• Photonics Research
  • Vol. 10, Issue 3, 03000719 (2022)
Alessandro Tuniz1、2、*, Markus A. Schmidt3、4, and Boris T. Kuhlmey1
Author Affiliations
  • 1Institute of Photonics and Optical Science (IPOS), School of Physics, The University of Sydney, NSW 2006, Australia
  • 2The University of Sydney Nano Institute (Sydney Nano), The University of Sydney, NSW 2006, Australia
  • 3Leibniz Institute of Photonic Technology (IPHT Jena), 07745 Jena, Germany
  • 4Abbe Center of Photonics and Faculty of Physics, Friedrich-Schiller-University Jena, 07743 Jena, Germany
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    DOI: 10.1364/PRJ.449067 Cite this Article
    Alessandro Tuniz, Markus A. Schmidt, Boris T. Kuhlmey. Influence of non-Hermitian mode topology on refractive index sensing with plasmonic waveguides[J]. Photonics Research, 2022, 10(3): 03000719 Copy Citation Text show less

    Abstract

    We evaluate the sensing properties of plasmonic waveguide sensors by calculating their resonant transmission spectra in different regions of the non-Hermitian eigenmode space. We elucidate the pitfalls of using modal dispersion calculations in isolation to predict plasmonic sensor performance, which we address by using a simple model accounting for eigenmode excitation and propagation. Our transmission calculations show that resonant wavelength and spectral width crucially depend on the length of the sensing region, so that no single criterion obtained from modal dispersion calculations alone can be used as a proxy for sensitivity. Furthermore, we find that the optimal detection limits occur where directional coupling is supported, where the narrowest spectra occur. Such narrow spectral features can only be measured by filtering out all higher-order modes at the output, e.g., via a single-mode waveguide. Our calculations also confirm a characteristic square root dependence of the eigenmode splitting with respect to the permittivity perturbation at the exceptional point, which we show can be identified through the sensor beat length at resonance. This work provides a convenient framework for designing and characterizing plasmonic waveguide sensors when comparing them with experimental measurements.

    1. INTRODUCTION

    Surface plasmon polariton resonant sensors [1] have found wide-ranging applications, particularly for nanoscale biosensing [2], where they allow label-free optical detection of binding events between molecules (e.g.,  antibodies and antigens [3]), protein interactions [4] or exosomes [5]. The original prism-based geometries such as the Kretschmann [6] and Otto [7] configurations are versatile and precise, but rely on free-space optics and are thus relatively bulky. Surface plasmons lend themselves to extreme confinement of light, which could be implemented in very small footprint devices, motivating extensive research investigating strategies for integrating surface plasmon sensors with chip-based [8,9] and fiber-based [10,11] circuitry.

    Copy Citation Text
    Alessandro Tuniz, Markus A. Schmidt, Boris T. Kuhlmey. Influence of non-Hermitian mode topology on refractive index sensing with plasmonic waveguides[J]. Photonics Research, 2022, 10(3): 03000719
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