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Review
. 2020 Apr 28;20(9):2499.
doi: 10.3390/s20092499.

Fiber-Optic Skew Ray Sensors

George Y Chen  1 , Jinyu Wang  2 , David G Lancaster  1
Affiliations
Review

Fiber-Optic Skew Ray Sensors

George Y Chen et al. Sensors (Basel). .

Abstract

The evanescent fields along multimode fibers are usually relatively weak. To enhance the sensitivity of the resulting sensors, skew rays have been exploited for their larger number of total internal reflections and their more comprehensive spread over the fiber surface. The uniform distribution of light-matter interactions across the fiber surface facilitates high sensitivity through an increased interaction area, while mitigating the risk of laser-induced coating-material damage and photobleaching. Power-dependent measurements are less susceptible to temperature effects than interferometric techniques, and place loose requirements on the laser source. This review highlights the key developments in this area, while discussing the benefits, challenges as well as future development.

Keywords: evanescent field; multimode fiber; ray optics; sensor; skew ray.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Comparison of different excitation methods. Inset: propagation behavior for different ray types.
Figure 2
Figure 2
Comparison of different excitation methods. Inset: propagation behavior for different ray types.
Figure 3
Figure 3
Illustration of the experimental setup of a typical skew-ray-based optical sensor.
Figure 4
Figure 4
Emission of guided radiation from an on-axis fluorescer within a fluorescent optical fiber. Reproduced with permission [32]. Copyright 2015, SPIE.
Figure 5
Figure 5
(a) Normalized output angular power distribution for normalized input angles. (b) Normalized angular power distributions for various fiber lengths. Reproduced with permission [41]. Copyright 1975, The Optical Society.
Figure 6
Figure 6
Illustration of expected high-value regions of the detected parameter or sensitivity.
Figure 7
Figure 7
Illustration of the contribution to θϕ from the fiber-center offset and the input light angle.
Figure 8
Figure 8
Example variations of the sensing mechanism and measurands for skew-ray-based sensing.
Figure 9
Figure 9
Experimental curves of the normalized angle-resolved power for different polarization states [51]. Copyright 1996, Elsevier.
Figure 10
Figure 10
Sensor principle and evanescent wave field (fundamental mode) in an optical fiber. Reproduced with permission [62]. Copyright 2014, SPIE.
Figure 11
Figure 11
Experimental setup for the enhanced detection and quantification of Rhodamine B. Reproduced with permission [63]. Copyright Year, Publisher.
Figure 12
Figure 12
Attenuation (color depth) induced by 0.1 ng/mL concentration Rhodamine B relative to pure water as a function of launch angle and center offset. Reproduced with permission [64]. Copyright 2019, Elsevier.
See this image and copyright information in PMC

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