Abstract
We propose and numerically characterize the optical characteristics of a novel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor in the visible to near infrared (500-2000 nm) region for refractive index (RI) sensing. The finite element method (FEM) is used to design and study the influence of different geometric parameters on the sensing performance of the sensor. The chemically stable plasmonic material gold (Au) is used to produce excitation between the core and plasmonic mode. On a pure silica (SiO2) substrate, a rectangular structured core is used to facilitate the coupling strength between the core and the surface plasmon polariton (SPP) mode and thus improves the sensing performance. By tuning the geometric parameters, simulation results show a maximum wavelength sensitivity of 58000 nm/RIU (Refractive Index Unit) for the x polarization and 62000 nm/RIU for the y polarization for analyte refractive indices ranging from 1.33 to 1.43. Moreover, we characterize the amplitude sensitivity of the sensor that shows a maximum sensitivity of 1415 RIU-1 and 1293 RIU-1 for the x and y polarizations, respectively. To our knowledge, this is the highest sensitivity for an SPR in published literature, and facilitates future development of sensors for accurate and precise analyte measurement. The sensor also attains a maximum figure of merit (FOM) of 1140 and fine RI resolution of 1.6 × 10-6. Owing to strong coupling strength, high sensitivity, high FOM and improved sensing resolution, the proposed sensor is suited for real-time, inexpensive and accurate detection of biomedical and biological analytes, biomolecules, and organic chemicals.
Highlights
In the last few decades, surface plasmon resonance (SPR) sensing technology has reached a unique place because of its ability to achieve high sensitivity and reliability [1]
A sharp loss peak is obtained for a particular analyte of refractive index (RI) and an unknown analyte with different RI can be detected by observing the variation of loss peak and corresponding resonance wavelength
The sensor can achieve a maximum birefringence of 1.2 × 10−3 that facilitates the fiber to be operated in a dual polarized mode and improves the sensing performance
Summary
In the last few decades, surface plasmon resonance (SPR) sensing technology has reached a unique place because of its ability to achieve high sensitivity and reliability [1]. In the following year Huang et al proposed an indium tin-oxide based D-shaped sensor structure and obtained a maximum wavelength sensitivity of 6000 nm/RIU and a low amplitude sensitivity of 148 RIU−1 in the RI range of 1.28–1.34 [28]. The literature discussed above indicates that there is sufficient scope for new SPR sensor designs with improved sensing performance In this manuscript, utilizing an external sensing approach we propose a novel gold coated PCF-SPR sensor to operate in the visible to near-infrared region. For ease of fabrication and practical utilization of the sensor, the metal coating is applied to the outer surface of the fiber, with the plasmonic surface in direct contact with the analyte Various geometric parameters such as pitch distance, air hole diameter, core geometry, analyte channel thickness, metallic channel thickness and PML thickness are optimized for obtaining the desired performance
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