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. 2016 Dec 13;16(12):2119.
doi: 10.3390/s16122119.

Refractive Index Sensing with D-Shaped Plastic Optical Fibers for Chemical and Biochemical Applications

Filipa Sequeira  1   2 , Daniel Duarte  3 , Lúcia Bilro  4   5 , Alisa Rudnitskaya  6   7 , Maria Pesavento  8 , Luigi Zeni  9 , Nunzio Cennamo  10
Affiliations

Refractive Index Sensing with D-Shaped Plastic Optical Fibers for Chemical and Biochemical Applications

Filipa Sequeira et al. Sensors (Basel). .

Abstract

We report the optimization of the length of a D-shaped plastic optical fiber (POF) sensor for refractive index (RI) sensing from a numerical and experimental point of view. The sensing principle is based on total internal reflection (TIR). POFs with 1 mm in diameter were embedded in grooves, realized in planar supports with different lengths, and polished to remove the cladding and part of the core. All D-shaped POF sensors were tested using aqueous medium with different refractive indices (from 1.332 to 1.471) through intensity-based configuration. Results showed two different responses. Considering the refractive index (RI) range (1.33-1.39), the sensitivity and the resolution of the sensor were strongly dependent on the sensing region length. The highest sensitivity (resolution of 6.48 × 10-3 refractive index units, RIU) was obtained with 6 cm sensing length. In the RI range (1.41-1.47), the length of the sensing region was not a critical aspect to obtain the best resolution. These results enable the application of this optical platform for chemical and biochemical evanescent field sensing. The sensor production procedure is very simple, fast, and low-cost.

Keywords: chemical and biochemical sensing; optical fiber sensors; plastic optical fiber (POF); refractive index sensors; remote sensing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
D-shaped sensors: (a) lengths of the sensing region ranging from 1 cm (Sensor 1) to 6 cm (Sensor 6); (b) Close-up of Sensor 1, with sensing region of 1 cm length.
Figure 2
Figure 2
Image of a D-shaped fiber, where d is the fiber diameter, r the radius, h the depth, and w the half width of the sensing region.
Figure 3
Figure 3
SEM images of the D-shaped sensors: (a) Sensor 2; (b) Sensor 5.
Figure 4
Figure 4
(a) Outline of the experimental setup; (b) LED spectrum.
Figure 5
Figure 5
Normalized smooth signal vs. refractive index (RI) for all D-shaped sensors, RI range 1.33–1.47.
Figure 6
Figure 6
Normalized smooth signal vs. refractive index: (a) RI: 1.33–1.39, linear fitting; (b) RI: 1.41–1.47, exponential fitting.
Figure 7
Figure 7
RI: 1.33–1.39: (a) Sensitivity and (b) resolution of the D-shaped sensors vs. length of the sensing region. For the D-shaped sensor with 1 cm length (Sensor 1), the resolution obtained is for the refractive index range 1.33–1.37 RIU.
Figure 8
Figure 8
RI: 1.41–1.47: (a) Sensitivity and (b) resolution of the D-shaped sensors vs. length of the sensing region.
Figure 9
Figure 9
Experimental and simulation results: normalized smooth signal vs. refractive index for all D-shaped sensors in the RI range (1.33–1.39).
See this image and copyright information in PMC

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