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Photonics
Volume 13
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10.3390/photonics13010034
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Article

Plasmonic Sensor Based on an MIM Waveguide Coupled with a Ring–Bridge–Rounded Square Resonator

by
Weixin Liu
1,2,3,
Shubin Yan
2,3,*,
Zhenyang Xu
4,
Yang Cui
2,3,
Biyi Huang
2,3,
Guang Liu
2,3,
Di Zheng
1 and
Taiquan Wu
2,3
1
College of Mechanical and Electrical Engineering, China Jiliang University, Hangzhou 310018, China
2
School of Electrical Engineering, Zhejiang University of Water Resources and Electric Power, Hangzhou 310018, China
3
Joint Laboratory of Intelligent Equipment and System for Water Conservancy and Hydropower Safety Monitoring of Zhejiang Province and Belarus, Hangzhou 310018, China
4
School of Geomatics, Zhejiang University of Water Resources and Electric Power, Hangzhou 310018, China
*
Author to whom correspondence should be addressed.
Photonics 2026, 13(1), 34; https://doi.org/10.3390/photonics13010034 (registering DOI)
Submission received: 10 December 2025 / Revised: 27 December 2025 / Accepted: 29 December 2025 / Published: 30 December 2025
Versions Notes

Abstract

Fano resonance sensors based on metal–insulator–metal (MIM) waveguides often face the challenge of balancing high sensitivity (S) and a high figure of merit (FOM). In this work, a high-performance refractive index sensor is proposed, consisting of a straight MIM waveguide side-coupled to a novel ring–bridge–rounded square (RBS) resonator. The transmission characteristics and the formation mechanism of Fano resonance are systematically analyzed using the finite element method (FEM). The results demonstrate that the synergistic introduction of rounded square units and an internal bridge structure significantly enhances electromagnetic field localization and optimizes the coupling strength. The optimized device achieves a remarkable refractive index sensitivity of 3268 nm/RIU (refractive index unit, RIU) and a high FOM of 55.4. Furthermore, by employing ethanol as the filling medium, the proposed configuration functions as a temperature sensor, exhibiting a high linear sensitivity of 1.644 nm/°C over the range of –70 °C to 70 °C. The proposed RBS resonator holds promise for compact and high-precision nanophotonic sensing applications.
Keywords: surface plasmon polaritons; metal–insulator–metal (MIM) waveguide; fano resonance; refractive index sensor surface plasmon polaritons; metal–insulator–metal (MIM) waveguide; fano resonance; refractive index sensor

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MDPI and ACS Style

Liu, W.; Yan, S.; Xu, Z.; Cui, Y.; Huang, B.; Liu, G.; Zheng, D.; Wu, T. Plasmonic Sensor Based on an MIM Waveguide Coupled with a Ring–Bridge–Rounded Square Resonator. Photonics 2026, 13, 34. https://doi.org/10.3390/photonics13010034

AMA Style

Liu W, Yan S, Xu Z, Cui Y, Huang B, Liu G, Zheng D, Wu T. Plasmonic Sensor Based on an MIM Waveguide Coupled with a Ring–Bridge–Rounded Square Resonator. Photonics. 2026; 13(1):34. https://doi.org/10.3390/photonics13010034

Chicago/Turabian Style

Liu, Weixin, Shubin Yan, Zhenyang Xu, Yang Cui, Biyi Huang, Guang Liu, Di Zheng, and Taiquan Wu. 2026. "Plasmonic Sensor Based on an MIM Waveguide Coupled with a Ring–Bridge–Rounded Square Resonator" Photonics 13, no. 1: 34. https://doi.org/10.3390/photonics13010034

APA Style

Liu, W., Yan, S., Xu, Z., Cui, Y., Huang, B., Liu, G., Zheng, D., & Wu, T. (2026). Plasmonic Sensor Based on an MIM Waveguide Coupled with a Ring–Bridge–Rounded Square Resonator. Photonics, 13(1), 34. https://doi.org/10.3390/photonics13010034

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