Significantly enhanced coupling effect and gap plasmon resonance in a MIM-cavity based sensing structure

Yuan-Fong Chou Chau,Hung Ji Huang,Chung-Ting Chou Chao,Muhammad Raziq Rahimi Kooh,Roshan Thotagamuge,Hai-Pang Chiang,Chee Ming Lim,Tan Yu Ming

doi:10.1038/s41598-021-98001-z

Abstract

Herein, we design a high sensitivity with a multi-mode plasmonic sensor based on the square ring-shaped resonators containing silver nanorods together with a metal–insulator-metal bus waveguide. The finite element method can analyze the structure's transmittance properties and electromagnetic field distributions in detail. Results show that the coupling effect between the bus waveguide and the side-coupled resonator can enhance by generating gap plasmon resonance among the silver nanorods, increasing the cavity plasmon mode in the resonator. The suggested structure obtained a relatively high sensitivity and acceptable figure of merit and quality factor of about 2473 nm/RIU (refractive index unit), 34.18 1/RIU, and 56.35, respectively. Thus, the plasmonic sensor is ideal for lab-on-chip in gas and biochemical analysis and can significantly enhance the sensitivity by 177% compared to the regular one. Furthermore, the designed structure can apply in nanophotonic devices, and the range of the detected refractive index is suitable for gases and fluids (e.g., gas, isopropanol, optical oil, and glucose solution).

Highlights

We design a high sensitivity with a multi-mode plasmonic sensor based on the square ringshaped resonators containing silver nanorods together with a metal–insulator-metal bus waveguide
In case 1, only one available transmittance dip corresponding to an SPP mode at λres = 1376 nm can be observed. This SPP mode is due to the surface plasmon resonance (SPR) and cavity plasmon resonance (CPR) from the coupling effect between the square air ring and the MIM bus waveguide
When the silver nanorods appear in the square air ring, case 2 can generate more SPPs modes because of the enhanced SPR, CPR and gap plasmon resonance (GPR) effects among the silver nanorods, leading to four available SPPs modes at λres = 2188 nm, 1258 nm, 1037 nm, and 820 nm, respectively

Summary

Introduction

We design a high sensitivity with a multi-mode plasmonic sensor based on the square ringshaped resonators containing silver nanorods together with a metal–insulator-metal bus waveguide. This paper scrutinized a multiband plasmonic sensor based on a side-coupled resonator in a MIM-cavity waveguide with the refractive index sensing capability in the near-infrared wavelength range. We found that the structure with double square rings, including silver nanorods, can significantly increase the coupling effect between the bus waveguide and the side-coupled resonator since the resonators enhanced the GPR modes.

Results

Conclusion