Refractive index sensor based on Fano resonance in a ring with a rectangular cavity structure

AbstractIn this paper, a sub-wavelength metal-insulator-metal (MIM) waveguide structure is proposed by using a cross-shape rectangular cavity, of which wings are coupled with two rectangular cavities. Firstly, a cross-shape rectangular cavity is placed between the input and output MIM waveguides. According to the mutual interference between bright and dark modes, three Fano resonant peaks are generated. Secondly, by adding a rectangular cavity on the left wing of the cross shaped one, five asymmetric Fano resonance peaks are obtained. Thirdly, six asymmetric Fano resonance peaks are achieved after adding another cavity on the right wing. Finally, the finite-difference-time-domain (FDTD) method and multimode interference coupled-mode theory (MICMT) are used to simulate and analyze the coupled plasmonic resonant system, respectively. The highest sensitivity of 1 000nm/RIU is achieved.

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Improved Refractive Index-Sensing Performance of Multimode Fano-Resonance-Based Metal-Insulator-Metal Nanostructures

Nanomaterials ◽

10.3390/nano11082097 ◽

2021 ◽

Vol 11 (8) ◽

pp. 2097

Author(s):

Yuan-Fong Chou Chau ◽

Chung-Ting Chou Chao ◽

Siti Zubaidah Binti Haji Jumat ◽

Muhammad Raziq Rahimi Kooh ◽

Roshan Thotagamuge ◽

...

Keyword(s):

Refractive Index ◽

Plasmon Resonance ◽

Fano Resonance ◽

High Sensitivity ◽

Metal Nanostructures ◽

Refractive Index Sensor ◽

Metal Insulator ◽

Wide Range ◽

Metal Insulator Metal ◽

Mode 2

This work proposed a multiple mode Fano resonance-based refractive index sensor with high sensitivity that is a rarely investigated structure. The designed device consists of a metal–insulator–metal (MIM) waveguide with two rectangular stubs side-coupled with an elliptical resonator embedded with an air path in the resonator and several metal defects set in the bus waveguide. We systematically studied three types of sensor structures employing the finite element method. Results show that the surface plasmon mode’s splitting is affected by the geometry of the sensor. We found that the transmittance dips and peaks can dramatically change by adding the dual air stubs, and the light–matter interaction can effectively enhance by embedding an air path in the resonator and the metal defects in the bus waveguide. The double air stubs and an air path contribute to the cavity plasmon resonance, and the metal defects facilitate the gap plasmon resonance in the proposed plasmonic sensor, resulting in remarkable characteristics compared with those of plasmonic sensors. The high sensitivity of 2600 nm/RIU and 1200 nm/RIU can simultaneously achieve in mode 1 and mode 2 of the proposed type 3 structure, which considerably raises the sensitivity by 216.67% for mode 1 and 133.33% for mode 2 compared to its regular counterpart, i.e., type 2 structure. The designed sensing structure can detect the material’s refractive index in a wide range of gas, liquids, and biomaterials (e.g., hemoglobin concentration).

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Sensing Features of the Fano Resonance in an MIM Waveguide Coupled with an Elliptical Ring Resonant Cavity

Applied Sciences ◽

10.3390/app10155096 ◽

2020 ◽

Vol 10 (15) ◽

pp. 5096

Author(s):

Hao Su ◽

Shubin Yan ◽

Xiaoyu Yang ◽

Jing Guo ◽

Jinxi Wang ◽

...

Keyword(s):

Refractive Index ◽

Optical Sensors ◽

Fano Resonance ◽

Resonant Cavity ◽

Refractive Index Sensor ◽

Geometrical Parameters ◽

Elliptical Ring ◽

Metal Insulator Metal ◽

Promising Application ◽

Mim Waveguide

In this article, a novel refractive index sensor composed of a metal–insulator–metal (MIM) waveguide with two rectangular stubs coupled with an elliptical ring resonator is proposed, the geometric parameters of which are controlled at a few hundreds of nanometer size. The transmission feature of the structure was studied by the finite element method based on electronic design automation (EDA) software COMSOL Multiphysics 5.4 (Stockholm, Sweden). The rectangular stub resonator can be thought of as a Fabry–Perot (FP) cavity, which can facilitate the Fano resonance. The simulation results reveal that the structure has a symmetric Lorentzian resonance, as well as an ultrasharp and asymmetrical Fano resonance. By adjusting the geometrical parameters, the sensitivity and figure of merit (FOM) of the structure can be optimized flexibly. After adjustments and optimization, the maximum sensitivity can reach up to 1550 nm/RIU (nanometer/Refractive Index Unit) and its FOM is 43.05. This structure presented in this article also has a promising application in highly integrated medical optical sensors to detect the concentration of hemoglobin and monitor body health.

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