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Special Issue "Optical Fiber Sensors 2016"

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

Deadline for manuscript submissions: closed (30 September 2016).

Special Issue Editors

Guest Editor
Prof. Dr. Manuel Lopez-Amo

Department of Electrical and Electronic Engineering, Universidad Publica de Navarra, Pamplona 31006 Spain
Website | E-Mail
Interests: optical fiber sensors, optical fiber lasers, optical fiber networks
Guest Editor
Prof. Dr. Jose Miguel Lopez-Higuera

Photonic Engineering Group of: 1 Universidad de Cantabria, 2 CIBER-BBN and 3 IDIVAL, Santander, Cantabria, Spain
Website | E-Mail
Interests: sensing using light; photonic/optical/fiber optic sensors
Guest Editor
Prof. Dr. Jose Luis Santos

Departamento de Física e Astronomia, Universidade do Porto, Rua Campo Alegre 687 Porto 4169-007 Portugal
Website | E-Mail
Interests: optical fiber sensors; optical devices

Special Issue Information

Dear Colleagues,

This special issue of the journal Sensors entitled:”Optical fiber sensors” will focus on all aspects of research and development related to this field. The scope covers all topics associated with sensing supported by guided optics platforms with emphasis on optical fibers, addressing subjects such as sensing transducers, sensing systems and applications in industrial, life sciences, medical, oil and gas, civil engineering, materials and defense, among others. Manuscripts are also welcome in domains such as self-diagnosis and recalibration, sensor integration and data fusion, network architectures, packaging, system robustness and long-term reliability.

Relevant topics include, but are not limited to:

  • Physical, mechanical, and electromagnetic sensors
  • Chemical, environmental, biological and medical sensors and bio photonics
  • Interferometric and polarimetric sensors including gyroscopes
  • Micro- and nano-structured fiber sensors including the photonic crystal fibers and gratings sensors
  • Multiplexing and sensor networking
  • Distributed sensing
  • Smart structures and sensors including the SHM systems
  • Sensor application, field tests and standardization
  • New fibers, devices and subsystems for photonic sensing including the ones for security and defense
  • New concepts for photonic sensing

Prof. Dr. Manuel Lopez-Amo
Prof. Dr. Jose Miguel Lopez-Higuera
Prof. Dr. Jose Luis Santos
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 papers will be 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 1800 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.

Published Papers (22 papers)

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Research

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Open AccessArticle
A Fiber-Optic Interferometric Tri-Component Geophone for Ocean Floor Seismic Monitoring
Sensors 2017, 17(1), 47; https://doi.org/10.3390/s17010047
Received: 22 October 2016 / Revised: 7 December 2016 / Accepted: 23 December 2016 / Published: 28 December 2016
Cited by 4 | PDF Full-text (3318 KB) | HTML Full-text | XML Full-text
Abstract
For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested. A compliant cylinder-based sensor head is analyzed with finite element method and tested. The operation frequency ranges from 2 [...] Read more.
For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested. A compliant cylinder-based sensor head is analyzed with finite element method and tested. The operation frequency ranges from 2 Hz to 150 Hz for acceleration detection, employing a phase generated carrier demodulation scheme, with a responsivity above 50 dB re rad/g for the whole frequency range. The transverse suppression ratio is about 30 dB. The system noise at low frequency originated mainly from the 1/f fluctuation, with an average system noise level −123.55 dB re rad / Hz ranging from 0 Hz to 500 Hz. The minimum detectable acceleration is about 2 ng / Hz , and the dynamic range is above 116 dB. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Tapered Polymer Fiber Sensors for Reinforced Concrete Beam Vibration Detection
Sensors 2016, 16(12), 2149; https://doi.org/10.3390/s16122149
Received: 6 September 2016 / Revised: 22 November 2016 / Accepted: 23 November 2016 / Published: 16 December 2016
Cited by 1 | PDF Full-text (4749 KB) | HTML Full-text | XML Full-text
Abstract
In this study, tapered polymer fiber sensors (TPFSs) have been employed to detect the vibration of a reinforced concrete beam (RC beam). The sensing principle was based on transmission modes theory. The natural frequency of an RC beam was theoretically analyzed. Experiments were [...] Read more.
In this study, tapered polymer fiber sensors (TPFSs) have been employed to detect the vibration of a reinforced concrete beam (RC beam). The sensing principle was based on transmission modes theory. The natural frequency of an RC beam was theoretically analyzed. Experiments were carried out with sensors mounted on the surface or embedded in the RC beam. Vibration detection results agreed well with Kistler accelerometers. The experimental results found that both the accelerometer and TPFS detected the natural frequency function of a vibrated RC beam well. The mode shapes of the RC beam were also found by using the TPFSs. The proposed vibration detection method provides a cost-comparable solution for a structural health monitoring (SHM) system in civil engineering. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs
Sensors 2016, 16(12), 2007; https://doi.org/10.3390/s16122007
Received: 30 September 2016 / Revised: 21 November 2016 / Accepted: 23 November 2016 / Published: 26 November 2016
Cited by 10 | PDF Full-text (3831 KB) | HTML Full-text | XML Full-text
Abstract
Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized [...] Read more.
Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Probabilistic Model Updating for Sizing of Hole-Edge Crack Using Fiber Bragg Grating Sensors and the High-Order Extended Finite Element Method
Sensors 2016, 16(11), 1956; https://doi.org/10.3390/s16111956
Received: 8 October 2016 / Revised: 16 November 2016 / Accepted: 17 November 2016 / Published: 21 November 2016
Cited by 12 | PDF Full-text (5694 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a novel framework for probabilistic crack size quantification using fiber Bragg grating (FBG) sensors. The key idea is to use a high-order extended finite element method (XFEM) together with a transfer (T)-matrix method to analyze the reflection intensity spectra of [...] Read more.
This paper presents a novel framework for probabilistic crack size quantification using fiber Bragg grating (FBG) sensors. The key idea is to use a high-order extended finite element method (XFEM) together with a transfer (T)-matrix method to analyze the reflection intensity spectra of FBG sensors, for various crack sizes. Compared with the standard FEM, the XFEM offers two superior capabilities: (i) a more accurate representation of fields in the vicinity of the crack tip singularity and (ii) alleviation of the need for costly re-meshing as the crack size changes. Apart from the classical four-term asymptotic enrichment functions in XFEM, we also propose to incorporate higher-order functions, aiming to further improve the accuracy of strain fields upon which the reflection intensity spectra are based. The wavelength of the reflection intensity spectra is extracted as a damage sensitive quantity, and a baseline model with five parameters is established to quantify its correlation with the crack size. In order to test the feasibility of the predictive model, we design FBG sensor-based experiments to detect fatigue crack growth in structures. Furthermore, a Bayesian method is proposed to update the parameters of the baseline model using only a few available experimental data points (wavelength versus crack size) measured by one of the FBG sensors and an optical microscope, respectively. Given the remaining data points of wavelengths, even measured by FBG sensors at different positions, the updated model is shown to give crack size predictions that match well with the experimental observations. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Tip-Clearance Measurement in the First Stage of the Compressor of an Aircraft Engine
Sensors 2016, 16(11), 1897; https://doi.org/10.3390/s16111897
Received: 30 September 2016 / Revised: 2 November 2016 / Accepted: 4 November 2016 / Published: 11 November 2016
Cited by 7 | PDF Full-text (6810 KB) | HTML Full-text | XML Full-text
Abstract
In this article, we report the design of a reflective intensity-modulated optical fiber sensor for blade tip-clearance measurement, and the experimental results for the first stage of a compressor of an aircraft engine operating in real conditions. The tests were performed in a [...] Read more.
In this article, we report the design of a reflective intensity-modulated optical fiber sensor for blade tip-clearance measurement, and the experimental results for the first stage of a compressor of an aircraft engine operating in real conditions. The tests were performed in a ground test cell, where the engine completed four cycles from idling state to takeoff and back to idling state. During these tests, the rotational speed of the compressor ranged between 7000 and 15,600 rpm. The main component of the sensor is a tetrafurcated bundle of optical fibers, with which the resulting precision of the experimental measurements was 12 µm for a measurement range from 2 to 4 mm. To get this precision the effect of temperature on the optoelectronic components of the sensor was compensated by calibrating the sensor in a climate chamber. A custom-designed MATLAB program was employed to simulate the behavior of the sensor prior to its manufacture. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Strain Measurement in Aluminium Alloy during the Solidification Process Using Embedded Fibre Bragg Gratings
Sensors 2016, 16(11), 1853; https://doi.org/10.3390/s16111853
Received: 28 September 2016 / Revised: 24 October 2016 / Accepted: 25 October 2016 / Published: 4 November 2016
Cited by 3 | PDF Full-text (3181 KB) | HTML Full-text | XML Full-text
Abstract
In recent years, the observation of the behaviour of components during the production process and over their life cycle is of increasing importance. Structural health monitoring, for example of carbon composites, is state-of-the-art research. The usage of Fibre Bragg Gratings (FBGs) in this [...] Read more.
In recent years, the observation of the behaviour of components during the production process and over their life cycle is of increasing importance. Structural health monitoring, for example of carbon composites, is state-of-the-art research. The usage of Fibre Bragg Gratings (FBGs) in this field is of major advantage. Another possible area of application is in foundries. The internal state of melts during the solidification process is of particular interest. By using embedded FBGs, temperature and stress can be monitored during the process. In this work, FBGs were embedded in aluminium alloys in order to observe the occurring strain. Two different FBG positions were chosen in the mould in order to compare its dependence. It was shown that FBGs can withstand the solidification process, although a compression in the range of one percent was measured, which is in agreement with the literature value. Furthermore, different lengths of the gratings were applied, and it was shown that shorter gratings result in more accurate measurements. The obtained results prove that FBGs are applicable as sensors for temperatures up to 740 °C. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Compensation of Verdet Constant Temperature Dependence by Crystal Core Temperature Measurement
Sensors 2016, 16(10), 1627; https://doi.org/10.3390/s16101627
Received: 23 August 2016 / Revised: 26 September 2016 / Accepted: 26 September 2016 / Published: 30 September 2016
Cited by 1 | PDF Full-text (1037 KB) | HTML Full-text | XML Full-text
Abstract
Compensation of the temperature dependence of the Verdet constant in a polarimetric extrinsic Faraday sensor is of major importance for applying the magneto-optical effect to AC current measurements and magnetic field sensing. This paper presents a method for compensating the temperature effect on [...] Read more.
Compensation of the temperature dependence of the Verdet constant in a polarimetric extrinsic Faraday sensor is of major importance for applying the magneto-optical effect to AC current measurements and magnetic field sensing. This paper presents a method for compensating the temperature effect on the Faraday rotation in a Bi12GeO20 crystal by sensing its optical activity effect on the polarization of a light beam. The method measures the temperature of the same volume of crystal that effects the beam polarization in a magnetic field or current sensing process. This eliminates the effect of temperature difference found in other indirect temperature compensation methods, thus allowing more accurate temperature compensation for the temperature dependence of the Verdet constant. The method does not require additional changes to an existing Δ/Σ configuration and is thus applicable for improving the performance of existing sensing devices. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
A Differential Reflective Intensity Optical Fiber Angular Displacement Sensor
Sensors 2016, 16(9), 1508; https://doi.org/10.3390/s16091508
Received: 14 July 2016 / Revised: 6 September 2016 / Accepted: 8 September 2016 / Published: 16 September 2016
Cited by 7 | PDF Full-text (5824 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel differential reflective intensity optical fiber angular displacement sensor was proposed. This sensor can directly measure the angular and axial linear displacement of a flat surface. The structure of the sensor probe is simple and its basic principle was [...] Read more.
In this paper, a novel differential reflective intensity optical fiber angular displacement sensor was proposed. This sensor can directly measure the angular and axial linear displacement of a flat surface. The structure of the sensor probe is simple and its basic principle was first analyzed according to the intensity modulation mechanisms. Secondly, in order to trim the dark output voltage to zero, the photoelectric conversion circuit was developed to adjust the signals. Then, the sensor model including the photoelectric conversion circuit has been established, and the influence of design parameters on the sensor output characteristic has been simulated. Finally, the design parameters of the sensor structure were obtained based on the simulation results; and an experimental test system was built for the sensor calibration. Experimental results show that the linear angular range and the sensitivity of the sensor were 74.4 and 0.051 V/°, respectively. Its change rules confirm the operating principle of the sensor well. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Research on the Error Characteristics of a 110 kV Optical Voltage Transformer under Three Conditions: In the Laboratory, Off-Line in the Field and During On-Line Operation
Sensors 2016, 16(8), 1303; https://doi.org/10.3390/s16081303
Received: 12 June 2016 / Revised: 8 August 2016 / Accepted: 9 August 2016 / Published: 16 August 2016
Cited by 2 | PDF Full-text (4509 KB) | HTML Full-text | XML Full-text
Abstract
Optical voltage transformers (OVTs) have been applied in power systems. When performing accuracy performance tests of OVTs large differences exist between the electromagnetic environment and the temperature variation in the laboratory and on-site. Therefore, OVTs may display different error characteristics under different conditions. [...] Read more.
Optical voltage transformers (OVTs) have been applied in power systems. When performing accuracy performance tests of OVTs large differences exist between the electromagnetic environment and the temperature variation in the laboratory and on-site. Therefore, OVTs may display different error characteristics under different conditions. In this paper, OVT prototypes with typical structures were selected to be tested for the error characteristics with the same testing equipment and testing method. The basic accuracy, the additional error caused by temperature and the adjacent phase in the laboratory, the accuracy in the field off-line, and the real-time monitoring error during on-line operation were tested. The error characteristics under the three conditions—laboratory, in the field off-line and during on-site operation—were compared and analyzed. The results showed that the effect of the transportation process, electromagnetic environment and the adjacent phase on the accuracy of OVTs could be ignored for level 0.2, but the error characteristics of OVTs are dependent on the environmental temperature and are sensitive to the temperature gradient. The temperature characteristics during on-line operation were significantly superior to those observed in the laboratory. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Model Study of the Influence of Ambient Temperature and Installation Types on Surface Temperature Measurement by Using a Fiber Bragg Grating Sensor
Sensors 2016, 16(7), 975; https://doi.org/10.3390/s16070975
Received: 2 April 2016 / Revised: 21 June 2016 / Accepted: 21 June 2016 / Published: 1 July 2016
Cited by 9 | PDF Full-text (4505 KB) | HTML Full-text | XML Full-text
Abstract
Surface temperature is an important parameter in clinical diagnosis, equipment state control, and environmental monitoring fields. The Fiber Bragg Grating (FBG) temperature sensor possesses numerous significant advantages over conventional electrical sensors, thus it is an ideal choice to achieve high-accuracy surface temperature measurements. [...] Read more.
Surface temperature is an important parameter in clinical diagnosis, equipment state control, and environmental monitoring fields. The Fiber Bragg Grating (FBG) temperature sensor possesses numerous significant advantages over conventional electrical sensors, thus it is an ideal choice to achieve high-accuracy surface temperature measurements. However, the effects of the ambient temperature and installation types on the measurement of surface temperature are often overlooked. A theoretical analysis is implemented and a thermal transfer model of a surface FBG sensor is established. The theoretical and simulated analysis shows that both substrate strain and the temperature difference between the fiber core and hot surface are the most important factors which affect measurement accuracy. A surface-type temperature standard setup is proposed to study the measurement error of the FBG temperature sensor. Experimental results show that there are two effects influencing measurement results. One is the “gradient effect”. This results in a positive linear error with increasing surface temperature. Another is the “substrate effect”. This results in a negative non-linear error with increasing surface temperature. The measurement error of the FBG sensor with single-ended fixation are determined by the gradient effect and is a linear error. It is not influenced by substrate expansion. Thus, it can be compensated easily. The measurement errors of the FBG sensor with double-ended fixation are determined by the two effects and the substrate effect is dominant. The measurement error change trend of the FBG sensor with fully-adhered fixation is similar to that with double-ended fixation. The adhesive layer can reduce the two effects and measurement error. The fully-adhered fixation has lower error, however, it is easily affected by substrate strain. Due to its linear error and strain-resistant characteristics, the single-ended fixation will play an important role in the FBG sensor encapsulation design field in the near future. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
A Fiber-Coupled Self-Mixing Laser Diode for the Measurement of Young’s Modulus
Sensors 2016, 16(6), 928; https://doi.org/10.3390/s16060928
Received: 11 April 2016 / Revised: 30 May 2016 / Accepted: 10 June 2016 / Published: 22 June 2016
Cited by 9 | PDF Full-text (2655 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the design of a fiber-coupled self-mixing laser diode (SMLD) for non-contact and non-destructive measurement of Young’s modulus. By the presented measuring system, the Young’s modulus of aluminum 6061 and brass are measured as 70.0 GPa and 116.7 GPa, respectively, showing [...] Read more.
This paper presents the design of a fiber-coupled self-mixing laser diode (SMLD) for non-contact and non-destructive measurement of Young’s modulus. By the presented measuring system, the Young’s modulus of aluminum 6061 and brass are measured as 70.0 GPa and 116.7 GPa, respectively, showing a good agreement within the standards in the literature and yielding a much smaller deviation and a higher repeatability compared with traditional tensile testing. Its fiber-coupled characteristics make the system quite easy to be installed in many application cases. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
A Core-Offset Mach Zehnder Interferometer Based on A Non-Zero Dispersion-Shifted Fiber and Its Torsion Sensing Application
Sensors 2016, 16(6), 856; https://doi.org/10.3390/s16060856
Received: 5 April 2016 / Revised: 6 June 2016 / Accepted: 7 June 2016 / Published: 10 June 2016
Cited by 21 | PDF Full-text (3873 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, an all-fiber Mach-Zehnder interferometer (MZI) based on a non-zero dispersion-shifted fiber (NZ-DSF) is presented. The MZI was implemented by core-offset fusion splicing one section of a NZ-DSF fiber between two pieces of single mode fibers (SMFs). Here, the NZ-DSF core [...] Read more.
In this paper, an all-fiber Mach-Zehnder interferometer (MZI) based on a non-zero dispersion-shifted fiber (NZ-DSF) is presented. The MZI was implemented by core-offset fusion splicing one section of a NZ-DSF fiber between two pieces of single mode fibers (SMFs). Here, the NZ-DSF core and cladding were used as the arms of the MZI, while the core-offset sections acted as optical fiber couplers. Thus, a MZI interference spectrum with a fringe contrast (FC) of about 20 dB was observed. Moreover, its response spectrum was experimentally characterized to the torsion parameter and a sensitivity of 0.070 nm/° was achieved. Finally, these MZIs can be implemented in a compact size and low cost. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
An Optical Fiber Lateral Displacement Measurement Method and Experiments Based on Reflective Grating Panel
Sensors 2016, 16(6), 808; https://doi.org/10.3390/s16060808
Received: 10 March 2016 / Revised: 25 May 2016 / Accepted: 30 May 2016 / Published: 2 June 2016
Cited by 2 | PDF Full-text (7670 KB) | HTML Full-text | XML Full-text
Abstract
An optical fiber sensing method based on a reflective grating panel is demonstrated for lateral displacement measurement. The reflective panel is a homemade grating with a periodic variation of its refractive index, which is used to modulate the reflected light intensity. The system [...] Read more.
An optical fiber sensing method based on a reflective grating panel is demonstrated for lateral displacement measurement. The reflective panel is a homemade grating with a periodic variation of its refractive index, which is used to modulate the reflected light intensity. The system structure and operation principle are illustrated in detail. The intensity calculation and simulation of the optical path are carried out to theoretically analyze the measurement performance. A distinctive fiber optic grating ruler with a special fiber optic measuring probe and reflective grating panel is set up. Experiments with different grating pitches are conducted, and long-distance measurements are executed to accomplish the functions of counting optical signals, subdivision, and discerning direction. Experimental results show that the proposed measurement method can be used to detect lateral displacement, especially for applications in working environments with high temperatures. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
An All-Fiber-Optic Combined System of Noncontact Photoacoustic Tomography and Optical Coherence Tomography
Sensors 2016, 16(5), 734; https://doi.org/10.3390/s16050734
Received: 20 March 2016 / Revised: 11 May 2016 / Accepted: 17 May 2016 / Published: 20 May 2016
Cited by 5 | PDF Full-text (2585 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We propose an all-fiber-based dual-modal imaging system that combines noncontact photoacoustic tomography (PAT) and optical coherence tomography (OCT). The PAT remotely measures photoacoustic (PA) signals with a 1550-nm laser on the surface of a sample by utilizing a fiber interferometer as an ultrasound [...] Read more.
We propose an all-fiber-based dual-modal imaging system that combines noncontact photoacoustic tomography (PAT) and optical coherence tomography (OCT). The PAT remotely measures photoacoustic (PA) signals with a 1550-nm laser on the surface of a sample by utilizing a fiber interferometer as an ultrasound detector. The fiber-based OCT, employing a swept-source laser centered at 1310 nm, shares the sample arm of the PAT system. The fiber-optic probe for the combined system was homemade with a lensed single-mode fiber (SMF) and a large-core multimode fiber (MMF). The compact and robust common probe is capable of obtaining both the PA and the OCT signals at the same position without any physical contact. Additionally, the MMF of the probe delivers the short pulses of a Nd:YAG laser to efficiently excite the PA signals. We experimentally demonstrate the feasibility of the proposed dual-modal system with a phantom made of a fishing line and a black polyethylene terephthalate fiber in a tissue mimicking solution. The all-fiber-optic system, capable of providing complementary information about absorption and scattering, has a promising potential in minimally invasive and endoscopic imaging. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Modeling of a Single-Notch Microfiber Coupler for High-Sensitivity and Low Detection-Limit Refractive Index Sensing
Sensors 2016, 16(5), 672; https://doi.org/10.3390/s16050672
Received: 28 February 2016 / Revised: 27 April 2016 / Accepted: 27 April 2016 / Published: 11 May 2016
Cited by 3 | PDF Full-text (3038 KB) | HTML Full-text | XML Full-text
Abstract
A highly sensitive refractive index sensor with low detection limit based on an asymmetric optical microfiber coupler is proposed. It is composed of a silica optical microfiber and an As2Se3 optical microfiber. Due to the asymmetry of the microfiber materials, [...] Read more.
A highly sensitive refractive index sensor with low detection limit based on an asymmetric optical microfiber coupler is proposed. It is composed of a silica optical microfiber and an As2Se3 optical microfiber. Due to the asymmetry of the microfiber materials, a single-notch transmission spectrum is demonstrated by the large refractive index difference between the two optical microfibers. Compared with the symmetric coupler, the bandwidth of the asymmetric structure is over one order of magnitude narrower than that of the former. Therefore, the asymmetric optical microfiber coupler based sensor can reach over one order of magnitude smaller detection limit, which is defined as the minimal detectable refractive index change caused by the surrounding analyte. With the advantage of large evanescent field, the results also show that a sensitivity of up to 3212 nm per refractive index unit with a bandwidth of 12 nm is achieved with the asymmetric optical microfiber coupler. Furthermore, a maximum sensitivity of 4549 nm per refractive index unit can be reached while the radii of the silica optical microfiber and As2Se3 optical microfiber are 0.5 μm and a 0.128 μm, respectively. This sensor component may have important potential for low detection-limit physical and biochemical sensing applications. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Intra-Tissue Pressure Measurement in Ex Vivo Liver Undergoing Laser Ablation with Fiber-Optic Fabry-Perot Probe
Sensors 2016, 16(4), 544; https://doi.org/10.3390/s16040544
Received: 16 March 2016 / Revised: 4 April 2016 / Accepted: 8 April 2016 / Published: 15 April 2016
Cited by 13 | PDF Full-text (1942 KB) | HTML Full-text | XML Full-text
Abstract
We report the first-ever intra-tissue pressure measurement performed during 1064 nm laser ablation (LA) of an ex vivo porcine liver. Pressure detection has been performed with a biocompatible, all-glass, temperature-insensitive Extrinsic Fabry-Perot Interferometry (EFPI) miniature probe; the proposed methodology mimics in-vivo treatment. Four [...] Read more.
We report the first-ever intra-tissue pressure measurement performed during 1064 nm laser ablation (LA) of an ex vivo porcine liver. Pressure detection has been performed with a biocompatible, all-glass, temperature-insensitive Extrinsic Fabry-Perot Interferometry (EFPI) miniature probe; the proposed methodology mimics in-vivo treatment. Four experiments have been performed, positioning the probe at different positions from the laser applicator tip (from 0.5 mm to 5 mm). Pressure levels increase during ablation time, and decrease with distance from applicator tip: the recorded peak parenchymal pressure levels range from 1.9 kPa to 71.6 kPa. Different pressure evolutions have been recorded, as pressure rises earlier in proximity of the tip. The present study is the first investigation of parenchymal pressure detection in liver undergoing LA: the successful detection of intra-tissue pressure may be a key asset for improving LA, as pressure levels have been correlated to scattered recurrences of tumors by different studies. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessArticle
Distributed Long-Gauge Optical Fiber Sensors Based Self-Sensing FRP Bar for Concrete Structure
Sensors 2016, 16(3), 286; https://doi.org/10.3390/s16030286
Received: 5 January 2016 / Revised: 15 February 2016 / Accepted: 19 February 2016 / Published: 25 February 2016
Cited by 12 | PDF Full-text (6091 KB) | HTML Full-text | XML Full-text
Abstract
Brillouin scattering-based distributed optical fiber (OF) sensing technique presents advantages for concrete structure monitoring. However, the existence of spatial resolution greatly decreases strain measurement accuracy especially around cracks. Meanwhile, the brittle feature of OF also hinders its further application. In this paper, the [...] Read more.
Brillouin scattering-based distributed optical fiber (OF) sensing technique presents advantages for concrete structure monitoring. However, the existence of spatial resolution greatly decreases strain measurement accuracy especially around cracks. Meanwhile, the brittle feature of OF also hinders its further application. In this paper, the distributed OF sensor was firstly proposed as long-gauge sensor to improve strain measurement accuracy. Then, a new type of self-sensing fiber reinforced polymer (FRP) bar was developed by embedding the packaged long-gauge OF sensors into FRP bar, followed by experimental studies on strain sensing, temperature sensing and basic mechanical properties. The results confirmed the superior strain sensing properties, namely satisfied accuracy, repeatability and linearity, as well as excellent mechanical performance. At the same time, the temperature sensing property was not influenced by the long-gauge package, making temperature compensation easy. Furthermore, the bonding performance between self-sensing FRP bar and concrete was investigated to study its influence on the sensing. Lastly, the sensing performance was further verified with static experiments of concrete beam reinforced with the proposed self-sensing FRP bar. Therefore, the self-sensing FRP bar has potential applications for long-term structural health monitoring (SHM) as embedded sensors as well as reinforcing materials for concrete structures. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Review

Jump to: Research

Open AccessFeature PaperReview
Fiber-Optic Sensors for Measurements of Torsion, Twist and Rotation: A Review
Sensors 2017, 17(3), 443; https://doi.org/10.3390/s17030443
Received: 31 December 2016 / Revised: 16 February 2017 / Accepted: 18 February 2017 / Published: 23 February 2017
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Abstract
Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been [...] Read more.
Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation.
Invited Paper Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessReview
Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications
Sensors 2016, 16(12), 2161; https://doi.org/10.3390/s16122161
Received: 9 October 2016 / Revised: 1 December 2016 / Accepted: 7 December 2016 / Published: 16 December 2016
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Abstract
Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of [...] Read more.
Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising. It is shown that optical rotational seismometer based on the ring-laser gyroscope concept is the best for seismological applications, whereas systems based on fiber-optic gyroscopes demonstrate parameters which are also required for engineering applications. Laboratory results of the Fibre-Optic System for Rotational Events & Phenomena Monitoring using a small 1-D shaking table modified to generate rotational excitations are presented. The harmonic and time-history tests demonstrate its usefulness for recording rotational motions with rates up to 0.25 rad/s. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessReview
Advanced Spatial-Division Multiplexed Measurement Systems Propositions—From Telecommunication to Sensing Applications: A Review
Sensors 2016, 16(9), 1387; https://doi.org/10.3390/s16091387
Received: 19 June 2016 / Revised: 23 August 2016 / Accepted: 24 August 2016 / Published: 30 August 2016
Cited by 20 | PDF Full-text (9797 KB) | HTML Full-text | XML Full-text
Abstract
The concepts of spatial-division multiplexing (SDM) technology were first proposed in the telecommunications industry as an indispensable solution to reduce the cost-per-bit of optical fiber transmission. Recently, such spatial channels and modes have been applied in optical sensing applications where the returned echo [...] Read more.
The concepts of spatial-division multiplexing (SDM) technology were first proposed in the telecommunications industry as an indispensable solution to reduce the cost-per-bit of optical fiber transmission. Recently, such spatial channels and modes have been applied in optical sensing applications where the returned echo is analyzed for the collection of essential environmental information. The key advantages of implementing SDM techniques in optical measurement systems include the multi-parameter discriminative capability and accuracy improvement. In this paper, to help readers without a telecommunication background better understand how the SDM-based sensing systems can be incorporated, the crucial components of SDM techniques, such as laser beam shaping, mode generation and conversion, multimode or multicore elements using special fibers and multiplexers are introduced, along with the recent developments in SDM amplifiers, opto-electronic sources and detection units of sensing systems. The examples of SDM-based sensing systems not only include Brillouin optical time-domain reflectometry or Brillouin optical time-domain analysis (BOTDR/BOTDA) using few-mode fibers (FMF) and the multicore fiber (MCF) based integrated fiber Bragg grating (FBG) sensors, but also involve the widely used components with their whole information used in the full multimode constructions, such as the whispering gallery modes for fiber profiling and chemical species measurements, the screw/twisted modes for examining water quality, as well as the optical beam shaping to improve cantilever deflection measurements. Besides, the various applications of SDM sensors, the cost efficiency issue, as well as how these complex mode multiplexing techniques might improve the standard fiber-optic sensor approaches using single-mode fibers (SMF) and photonic crystal fibers (PCF) have also been summarized. Finally, we conclude with a prospective outlook for the opportunities and challenges of SDM technologies in optical sensing industry. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessFeature PaperReview
Surface Plasmon Resonance-Based Fiber Optic Sensors Utilizing Molecular Imprinting
Sensors 2016, 16(9), 1381; https://doi.org/10.3390/s16091381
Received: 18 July 2016 / Revised: 17 August 2016 / Accepted: 25 August 2016 / Published: 29 August 2016
Cited by 23 | PDF Full-text (7216 KB) | HTML Full-text | XML Full-text
Abstract
Molecular imprinting is earning worldwide attention from researchers in the field of sensing and diagnostic applications, due to its properties of inevitable specific affinity for the template molecule. The fabrication of complementary template imprints allows this technique to achieve high selectivity for the [...] Read more.
Molecular imprinting is earning worldwide attention from researchers in the field of sensing and diagnostic applications, due to its properties of inevitable specific affinity for the template molecule. The fabrication of complementary template imprints allows this technique to achieve high selectivity for the analyte to be sensed. Sensors incorporating this technique along with surface plasmon or localized surface plasmon resonance (SPR/LSPR) provide highly sensitive real time detection with quick response times. Unfolding these techniques with optical fiber provide the additional advantages of miniaturized probes with ease of handling, online monitoring and remote sensing. In this review a summary of optical fiber sensors using the combined approaches of molecularly imprinted polymer (MIP) and the SPR/LSPR technique is discussed. An overview of the fundamentals of SPR/LSPR implementation on optical fiber is provided. The review also covers the molecular imprinting technology (MIT) with its elementary study, synthesis procedures and its applications for chemical and biological anlayte detection with different sensing methods. In conclusion, we explore the advantages, challenges and the future perspectives of developing highly sensitive and selective methods for the detection of analytes utilizing MIT with the SPR/LSPR phenomenon on optical fiber platforms. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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Open AccessReview
Fiber Optic Sensors for Temperature Monitoring during Thermal Treatments: An Overview
Sensors 2016, 16(7), 1144; https://doi.org/10.3390/s16071144
Received: 8 June 2016 / Revised: 15 July 2016 / Accepted: 18 July 2016 / Published: 22 July 2016
Cited by 58 | PDF Full-text (1763 KB) | HTML Full-text | XML Full-text | Correction
Abstract
During recent decades, minimally invasive thermal treatments (i.e., Radiofrequency ablation, Laser ablation, Microwave ablation, High Intensity Focused Ultrasound ablation, and Cryo-ablation) have gained widespread recognition in the field of tumor removal. These techniques induce a localized temperature increase or decrease to remove the [...] Read more.
During recent decades, minimally invasive thermal treatments (i.e., Radiofrequency ablation, Laser ablation, Microwave ablation, High Intensity Focused Ultrasound ablation, and Cryo-ablation) have gained widespread recognition in the field of tumor removal. These techniques induce a localized temperature increase or decrease to remove the tumor while the surrounding healthy tissue remains intact. An accurate measurement of tissue temperature may be particularly beneficial to improve treatment outcomes, because it can be used as a clear end-point to achieve complete tumor ablation and minimize recurrence. Among the several thermometric techniques used in this field, fiber optic sensors (FOSs) have several attractive features: high flexibility and small size of both sensor and cabling, allowing insertion of FOSs within deep-seated tissue; metrological characteristics, such as accuracy (better than 1 °C), sensitivity (e.g., 10 pm·°C−1 for Fiber Bragg Gratings), and frequency response (hundreds of kHz), are adequate for this application; immunity to electromagnetic interference allows the use of FOSs during Magnetic Resonance- or Computed Tomography-guided thermal procedures. In this review the current status of the most used FOSs for temperature monitoring during thermal procedure (e.g., fiber Bragg Grating sensors; fluoroptic sensors) is presented, with emphasis placed on their working principles and metrological characteristics. The essential physics of the common ablation techniques are included to explain the advantages of using FOSs during these procedures. Full article
(This article belongs to the Special Issue Optical Fiber Sensors 2016)
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