High sensitivity plasmonic refractive index and temperature sensor based on square ring shape resonator with nanorods defects

A high sensitivity plasmonic temperature sensor via a metal–insulator–metal (MIM) waveguide system is presented in this paper, the waveguide structure is composed of a square ring shape resonator with nanorods defects and a nanodisk resonator. Finite difference-time domain method (FDTD) is used to study the structure’s transmission characteristics and electromagnetic field distributions. Results show that sensitivity will be increased due to the gap plasmonic in the nanorod defect, the nanodisk resonator provides more plasmonic resonant modes for sensing. The positions and intensities of plasmonic resonant modes can be tuned by the radius of nanorod defects and coupling distance. The calculated maximum refractive index sensitivity and figure of merit (FOM) are 4265nm/RIU\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${4265}\;{\text{nm/RIU}}$$\end{document}(RIU is refractive index unit) and 3500 RIU-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{RIU}}^{ - 1}$$\end{document}, respectively. Compared to the structure without nanorods, the sensitivity is enhanced 33% for mode 1. For temperature sensing, the proposed structure possesses a relatively high sensitivity of about 1.2 nm/°C in the range of −100 to 60 °C. The proposed plasmonic structure provides a basis for designing high sensitivity nano-biosensing, refractive index sensing.