MDM波导耦合M型谐振腔的折射率传感性能

doi:10.19596/j.cnki.1001-246x.8828

摘要/Abstract

摘要：

提出一种金属-电介质-金属(MDM)波导侧向耦合M型谐振腔实现高灵敏度折射率传感的等离激元波导结构。采用有限元分析法定量分析谐振腔结构参数及填充介质折射率对MDM波导透射谱线的定量影响。仿真结果显示: M型腔中的一到四阶类法布里-珀罗(FP)谐振模式与MDM主波导中金属挡板产生的反射导波模式进行耦合干涉形成四重Fano共振透射峰。该透射峰不仅具有非对称谱线形状及陡峭边沿分布, 而且峰值波长随腔长及填充媒质折射率的改变呈现近似线性变化的规律。选取长宽为400 nm×400 nm的M型谐振腔可以产生最高灵敏度为4 900 nm/RIU的一阶Fano共振透射峰。计算结果显示: 传感灵敏度与谐振腔长成正比及与谐振阶次成反比的变化规律, 为高灵敏度传感器的设计提供参考。

关键词: 表面等离激元, MDM波导, M型腔, Fano共振, 有限元法

Abstract:

A high sensitivity refractive index sensor have been proposed in this paper, which is composed by an M-shaped resonant cavity coupled with a baffle contained Metal-Dielectric-Metal (MDM) waveguide. The influence of structural parameter of M-shaped cavity and filled medium characteristics inside it on the transmission spectrum of MDM waveguide have been analyzed numerically through the finite element method. Simulation results show that four asymmetric transmission peaks with Fano line-shape are generated by the coupling interference between the four quasi Fabry-Perot (FP) resonant modes of the first to fourth orders inside M-shaped cavity and the reflected wave in MDM waveguide, moreover the four peak wavelengths redshift almost linearly with increasing cavity length or the refractive index of the filled medium, which can be used to design the refractive index sensor. The calculated sensitivities associated with the quadruple Fano transmission peaks are found to be proportional to the cavity length and the reciprocal of resonant order. As a consequence, a sensitive up to 4 900 nm/RIU has been realized by an M-shaped resonator in dimensions of 400 nm×400 nm. The results in the article provide an effective guidance for the design of high sensitivity sensors.

Key words: surface plasmon polaritons, metal-dielectric-metal waveguide, M-shaped resonator, Fano resonance, finite element method

许蒲城, 关建飞. MDM波导耦合M型谐振腔的折射率传感性能[J]. 计算物理, 2025, 42(1): 57-64.

Pucheng XU, Jianfei GUAN. Analysis of Refractive Index Sensing Performance of MDM Waveguide Coupled with an M-shaped Resonant Cavity[J]. Chinese Journal of Computational Physics, 2025, 42(1): 57-64.

图/表 8

图1 含挡板MDM波导耦合M型谐振腔结构

Fig.1 Schematics of MDM waveguide side-coupled with M-shaped cavity

图2 含挡板MDM波导结构的透射谱线

Fig.2 Transmission spectra of MDM waveguide system

图3 四重透射峰值对应的磁场Hz强度分布图 (a) λ=1 018 nm; (b)λ=1 387 nm; (c)λ=2 042 nm; (d)λ=4 075 nm

Fig.3 Magnetic field distributions corresponding to quadruple transmittance extrema in blue transmission spectra shown in Fig. 2 (a) λ=1 018 nm; (b)λ=1 387 nm; (c)λ=2 042 nm; (d)λ=4 075 nm

图4 M型腔高度S1对透射谱线的影响(a)不同S1值对应的透射谱线; (b) Fano共振峰波长与S1的关系

Fig.4 Transmission characteristics of MDM waveguide coupled with M-shaped cavity with heights S1 (a) transmission spectra with S1; (b) linear fitting between the resonant wavelengths and S1

图5 M型腔横向宽度a对透射谱线的影响(a) 不同a值对应的透射谱；(b) Fano谐振波长与a的关系

Fig.5 Transmission characteristics of MDM waveguide coupled with the M-shaped cavity with widths a(a) transmission spectra with a; (b) linear fitting between the resonant wavelengths and a

图6 不同耦合间距g下的透射特性(a)透射谱线; (b)峰值半高宽; (c)透射峰Q

Fig.6 Transmission characteristics of the MDM waveguide system with g (a) transmission spectrums; (b) transmittance peaks' FWHM; (c) evolution of Q

图7 边长S1=350 nm, a=50 nm的M型腔内介质折射率对透射谱线的影响(a)不同介质折射率产生的透射谱线; (b)峰值波长与介质折射率n的关系; (c)透射峰的灵敏度及FOM值

Fig.7 Transmission characteristics of MDM waveguide coupled with M-shaped resonator with S1=350 nm and a=50 nm for deferent refractive indexes n (a) transmission spectra for five different refractive indexes n; (b) linear fitting between resonant wavelengths and refractive indexes n; (c) evolution of sensitivity and FOM with resonant order

图8 边长S1=400 nm, a=100 nm的M型腔内介质折射率对透射谱线的影响(a) 不同介质折射率产生的透射谱线；(b) 峰值波长与介质折射率n的关系；(c) 透射峰的灵敏度及FOM值

Fig.8 Transmission characteristics of the MDM waveguide coupled with an M-shaped resonator with S1=400 nm and a=100 nm for deferent refractive indexes n (a) transmission spectra for five different refractive indexes n; (b) linear fitting between the resonant wavelengths and refractive indexes n; (c) evolution of sensitivity and FOM with resonant order

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