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Fiber Optic Sensors and Applications Ⅱ
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Fiber Optic Sensors and Applications Ⅱ

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 12279

Special Issue Editors

Prof. Dr. Swee Chuan Tjin

E-Mail Website
Guest Editor
School of Electrical and Electronics Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Interests: fibre optic sensors; biomedical engineering and biophotonics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Lei Wei

E-Mail Website
Guest Editor
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore
Interests: fiber sensors; multifunctional fibers; fiber-based wearable electronics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue is focused on all aspects of the recent research and development related to fiber optic sensors. The recent advances in fiber-based sensing technologies have enabled both fundamental studies and a wide spectrum of applications. The goal of this Special Issue is to bring attention to the most recent results in the field of fiber optic sensors, including new mechanisms, materials, processes, and applications. Contributions on applications of novel or existing fiber optic sensors are also welcome, especially those highlighting the opportunities offered by the unique features in optical fibers or the advantages of fiber sensor configuration with respect to current technologies.

Relevant topics include, but are not limited to, the following:

  • Advanced fiber design and fabrication for sensing applications;
  • Fiber sensors for mechanical, chemical, environmental, biological, and medical applications;
  • Applications in industry, life sciences, oil and gas, civil engineering, materials, and defense;
  • Micro- and nanostructured fiber sensors;
  • Fiber lasers for sensing applications;
  • Distributed sensing;
  • Sensor integration and data fusion, network architectures, packaging, and long-term reliability;
  • Lab-on-fibers.
  • AI-enabled fiber optic sensing and data processing.

Prof. Dr. Swee Chuan Tjin
Prof. Dr. Lei Wei
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • fiber optic sensors
  • fabrication of fiber sensors
  • fiber lasers
  • multifunctional sensors
  • biophotonics
  • sensing systems
  • sensing signal and data processing

Published Papers (5 papers)

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Research

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11 pages, 3741 KiB  
Article
Fiber-Optic Temperature Sensor Using Cholesteric Liquid Crystals on the Optical Fiber Ferrules
by Soyeon Ahn, Gi Hyen Lee, Jun-Yong Lee, Youngseo Kim, Min Su Kim, Srinivas Pagidi, Byeong Kwon Choi, Ji Su Kim, Jong-Hyun Kim and Min Yong Jeon
Sensors 2022, 22(15), 5752; https://doi.org/10.3390/s22155752 - 01 Aug 2022
Cited by 3 | Viewed by 1649
Abstract
Cholesteric liquid crystals (CLCs) can be applied to various physical and chemical sensors because their alignment structures are changed by external stimuli. Here, we propose a CLC device fabricated by vertically forming the helical axis of the CLC between the cross-sections of two [...] Read more.
Cholesteric liquid crystals (CLCs) can be applied to various physical and chemical sensors because their alignment structures are changed by external stimuli. Here, we propose a CLC device fabricated by vertically forming the helical axis of the CLC between the cross-sections of two optical fiber ferrules. An optical fiber temperature sensor was successfully implemented using the proposed optical fiber ferrule-based CLC device. A wideband wavelength-swept laser with a center wavelength of 1073 nm and scanning range of 220 nm was used as a light source to measure the variations in the reflection spectrum band according to the temperature change in the CLC cell. The wavelength variation of the reflection spectrum band according to the temperature applied to the CLC cell was reversible and changed linearly with a change in the temperature, and the long-wavelength edge variation rate according to the temperature change was −5.0 nm/°C. Additionally, as the temperature applied to the CLC cell increased, the reflection spectrum bandwidth gradually decreased; the reflection spectrum bandwidth varied at a rate of −1.89 nm/°C. The variations in the refractive indices with temperature were calculated from the band wavelengths of the reflection spectrum. The pitch at each temperature was calculated based on the refractive indices and it gradually decreased as the temperature increased. Full article
(This article belongs to the Special Issue Fiber Optic Sensors and Applications Ⅱ)
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20 pages, 7023 KiB  
Article
Comparative In Situ Study of Dynamic Load Generated by Gravel Piles Measured by a Fiber-Optic Interferometer
by Martin Stolárik, Stanislav Kepák, Miroslav Pinka, Jakub Čubík and Jan Nedoma
Sensors 2022, 22(15), 5579; https://doi.org/10.3390/s22155579 - 26 Jul 2022
Cited by 1 | Viewed by 1105
Abstract
Currently, all the technology used for seismic monitoring is based on sensors in the electrical domain. There are, however, other physical principles that may enable and fully replace existing devices in the future. This paper introduces one of these approaches, namely the field [...] Read more.
Currently, all the technology used for seismic monitoring is based on sensors in the electrical domain. There are, however, other physical principles that may enable and fully replace existing devices in the future. This paper introduces one of these approaches, namely the field of fiber optics, which has great potential to be fully applied in the field of vibration measurement. The proposed solution uses a Michelson fiber-optic interferometer designed without polarization fading and with an operationally passive demodulation technique using three mutually phase-shifted optical outputs. Standard instrumentation commonly used in the field of seismic monitoring in geotechnical engineering was used as a reference. Comparative measurements were carried out during the implementation of gravel piles, which represents a significant source of vibration. For the correlation of the data obtained, the linear dependence previously verified in laboratory measurements was used. The presented results show that the correlation is also highly favorable (correlation coefficient in excess of 0.9) from the values measured in situ, with an average deviation for the oscillation velocity amplitude of the optical sensor not exceeding 0.0052. Full article
(This article belongs to the Special Issue Fiber Optic Sensors and Applications Ⅱ)
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10 pages, 2726 KiB  
Communication
Output Stabilization of Wavelength-Swept Laser Based on Closed-Loop Control of Fabry–Pérot Tunable Wavelength Filter for Fiber-Optic Sensors
by Byeong Kwon Choi, Soyeon Ahn, Ji Su Kim, Srinivas Pagidi and Min Yong Jeon
Sensors 2022, 22(12), 4337; https://doi.org/10.3390/s22124337 - 08 Jun 2022
Cited by 6 | Viewed by 1633
Abstract
The output of a wavelength-swept laser (WSL) based on a fiber Fabry–Pérot tunable filter (FFP-TF) tends to shift the peak wavelength due to external temperature or heat generated by the FFP-TF itself. Therefore, when measuring the output of WSL for a long time, [...] Read more.
The output of a wavelength-swept laser (WSL) based on a fiber Fabry–Pérot tunable filter (FFP-TF) tends to shift the peak wavelength due to external temperature or heat generated by the FFP-TF itself. Therefore, when measuring the output of WSL for a long time, it is very difficult to accurately measure a signal in the temporal domain corresponding to a specific wavelength of the output of the WSL. If the wavelength variation of the WSL output can be predicted through the peak time information of the forward scan or the backward scan from the WSL, the variation of the peak wavelength can be compensated for by adjusting the offset voltage applied to the FFP-TF. This study presents a successful stabilization method for peak wavelength variation in WSLs by adjusting the offset voltage of the FFP-TF with closed-loop control. The closed-loop control is implemented by measuring the deviation in the WSL peak position in the temporal domain using the trigger signal of the function generator. The feedback repetition rate for WSL stabilization was approximately 0.2 s, confirming that the WSL output and the peak position for the fiber Bragg grating (FBG) reflection spectrum were kept constant within ±7 μs at the maximum when the stabilization loop was applied. The standard deviations of WSL output and reflection peak positions were 1.52 μs and 1.59 μs, respectively. The temporal and spectral domains have a linear relationship; the ±7 μs maximum variation of the peak position corresponded to ±0.035 nm of the maximum wavelength variation in the spectral domain. The proposed WSL system can be used as a light source for temperature or strain-dependent sensors as it compensates for the WSL wavelength variation in applications that do not require a fast scanning rate. Full article
(This article belongs to the Special Issue Fiber Optic Sensors and Applications Ⅱ)
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13 pages, 5047 KiB  
Article
Highly Modulated In-Fiber Mach–Zehnder Interferometer Based on an Ultracompact Leaky-Guided Liquid Core
by Cheng-Ling Lee, Wei-Rong Zhuo and Tai-Kai Liu
Sensors 2022, 22(3), 808; https://doi.org/10.3390/s22030808 - 21 Jan 2022
Viewed by 1628
Abstract
We proposed a novel sensor based on an ultracompact leaky-guided liquid core fiber Mach–Zehnder interferometer (LLCFMZI) for high modulation of an interference spectrum. The sensor structure is based on a micro-sized hollow-core fiber (HCF) splicing a tilt end face single-mode fiber (SMF) to [...] Read more.
We proposed a novel sensor based on an ultracompact leaky-guided liquid core fiber Mach–Zehnder interferometer (LLCFMZI) for high modulation of an interference spectrum. The sensor structure is based on a micro-sized hollow-core fiber (HCF) splicing a tilt end face single-mode fiber (SMF) to create a miniature oblique gap for the effective access of different liquids. The liquid core with a relatively lower refractive index (RI) than the cladding can achieve a leaky-mode optical waveguide (LMOW) mechanism, and its volume is only approximately 7.85 pL. In addition, the utilized micro-length HCF can reduce the energy loss of core in the LMOW to obtain an acceptable extinction ratio (>30 dB) with high temperature (T) sensitivity in the interference spectra. Experimental results show that the interference spectra can be highly modulated within the wide measurement range of 1250–1650 nm with a steadily linear response for thermal effect. The measured temperature sensitivities (T-sensitivities) of various liquids of DI water, ethanol, and Cargille-liquid (nD = 1.305) are 0.8869, 4.4754, and 4.8229 nm/°C, and the corresponding measured thermal optics coefficient (TOC) are −4.16 × 10−5, −2.11 × 10−4, and −3.6 × 10−4 °C−1, respectively. Measurement results demonstrate that the used liquids with a higher TOC can obtain better T-sensitivity modulation. The highest experimental sensitivity of the liquid-core filled with Cargille-liquid (nD = 1.40) is up to +13.87 nm/°C with a corresponding TOC of −4.07 × 10−4 °C−1. Furthermore, the experimental and theoretical values are in good agreement according to FSR the measuring scheme that investigates the effectiveness of the proposed LLCFMZI. Full article
(This article belongs to the Special Issue Fiber Optic Sensors and Applications Ⅱ)
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Review

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23 pages, 32165 KiB  
Review
Recent Advances in Optical Fiber Enabled Radiation Sensors
by Jing Zhang, Yudiao Xiang, Chen Wang, Yunkang Chen, Swee Chuan Tjin and Lei Wei
Sensors 2022, 22(3), 1126; https://doi.org/10.3390/s22031126 - 01 Feb 2022
Cited by 20 | Viewed by 5175
Abstract
Optical fibers are being widely utilized as radiation sensors and dosimeters. Benefiting from the rapidly growing optical fiber manufacturing and material engineering, advanced optical fibers have evolved significantly by using functional structures and materials, promoting their detection accuracy and usage scenarios as radiation [...] Read more.
Optical fibers are being widely utilized as radiation sensors and dosimeters. Benefiting from the rapidly growing optical fiber manufacturing and material engineering, advanced optical fibers have evolved significantly by using functional structures and materials, promoting their detection accuracy and usage scenarios as radiation sensors. This paper summarizes the current development of optical fiber-based radiation sensors. The sensing principles of both extrinsic and intrinsic optical fiber radiation sensors, including radiation-induced attenuation (RIA), radiation-induced luminescence (RIL), and fiber grating wavelength shifting (RI-GWS), were analyzed. The relevant advanced fiber materials and structures, including silica glass, doped silica glasses, polymers, fluorescent and scintillator materials, were also categorized and summarized based on their characteristics. The fabrication methods of intrinsic all-fiber radiation sensors were introduced, as well. Moreover, the applicable scenarios from medical dosimetry to industrial environmental monitoring were discussed. In the end, both challenges and perspectives of fiber-based radiation sensors and fiber-shaped radiation dosimeters were presented. Full article
(This article belongs to the Special Issue Fiber Optic Sensors and Applications Ⅱ)
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