Refractive Index Sensing through Surface Plasmon Resonance in Light-Diffusing Fibers

Abstract

Abstract:In this paper, we show that light-diffusing fibers (LDF) can be efficiently used as host material for surface plasmon resonance (SPR)-based refractive index sensing. This novel platform does not require a chemical procedure to remove the cladding or enhance the evanescent field, which is expected to give better reproducibility of the sensing interface. The SPR sensor has been realized by first removing the cladding with a simple mechanical stripper, and then covering the unclad fiber surface with a thin gold film. The tests have been carried out using water-glycerin mixtures with refractive indices ranging from 1.332 to 1.394. The experimental results reveal a high sensitivity of the SPR wavelength to the outer medium's refractive index, with values ranging from 1500 to~4000 nm/RIU in the analyzed range. The results suggest that the proposed optical fiber sensor platform could be used in biochemical applications.

A Novel Approach to Realizing Low-Cost Plasmonic Optical Fiber Sensors: Light-Diffusing Fibers Covered by Thin Metal Films

“…In the following, we report the results of an SPR sensor fabricated by sputtering a thin silver film above the uncoated area of the same LDF used in Ref. [15]. Comparing the new results with those achieved for the gold-coated SPR sensor, we show that the silver-coated sensor is more sensitive to RI changes and exhibits a higher SNR than the gold-coated sensor.…”

“…For these multimode fibers, a ray-optic description of light transmission through a fiber can be used in order to compute the power transmitted through the LDF [15]. According to this model, each optical ray propagating over a sensing length L experiences an amount of optical loss, depending on the reflection coefficient at the core-cladding interface and the number of reflections.…”

“…When multimode optical fibers are illuminated by a lens with an NA greater than that of the fibers, in the fibers the power distribution among the different modes can be described with a Lambertian distribution [18]. However, in the case of light-diffusing fibers, a more accurate assumption is a perfectly scrambled angular distribution (P 0 (θ i ) = const in Equation (1)) [15], due to the scrambling of optical energy operated by exploiting the helical voids running along the core. Figure 3a,b show the experimental and numerical transmission spectra of the prepared sample.…”

“…However, SPR multimode sensors show a strong dependence of the SPR wavelength on the incidence angle of the incoming light [7,12]. We have recently demonstrated that a light-diffusing fiber (LDF), covered with a thin gold film, can be successfully employed as an SPR sensor platform [15]. Light-diffusing fibers have been designed with scattering centers in the core, leading to efficient light scattering through the sides of the optical fiber and along its length.…”

“…Light-diffusing fibers have been designed with scattering centers in the core, leading to efficient light scattering through the sides of the optical fiber and along its length. Thanks to random scattering, the SPR phenomenon of an LDF is essentially independent of the incidence angle of the excitation light [15].…”