Theoretical Investigation of a Highly Sensitive Refractive-Index Sensor Based on TM₀ Waveguide Mode Resonance Excited in an Asymmetric Metal-Cladding Dielectric Waveguide Structure.

Xiangxian Wang,Jiankai Zhu,Xiaoxiong Wu,Hua Yang,Yunping Qi,Zhiyuan Pang

doi:10.3390/s19051187

Abstract

This study proposes a highly sensitive refractive-index (RI) sensor based on a TM0 waveguide mode resonance excited in an asymmetric metal-cladding dielectric waveguide structure, where the analyte serves as the guiding layer. By scanning the wavelength at fixed angles of incidence, the reflection spectra of the sensor were obtained. The results showed that the resonance wavelength redshifted dramatically with increases in the analyte RI, which indicates that this approach can be used to sense both the resonance wavelength and the analyte RI. Based on this approach, we investigated the sensing properties, including the sensitivity and figure of merit, at fixed incident angles of 60° and 45°, at which the sensitivity of the sensor reached 7724.9 nm/RIU (refractive index units) and 1339 nm/RIU, respectively. Compared with surface plasmon resonance sensors, which are based on a similar structure, the proposed sensor can accept a more flexible range of incident angles and a wider sensing range of analyte RI. This approach thus has tremendous potential for use in numerous sensing domains, such as biochemical and medical analyses.

Highlights

Surface plasmon resonance (SPR) can generate a strong electromagnetic field enhancement on the surface of a metal structure, and is very sensitive to the surrounding environment
For refractive index sensors based on SPR, the resonance is excited mainly in two modes, the angular mode and the spectral mode [30,31]
Among the variety of structures used to excite SPR, two main structures are used in biochemical sensors that are based on prism- or grating-coupling structures [30,31]

Summary

Introduction

Surface plasmon resonance (SPR) can generate a strong electromagnetic field enhancement on the surface of a metal structure, and is very sensitive to the surrounding environment. In contrast to the prism-coupled SPR sensing method, we previously explored an improved RI sensing technique based on an asymmetric metal-cladding dielectric waveguide (AMDW) [34,38,39]. Based on this AMDW structure, we had considered a method to fabricate hierarchical, sub-wavelength, photonic structures with various periods and number of layers via high-order waveguide-mode interference [34]. It is noted that the detected analyte RI in the AMDW structure can even exceed that for prism-based methods This angular sensing method with a fixed incident wavelength requires mechanical rotation to continuously change incident angles, which is a complex operation with low efficiency. The results demonstrated the performance of the AMDW structure to sense the RI of the analytes

Sensor Design and Analysis

Conclusions

Results