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Low-Cost Interrogation System for Long-Period Fiber Gratings Applied to Remote Sensing

1
INESC TEC—Institute for Systems and Computer Engineering, Technology and Science, 4200-465 Porto, Portugal
2
Department of Physics and Astronomy of Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal
3
Department of Physics, School of Sciences and Technology, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
*
Authors to whom correspondence should be addressed.
Sensors 2019, 19(7), 1500; https://doi.org/10.3390/s19071500
Received: 5 March 2019 / Revised: 15 March 2019 / Accepted: 24 March 2019 / Published: 28 March 2019
(This article belongs to the Special Issue Optical Fiber Sensors 2018–2019)
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Abstract

We present a portable and low-cost system for interrogation of long-period fiber gratings (LPFGs) costing around a 30th of the price of a typical setup using an optical spectrum analyzer and a broadband light source. The unit is capable of performing real-time monitoring or as a stand-alone data-logger. The proposed technique uses three thermally modulated fiber-coupled laser diodes, sweeping a few nanometers around their central wavelength. The light signal is then modulated by the LPFG and its intensity is acquired by a single photo-detector. Through curve-fitting algorithms the sensor transmission spectrum is reconstructed. Testing and validation were accomplished by inducing variations in the spectral features of an LPFG through changes either in external air temperature from 22 to 425 °C or in refractive index (RI) of the surrounding medium from 1.3000 to 1.4240. A dynamic resolution between 3.5 and 1.9 °C was achieved, in temperatures from 125 to 325 °C. In RI measurements, maximum wavelength and optical power deviations of 2.75 nm and 2.86 dB, respectively, were obtained in the range from 1530 to 1570 nm. The worse RI resolution obtained was 3.47 × 10 3 . The interrogation platform was then applied in the detection of iron corrosion, expressing wavelength peak values within 1.12 nm from the real value in the region between 1530 and 1570 nm. View Full-Text
Keywords: long period fiber grating; interrogation system; corrosion sensing; remote sensing; optical fiber sensor long period fiber grating; interrogation system; corrosion sensing; remote sensing; optical fiber sensor
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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dos Santos, P.; Jorge, P.; de Almeida, J.M.; Coelho, L. Low-Cost Interrogation System for Long-Period Fiber Gratings Applied to Remote Sensing. Sensors 2019, 19, 1500.

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