements d'Avenvir, Strasbourg the Europtimist, The Society of Photo-Optical Instrumentation Engineers (SPIE)
SeriesProceedings of SPIE, the International Society for Optical Engineering
ISSN0277-786X

Keywords

  • gap surface plasmons
  • metasurfaces
  • Near-field
  • s-SNOM

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