Sensors

Research

1131 KiB

Open AccessArticle

Functionality Enhancement of Industrialized Optical Fiber Sensors and System Developed for Full-Scale Pavement Monitoring

by Huaping Wang, Wanqiu Liu, Jianping He, Xiaoying Xing, Dandan Cao, Xipeng Gao, Xiaowei Hao, Hongwei Cheng and Zhi Zhou

Sensors 2014, 14(5), 8829-8850; https://doi.org/10.3390/s140508829 - 19 May 2014

Cited by 34 | Viewed by 8758

Abstract

Pavements always play a predominant role in transportation. Health monitoring of pavements is becoming more and more significant, as frequently suffering from cracks, rutting, and slippage renders them prematurely out of service. Effective and reliable sensing elements are thus in high demand to [...] Read more.

Pavements always play a predominant role in transportation. Health monitoring of pavements is becoming more and more significant, as frequently suffering from cracks, rutting, and slippage renders them prematurely out of service. Effective and reliable sensing elements are thus in high demand to make prognosis on the mechanical properties and occurrence of damage to pavements. Therefore, in this paper, various types of functionality enhancement of industrialized optical fiber sensors for pavement monitoring are developed, with the corresponding operational principles clarified in theory and the performance double checked by basic experiments. Furthermore, a self-healing optical fiber sensing network system is adopted to accomplish full-scale monitoring of pavements. The application of optical fiber sensors assembly and self-healing network system in pavement has been carried out to validate the feasibility. It has been proved that the research in this article provides a valuable method and meaningful guidance for the integrity monitoring of civil structures, especially pavements. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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22467 KiB

Open AccessArticle

A Fiber Optic PD Sensor Using a Balanced Sagnac Interferometer and an EDFA-Based DOP Tunable Fiber Ring Laser

by Lutang Wang, Nian Fang, Chunxu Wu, Haijuan Qin and Zhaoming Huang

Sensors 2014, 14(5), 8398-8422; https://doi.org/10.3390/s140508398 - 12 May 2014

Cited by 35 | Viewed by 9669

Abstract

A novel fiber-optic acoustic sensor using an erbium-doped fiber amplifier (EDFA)-based fiber ring laser and a balanced Sagnac interferometer for acoustic sensing of the partial discharge (PD) in power transformers is proposed and demonstrated. As a technical background, an experimental investigation on how [...] Read more.

A novel fiber-optic acoustic sensor using an erbium-doped fiber amplifier (EDFA)-based fiber ring laser and a balanced Sagnac interferometer for acoustic sensing of the partial discharge (PD) in power transformers is proposed and demonstrated. As a technical background, an experimental investigation on how the variations of the fiber birefringence affect the sensor performances was carried out, and the results are discussed. The operation principles are described, and the relevant formulas are derived. The analytical results show that an EDFA-based fiber ring laser operating in chaotic mode can provide a degree of polarization (DOP) tunable light beam for effectively suppressing polarization fading noises. The balanced Sagnac interferometer can eliminate command intensity noises and enhance the signal-to-noise ratio (SNR). Furthermore, it inherently operates at the quadrature point of the response curve without any active stabilizations. Several experiments are conducted for evaluating the performances of the sensor system, as well as for investigating the ability of the detection of high-frequency acoustic emission signals. The experimental results demonstrate that the DOP of the laser beam can be continuously tuned from 0.2% to 100%, and the power fluctuation in the whole DOP tuning range is less than 0.05 dBm. A high-frequency response up to 300 kHz is reached, and the high sensing sensitivity for detections of weak corona discharges, as well as partial discharges also is verified. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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414 KiB

Open AccessArticle

Measurement of Cerenkov Radiation Induced by the Gamma-Rays of Co-60 Therapy Units Using Wavelength Shifting Fiber

by Kyoung Won Jang, Sang Hun Shin, Seon Geun Kim, Jae Seok Kim, Wook Jae Yoo, Young Hoon Ji and Bongsoo Lee

Sensors 2014, 14(4), 7013-7025; https://doi.org/10.3390/s140407013 - 21 Apr 2014

Cited by 17 | Viewed by 8761

Abstract

In this study, a wavelength shifting fiber that shifts ultra-violet and blue light to green light was employed as a sensor probe of a fiber-optic Cerenkov radiation sensor. In order to characterize Cerenkov radiation generated in the developed wavelength shifting fiber and a [...] Read more.

In this study, a wavelength shifting fiber that shifts ultra-violet and blue light to green light was employed as a sensor probe of a fiber-optic Cerenkov radiation sensor. In order to characterize Cerenkov radiation generated in the developed wavelength shifting fiber and a plastic optical fiber, spectra and intensities of Cerenkov radiation were measured with a spectrometer. The spectral peaks of light outputs from the wavelength shifting fiber and the plastic optical fiber were measured at wavelengths of 500 and 510 nm, respectively, and the intensity of transmitted light output of the wavelength shifting fiber was 22.2 times higher than that of the plastic optical fiber. Also, electron fluxes and total energy depositions of gamma-ray beams generated from a Co-60 therapy unit were calculated according to water depths using the Monte Carlo N-particle transport code. The relationship between the fluxes of electrons over the Cerenkov threshold energy and the energy depositions of gamma-ray beams from the Co-60 unit is a near-identity function. Finally, percentage depth doses for the gamma-ray beams were obtained using the fiber-optic Cerenkov radiation sensor, and the results were compared with those obtained by an ionization chamber. The average dose difference between the results of the fiber-optic Cerenkov radiation sensor and those of the ionization chamber was about 2.09%. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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194 KiB

Open AccessCommunication

Optimization of Dengue Immunoassay by Label-Free Interferometric Optical Detection Method

by María F. Laguna, Miguel Holgado, Francisco J. Sanza, Alvaro Lavín, Ana López and Rafael Casquel

Sensors 2014, 14(4), 6695-6700; https://doi.org/10.3390/s140406695 - 10 Apr 2014

Cited by 7 | Viewed by 6760

Abstract

In this communication we report a direct immunoassay for detecting dengue virus by means of a label-free interferometric optical detection method. We also demonstrate how we can optimize this sensing response by adding a blocking step able to significantly enhance the optical sensing [...] Read more.

In this communication we report a direct immunoassay for detecting dengue virus by means of a label-free interferometric optical detection method. We also demonstrate how we can optimize this sensing response by adding a blocking step able to significantly enhance the optical sensing response. The blocking reagent used for this optimization is a dry milk diluted in phosphate buffered saline. The recognition curve of dengue virus over the proposed surface sensor demonstrates the capacity of this method to be applied in Point of Care technology. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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1077 KiB

Open AccessArticle

Measurement of Entrance Surface Dose on an Anthropomorphic Thorax Phantom Using a Miniature Fiber-Optic Dosimeter

by Wook Jae Yoo, Sang Hun Shin, Dayeong Jeon, Seunghan Hong, Hyeok In Sim, Seon Geun Kim, Kyoung Won Jang, Seunghyun Cho, Won Sik Youn and Bongsoo Lee

Sensors 2014, 14(4), 6305-6316; https://doi.org/10.3390/s140406305 - 1 Apr 2014

Cited by 13 | Viewed by 7966

Abstract

A miniature fiber-optic dosimeter (FOD) system was fabricated using a plastic scintillating fiber, a plastic optical fiber, and a multi-pixel photon counter to measure real-time entrance surface dose (ESD) during radiation diagnosis. Under varying exposure parameters of a digital radiography (DR) system, we [...] Read more.

A miniature fiber-optic dosimeter (FOD) system was fabricated using a plastic scintillating fiber, a plastic optical fiber, and a multi-pixel photon counter to measure real-time entrance surface dose (ESD) during radiation diagnosis. Under varying exposure parameters of a digital radiography (DR) system, we measured the scintillating light related to the ESD using the sensing probe of the FOD, which was placed at the center of the beam field on an anthropomorphic thorax phantom. Also, we obtained DR images using a flat panel detector of the DR system to evaluate the effects of the dosimeter on image artifacts during posteroanterior (PA) chest radiography. From the experimental results, the scintillation output signals of the FOD were similar to the ESDs including backscatter simultaneously obtained using a semiconductor dosimeter. We demonstrated that the proposed miniature FOD can be used to measure real-time ESDs with minimization of DR image artifacts in the X-ray energy range of diagnostic radiology. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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499 KiB

Open AccessArticle

An Integrated Photoluminescence Sensing Platform Using a Single-Multi-Mode Fiber Coupler-Based Probe

by Feng Long, Anna Zhu and Hanchang Shi

Sensors 2014, 14(3), 5677-5686; https://doi.org/10.3390/s140305677 - 21 Mar 2014

Cited by 3 | Viewed by 6602

Abstract

We demonstrate an integrated fiber optic photoluminescence sensing platform using a novel single-multi-mode fiber coupler (SMFC)-based probe with high collection efficiency for fluorescence signals. The SMFC, prepared using fused biconical taper technology, not only transmits excitation light, but also collects and transmits fluorescence. [...] Read more.

We demonstrate an integrated fiber optic photoluminescence sensing platform using a novel single-multi-mode fiber coupler (SMFC)-based probe with high collection efficiency for fluorescence signals. The SMFC, prepared using fused biconical taper technology, not only transmits excitation light, but also collects and transmits fluorescence. The entire system does not use complex optical components and rarely requires optical alignment. The simple structure of the SMFC considerably improves the light transmission efficiency, signal-to-noise ratio, and sensitivity of the system. Theoretical and experimental results show that the proposed probe increases the collection efficiency by more than eight-fold compared with a bifurcated fiber probe. The performance of the proposed probe was experimentally evaluated by measuring the fluorescence spectra of well-known targets and a fresh Tall Fescue leaf. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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661 KiB

Open AccessArticle

Fibre Optic System for Monitoring Rotational Seismic Phenomena

by Anna Kurzych, Leszek R. Jaroszewicz, Zbigniew Krajewski, Krzysztof P. Teisseyre and Jerzy K. Kowalski

Sensors 2014, 14(3), 5459-5469; https://doi.org/10.3390/s140305459 - 19 Mar 2014

Cited by 21 | Viewed by 6553

Abstract

We outline the development and the application in a field test of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of the seismic-origin rotations of the ground. The main advantage of AFORS is its complete insensitivity [...] Read more.

We outline the development and the application in a field test of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of the seismic-origin rotations of the ground. The main advantage of AFORS is its complete insensitivity to linear motions, as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas the applied telemetric system based on the Internet allows for an AFORS remote control. The laboratory investigation of such two devices indicated that they keep an accuracy of no less than 5.1 × 10⁻⁹ to 5.5 × 10⁻⁸ rad/s in the detection frequency band from 0.83~106.15 Hz and protect linear changes of sensitivity in the above bandpass. Some experimental results of an AFORS-1 application for a continuous monitoring of the rotational events in the Książ (Poland) seismological observatory are also presented. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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1880 KiB

Open AccessArticle

Synthetic Spectrum Approach for Brillouin Optical Time-Domain Reflectometry

by Ken'ichi Nishiguchi, Che-Hsien Li, Artur Guzik and Kinzo Kishida

Sensors 2014, 14(3), 4731-4754; https://doi.org/10.3390/s140304731 - 7 Mar 2014

Cited by 32 | Viewed by 7788

Abstract

We propose a novel method to improve the spatial resolution of Brillouin optical time-domain reflectometry (BOTDR), referred to as synthetic BOTDR (S-BOTDR), and experimentally verify the resolution improvements. Due to the uncertainty relation between position and frequency, the spatial resolution of a conventional [...] Read more.

We propose a novel method to improve the spatial resolution of Brillouin optical time-domain reflectometry (BOTDR), referred to as synthetic BOTDR (S-BOTDR), and experimentally verify the resolution improvements. Due to the uncertainty relation between position and frequency, the spatial resolution of a conventional BOTDR system has been limited to about one meter. In S-BOTDR, a synthetic spectrum is obtained by combining four Brillouin spectrums measured with different composite pump lights and different composite low-pass filters. We mathematically show that the resolution limit, in principle, for conventional BOTDR can be surpassed by S-BOTDR and experimentally prove that S-BOTDR attained a 10-cm spatial resolution. To the best of our knowledge, this has never been achieved or reported. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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857 KiB

Open AccessArticle

Post-Impact Fatigue Damage Monitoring Using Fiber Bragg Grating Sensors

by Chow-Shing Shin, Shien-Kuei Liaw and Shi-Wei Yang

Sensors 2014, 14(3), 4144-4153; https://doi.org/10.3390/s140304144 - 3 Mar 2014

Cited by 16 | Viewed by 7208

Abstract

It has been shown that impact damage to composite materials can be revealed by embedded Fiber Bragg Gratings (FBG) as a broadening and splitting of the latter’s characteristic narrow peak reflected spectrum. The current work further subjected the impact damaged composite to cyclic [...] Read more.

It has been shown that impact damage to composite materials can be revealed by embedded Fiber Bragg Gratings (FBG) as a broadening and splitting of the latter’s characteristic narrow peak reflected spectrum. The current work further subjected the impact damaged composite to cyclic loading and found that the FBG spectrum gradually submerged into a rise of background intensity as internal damages progressed. By skipping the impact, directing the impact to positions away from the FBG and examining the extracted fibers, we concluded that the above change is not a result of deterioration/damage of the sensor. It is caused solely by the damages initiated in the composite by the impact and aggravated by fatigue loading. Evolution of the grating spectrum may therefore be used to monitor qualitatively the development of the incurred damages. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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541 KiB

Open AccessArticle

A Fiber Optic Ammonia Sensor Using a Universal pH Indicator

by Adolfo J. Rodríguez, Carlos R. Zamarreño, Ignacio R. Matías, Francisco. J. Arregui, Rene F. Domínguez Cruz and Daniel. A. May-Arrioja

Sensors 2014, 14(3), 4060-4073; https://doi.org/10.3390/s140304060 - 27 Feb 2014

Cited by 37 | Viewed by 10200

Abstract

A universal pH indicator is used to fabricate a fiber optic ammonia sensor. The advantage of this pH indicator is that it exhibits sensitivity to ammonia over a broad wavelength range. This provides a differential response, with a valley around 500 nm and [...] Read more.

A universal pH indicator is used to fabricate a fiber optic ammonia sensor. The advantage of this pH indicator is that it exhibits sensitivity to ammonia over a broad wavelength range. This provides a differential response, with a valley around 500 nm and a peak around 650 nm, which allows us to perform ratiometric measurements. The ratiometric measurements provide not only an enhanced signal, but can also eliminate any external disturbance due to humidity or temperature fluctuations. In addition, the indicator is embedded in a hydrophobic and gas permeable polyurethane film named Tecoflex^®. The film provides additional advantages to the sensor, such as operation in dry environments, efficient transport of the element to be measured to the sensitive area of the sensor, and prevent leakage or detachment of the indicator. The combination of the universal pH indicator and Tecoflex^® film provides a reliable and robust fiber optic ammonia sensor. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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4787 KiB

Open AccessArticle

Description of an Advantageous Optical Label-Free Biosensing Interferometric Read-Out Method to Measure Biological Species

by Miguel Holgado, Francisco J. Sanza, Ana López, Álvaro Lavín, Rafael Casquel and María F. Laguna

Sensors 2014, 14(2), 3675-3689; https://doi.org/10.3390/s140203675 - 21 Feb 2014

Cited by 23 | Viewed by 8076

Abstract

In this article we report a new, simple, and reliable optical read-out detection method able to assess Rotavirus present in human sera as well as in the viral pollution sources. It is based on the interference of two interferometers used as biophotonic transducers. [...] Read more.

In this article we report a new, simple, and reliable optical read-out detection method able to assess Rotavirus present in human sera as well as in the viral pollution sources. It is based on the interference of two interferometers used as biophotonic transducers. The method significantly improves the optical label-free biosensing response measuring both, the concentration of the AgR and its corresponding size. Two different immunoassays were carried out: Bovine Serum Albumin (BSA), and the recognition by its antibody (anti-BSA); and Rotavirus (AgR) and the recognition by its antibody (anti-AgR). In the cases studied, and using as model interferometer a simple Fabry-Perot transducer, we demonstrate a biosensing enhancement of two orders of magnitude in the Limit of Detection (LoD). In fact, this read-out optical method may have significant implications to enhance other optical label-free photonic transducers reported in the scientific literature. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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759 KiB

Open AccessArticle

Characterization of Scintillating X-ray Optical Fiber Sensors

by Dan Sporea, Laura Mihai, Ion Vâţă, Denis McCarthy, Sinead O'Keeffe and Elfed Lewis

Sensors 2014, 14(2), 3445-3457; https://doi.org/10.3390/s140203445 - 19 Feb 2014

Cited by 12 | Viewed by 7583

Abstract

The paper presents a set of tests carried out in order to evaluate the design characteristics and the operating performance of a set of six X-ray extrinsic optical fiber sensors. The extrinsic sensor we developed is intended to be used as a low [...] Read more.

The paper presents a set of tests carried out in order to evaluate the design characteristics and the operating performance of a set of six X-ray extrinsic optical fiber sensors. The extrinsic sensor we developed is intended to be used as a low energy X-ray detector for monitoring radiation levels in radiotherapy, industrial applications and for personnel dosimetry. The reproducibility of the manufacturing process and the characteristics of the sensors were assessed. The sensors dynamic range, linearity, sensitivity, and reproducibility are evaluated through radioluminescence measurements, X-ray fluorescence and X-ray imaging investigations. Their response to the operating conditions of the excitation source was estimated. The effect of the sensors design and implementation, on the collecting efficiency of the radioluminescence signal was measured. The study indicated that the sensors are efficient only in the first 5 mm of the tip, and that a reflective coating can improve their response. Additional tests were done to investigate the concentricity of the sensors tip against the core of the optical fiber guiding the optical signal. The influence of the active material concentration on the sensor response to X-ray was studied. The tests were carried out by measuring the radioluminescence signal with an optical fiber spectrometer and with a Multi-Pixel Photon Counter. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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Graphical abstract

342 KiB

Open AccessArticle

An Optical Fiber-Based Sensor Array for the Monitoring of Zinc and Copper Ions in Aqueous Environments

by Steven Kopitzke and Peter Geissinger

Sensors 2014, 14(2), 3077-3094; https://doi.org/10.3390/s140203077 - 17 Feb 2014

Cited by 15 | Viewed by 7124

Abstract

Copper and zinc are elements commonly used in industrial applications as aqueous solutions. Before the solutions can be discharged into civil or native waterways, waste treatment processes must be undertaken to ensure compliance with government guidelines restricting the concentration of ions discharged in [...] Read more.

Copper and zinc are elements commonly used in industrial applications as aqueous solutions. Before the solutions can be discharged into civil or native waterways, waste treatment processes must be undertaken to ensure compliance with government guidelines restricting the concentration of ions discharged in solution. While currently there are methods of analysis available to monitor these solutions, each method has disadvantages, be it high costs, inaccuracy, and/or being time-consuming. In this work, a new optical fiber-based platform capable of providing fast and accurate results when performing solution analysis for these metals is described. Fluorescent compounds that exhibit a high sensitivity and selectivity for either zinc or copper have been employed for fabricating the sensors. These sensors demonstrated sub-part-per-million detection limits, 30-second response times, and the ability to analyze samples with an average error of under 10%. The inclusion of a fluorescent compound as a reference material to compensate for fluctuations from pulsed excitation sources has further increased the reliability and accuracy of each sensor. Finally, after developing sensors capable of monitoring zinc and copper individually, these sensors are combined to form a single optical fiber sensor array capable of simultaneously monitoring concentration changes in zinc and copper in aqueous environments. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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12391 KiB

Open AccessArticle

Algorithm for the Evaluation of Imperfections in Auto Bodywork Using Profiles from a Retroreflective Image

by Ramon Barber, Valerie Zwilling and Miguel A. Salichs

Sensors 2014, 14(2), 2476-2488; https://doi.org/10.3390/s140202476 - 5 Feb 2014

Cited by 3 | Viewed by 5870

Abstract

Nowadays the automobile industry is becoming more and more demanding as far as quality is concerned. Within the wide variety of processes in which this quality must be ensured, those regarding the squeezing of the auto bodywork are especially important due to the [...] Read more.

Nowadays the automobile industry is becoming more and more demanding as far as quality is concerned. Within the wide variety of processes in which this quality must be ensured, those regarding the squeezing of the auto bodywork are especially important due to the fact that the quality of the resulting product is tested manually by experts, leading to inaccuracies of all types. In this paper, an algorithm is proposed for the automated evaluation of the imperfections in the sheets of the bodywork after the squeezing process. The algorithm processes the profile signals from a retroreflective image and characterizes an imperfection. It is based on a convergence criterion that follows the line of the maximum gradient of the imperfection and gives its geometrical characteristics as a result: maximum gradient, length, width, and area. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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Graphical abstract

1257 KiB

Open AccessArticle

RTS Noise and Dark Current White Defects Reduction Using Selective Averaging Based on a Multi-Aperture System

by Bo Zhang, Keiichiro Kagawa, Taishi Takasawa, Min Woong Seo, Keita Yasutomi and Shoji Kawahito

Sensors 2014, 14(1), 1528-1543; https://doi.org/10.3390/s140101528 - 16 Jan 2014

Cited by 13 | Viewed by 9359

Abstract

In extremely low-light conditions, random telegraph signal (RTS) noise and dark current white defects become visible. In this paper, a multi-aperture imaging system and selective averaging method which removes the RTS noise and the dark current white defects by minimizing the synthetic sensor [...] Read more.

In extremely low-light conditions, random telegraph signal (RTS) noise and dark current white defects become visible. In this paper, a multi-aperture imaging system and selective averaging method which removes the RTS noise and the dark current white defects by minimizing the synthetic sensor noise at every pixel is proposed. In the multi-aperture imaging system, a very small synthetic F-number which is much smaller than 1.0 is achieved by increasing optical gain with multiple lenses. It is verified by simulation that the effective noise normalized by optical gain in the peak of noise histogram is reduced from 1.38e⁻ to 0.48 e⁻ in a 3 × 3-aperture system using low-noise CMOS image sensors based on folding-integration and cyclic column ADCs. In the experiment, a prototype 3 × 3-aperture camera, where each aperture has 200 × 200 pixels and an imaging lens with a focal length of 3.0 mm and F-number of 3.0, is developed. Under a low-light condition, in which the maximum average signal is 11e⁻ per aperture, the RTS and dark current white defects are removed and the peak signal-to-noise ratio (PSNR) of the image is increased by 6.3 dB. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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888 KiB

Open AccessArticle

Sensitivity Distribution Properties of a Phase-Shifted Fiber Bragg Grating Sensor to Ultrasonic Waves

by Qi Wu, Yoji Okabe, Kazuya Saito and Fengming Yu

Sensors 2014, 14(1), 1094-1105; https://doi.org/10.3390/s140101094 - 9 Jan 2014

Cited by 36 | Viewed by 7085

Abstract

In this research, the sensitivity distribution properties of a phase-shifted fiber Bragg grating (PS-FBG) to ultrasonic waves were investigated employing the surface attachment method. A careful consideration was taken and examined by experimental results to explain that the distances and angles between the [...] Read more.

In this research, the sensitivity distribution properties of a phase-shifted fiber Bragg grating (PS-FBG) to ultrasonic waves were investigated employing the surface attachment method. A careful consideration was taken and examined by experimental results to explain that the distances and angles between the sensor and ultrasonic source influence not only the amplitudes, but also the initial phases, waveforms, and spectra of detected signals. Furthermore, factors, including the attachment method and the material’s geometric dimensions, were also discussed. Although these results were obtained based on PS-FBG, they are also applicable to a normal FBG sensor or even an optical fiber sensor, due to the identical physical changes induced by ultrasonic waves in all three. Thus, these results are useful for applications of optical fiber sensors in non-destructive testing and structural health monitoring. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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577 KiB

Open AccessArticle

Remote Management for Multipoint Sensing Systems Using Hetero-Core Spliced Optical Fiber Sensors

by Lee See Goh, Yuji Anoda, Watanabe Kazuhiro and Norihiko Shinomiya

Sensors 2014, 14(1), 468-477; https://doi.org/10.3390/s140100468 - 27 Dec 2013

Cited by 5 | Viewed by 6478

Abstract

This paper describes the design and experimental verification of a multipoint sensing system with hetero-core spliced optical fiber sensors and its remote management using an internet-standard protocol. The study proposes two different types of design and conducts experiments to verify those systems’ feasibility. [...] Read more.

This paper describes the design and experimental verification of a multipoint sensing system with hetero-core spliced optical fiber sensors and its remote management using an internet-standard protocol. The study proposes two different types of design and conducts experiments to verify those systems’ feasibility. In order to manage the sensing systems remotely, the management method uses a standard operation and maintenance protocol for internet: the Simple Network Management Protocol is proposed. The purpose of this study is to construct a multipoint sensing system remote management tool by which the system can also determine the status and the identity of fiber optic sensors. The constructed sensing systems are verified and the results have demonstrated that the first proposed system can distinguish the responses from different hetero-core spliced optical fiber sensors remotely. The second proposed system shows that data communications are performed successfully while identifying the status of hetero-core spliced optical fiber sensors remotely. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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764 KiB

Open AccessArticle

The Performance Analysis of Distributed Brillouin Corrosion Sensors for Steel Reinforced Concrete Structures

by Heming Wei, Xuefeng Zhao, Xianglong Kong, Pinglei Zhang, Yanjun Cui and Changsen Sun

Sensors 2014, 14(1), 431-442; https://doi.org/10.3390/s140100431 - 27 Dec 2013

Cited by 36 | Viewed by 7516

Abstract

The Brillouin optical time-domain analysis (BOTDA)-based optical fiber method has been proposed to measure strain variations caused by corrosion expansion. Spatial resolutions of 1 m can be achieved with this kind of Brillouin sensor for detecting the distributed strain. However, when the sensing [...] Read more.

The Brillouin optical time-domain analysis (BOTDA)-based optical fiber method has been proposed to measure strain variations caused by corrosion expansion. Spatial resolutions of 1 m can be achieved with this kind of Brillouin sensor for detecting the distributed strain. However, when the sensing fiber is wound around the steel rebar in a number of circles in a range of several meters, this spatial resolution still has limitations for corrosion monitoring. Here, we employed a low-coherent fiber-optic strain sensor (LCFS) to survey the performance of Brillouin sensors based on the fact that the deformation measured by the LCFS equals the integral of the strains obtained from Brillouin sensors. An electrochemical accelerated corrosion experiment was carried out and the corrosion expansion was monitored by both BOTDA and the LCFS. Results demonstrated that the BOTDA can only measure the expansion strain of about 1,000 με, which was generated by the 18 mm steel rebar corrosion, but, the LCFS had high sensitivity from the beginning of corrosion to the destruction of the structure, and no obvious difference in expansion speed was observed during the acceleration stage of the corrosion developed in the reinforced concrete (RC) specimens. These results proved that the BOTDA method could only be employed to monitor the corrosion inside the structure in the early stage. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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687 KiB

Open AccessArticle

Application of Remote Power-by-Light Switching in a Simplified BOTDA Sensor Network

by Mikel Bravo, Angel Ullan, Ander Zornoza, Alayn Loayssa, Manuel Lopez-Amo and Jose Miguel Lopez-Higuera

Sensors 2013, 13(12), 17434-17444; https://doi.org/10.3390/s131217434 - 17 Dec 2013

Cited by 6 | Viewed by 6190

Abstract

We propose and demonstrate the use of spatial multiplexing as a means to reduce the costs of distributed sensing networks. We propose a new scheme in which remote power-by-light switching is deployed to scan multiple branches of a distributed sensing network based on [...] Read more.

We propose and demonstrate the use of spatial multiplexing as a means to reduce the costs of distributed sensing networks. We propose a new scheme in which remote power-by-light switching is deployed to scan multiple branches of a distributed sensing network based on Brillouin Optical Time Domain Analysis (BOTDA) sensors. A proof-of-concept system is assembled with two 5-km sensor fiber branches that are alternatively monitored using a fast remotely controlled and optically powered optical switch. The multiplexed distributed sensor fibers were located 10 km away from the interrogation unit and a Raman pump is used to remotely power the switch. Furthermore, the deployed BOTDA unit uses an alternative configuration that can lead to simplified setups. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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626 KiB

Open AccessArticle

Capability for Fine Tuning of the Refractive Index Sensing Properties of Long-Period Gratings by Atomic Layer Deposited Al₂O₃ Overlays

by Mateusz Śmietana, Marcin Myśliwiec, Predrag Mikulic, Bartłomiej S. Witkowski and Wojtek J. Bock

Sensors 2013, 13(12), 16372-16383; https://doi.org/10.3390/s131216372 - 28 Nov 2013

Cited by 49 | Viewed by 7872

Abstract

This work presents an application of thin aluminum oxide (Al₂O₃) films obtained using atomic layer deposition (ALD) for fine tuning the spectral response and refractive-index (RI) sensitivity of long-period gratings (LPGs) induced in optical fibers. The technique allows for [...] Read more.

This work presents an application of thin aluminum oxide (Al₂O₃) films obtained using atomic layer deposition (ALD) for fine tuning the spectral response and refractive-index (RI) sensitivity of long-period gratings (LPGs) induced in optical fibers. The technique allows for an efficient and well controlled deposition at monolayer level (resolution ~ 0.12 nm) of excellent quality nano-films as required for optical sensors. The effect of Al₂O₃ deposition on the spectral properties of the LPGs is demonstrated experimentally and numerically. We correlated both the increase in Al₂O₃ thickness and changes in optical properties of the film with the shift of the LPG resonance wavelength and proved that similar films are deposited on fibers and oxidized silicon reference samples in the same process run. Since the thin overlay effectively changes the distribution of the cladding modes and thus also tunes the device’s RI sensitivity, the tuning can be simply realized by varying number of cycles, which is proportional to thickness of the high-refractive-index (n > 1.6 in infrared spectral range) Al₂O₃ film. The advantage of this approach is the precision in determining the film properties resulting in RI sensitivity of the LPGs. To the best of our knowledge, this is the first time that an ultra-precise method for overlay deposition has been applied on LPGs for RI tuning purposes and the results have been compared with numerical simulations based on LP mode approximation. Full article

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2151 KiB

Open AccessArticle

Long-Wavelength Infrared Sensing by Cytochrome C Protein Thin Film Deposited by the Spin Coating Method

by Bo-Yu Lai, Chung-Hao Chu and Guo-Dung John Su

Sensors 2013, 13(11), 15833-15845; https://doi.org/10.3390/s131115833 - 20 Nov 2013

Cited by 5 | Viewed by 6584

Abstract

High infrared absorption, large temperature coefficient of resistance (TCR) and small 1/f noise are preferred characteristics for sensing materials used in bolometers. In this paper, we discuss a cytochrome c protein as a potential sensing material for long-wavelength bolometers. We simulated and experimentally [...] Read more.

High infrared absorption, large temperature coefficient of resistance (TCR) and small 1/f noise are preferred characteristics for sensing materials used in bolometers. In this paper, we discuss a cytochrome c protein as a potential sensing material for long-wavelength bolometers. We simulated and experimentally proved high infrared absorption of cytochrome c in the wavelength between 8 μm and 14 μm. Cytochrome c thin films were deposited on a hydrophilic surface using the spin coating method. The resistance variation with temperature is measured and we show that the TCR of cytochrome c thin films is consistently higher than 20%. The measured values of 1/f noise were as low as 2.33 × 10^–¹³ V²/Hz at 60 Hz. Finally, we test the reliability of cytochrome c by measuring the resistance changes over time under varying conditions. We found that cytochrome c thin films deteriorated significantly without appropriate packaging. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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971 KiB

Open AccessArticle

Performance of a Distributed Simultaneous Strain and Temperature Sensor Based on a Fabry-Perot Laser Diode and a Dual-Stage FBG Optical Demultiplexer

by Suhwan Kim, Hyungwoo Kwon, Injae Yang, Seungho Lee, Jeehyun Kim and Shinwon Kang

Sensors 2013, 13(11), 15452-15464; https://doi.org/10.3390/s131115452 - 12 Nov 2013

Cited by 8 | Viewed by 7119

Abstract

A simultaneous strain and temperature measurement method using a Fabry-Perot laser diode (FP-LD) and a dual-stage fiber Bragg grating (FBG) optical demultiplexer was applied to a distributed sensor system based on Brillouin optical time domain reflectometry (BOTDR). By using a Kalman filter, we [...] Read more.

A simultaneous strain and temperature measurement method using a Fabry-Perot laser diode (FP-LD) and a dual-stage fiber Bragg grating (FBG) optical demultiplexer was applied to a distributed sensor system based on Brillouin optical time domain reflectometry (BOTDR). By using a Kalman filter, we improved the performance of the FP-LD based OTDR, and decreased the noise using the dual-stage FBG optical demultiplexer. Applying the two developed components to the BOTDR system and using a temperature compensating algorithm, we successfully demonstrated the simultaneous measurement of strain and temperature distributions under various experimental conditions. The observed errors in the temperature and strain measured using the developed sensing system were 0.6 °C and 50 με, and the spatial resolution was 1 m, respectively. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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552 KiB

Open AccessArticle

Monitoring the Evaporation of Fluids from Fiber-Optic Micro-Cell Cavities

by Eyal Preter, Borut Preloznik, Vlada Artel, Chaim N. Sukenik, Denis Donlagic and Avi Zadok

Sensors 2013, 13(11), 15261-15273; https://doi.org/10.3390/s131115261 - 7 Nov 2013

Cited by 31 | Viewed by 6631

Abstract

Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in [...] Read more.

Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identification of fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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424 KiB

Open AccessArticle

A Highly Sensitive Refractometric Sensor Based on Cascaded SiN Microring Resonators

by Vanessa Zamora, Peter Lützow, Martin Weiland and Daniel Pergande

Sensors 2013, 13(11), 14601-14610; https://doi.org/10.3390/s131114601 - 28 Oct 2013

Cited by 23 | Viewed by 7863

Abstract

We investigate a highly sensitive optical sensor based on two cascaded microring resonators exploiting the Vernier effect. The architecture consists of two microrings with a slight difference in their free spectral ranges. This allows the generation of the Vernier effect for achieving ultra-high [...] Read more.

We investigate a highly sensitive optical sensor based on two cascaded microring resonators exploiting the Vernier effect. The architecture consists of two microrings with a slight difference in their free spectral ranges. This allows the generation of the Vernier effect for achieving ultra-high sensitivities. The sensor chip was fabricated using a silicon nitride platform and characterized with isopropanol/ethanol mixtures. A sensitivity of 0.95 nm/% was found for isopropanol concentrations in ethanol ranging from 0% to 10%. Furthermore, a collection of measurements was carried out using aqueous sodium chloride (NaCl) in solutions of different concentrations, confirming a high sensitivity of 10.3 nm/% and a bulk refractive index sensitivity of 6,317 nm/RIU. A limit of detection of 3.16 ´ 10⁻⁶ RIU was determined. These preliminary results show the potential features of cascaded silicon nitride microring resonators for real-time and free-label monitoring of biomolecules for a broad range of applications. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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715 KiB

Open AccessArticle

Plastic Optical Fibre Sensor for Spine Bending Monitoring with Power Fluctuation Compensation

by Mohd Anwar Zawawi, Sinead O'Keeffe and Elfed Lewis

Sensors 2013, 13(11), 14466-14483; https://doi.org/10.3390/s131114466 - 25 Oct 2013

Cited by 36 | Viewed by 7929

Abstract

This paper presents the implementation of power fluctuation compensation for an intensity-based optical fibre bending sensor aimed at monitoring human spine bending in a clinical environment. To compensate for the light intensity changes from the sensor light source, a reference signal was provided [...] Read more.

This paper presents the implementation of power fluctuation compensation for an intensity-based optical fibre bending sensor aimed at monitoring human spine bending in a clinical environment. To compensate for the light intensity changes from the sensor light source, a reference signal was provided via the light reflection from an aluminum foil surface fixed at a certain distance from the source fibre end tips. From the results, it was found that the investigated sensor compensation technique was capable of achieving a 2° resolution for a bending angle working range between 0° and 20°. The study also suggested that the output voltage ratio has a 0.55% diversion due to input voltage variation between 2.9 V and 3.4 V and a 0.25% output drift for a 2 h measurement. With the achieved sensor properties, human spine monitoring in a clinical environment can potentially be implemented using this approach with power fluctuation compensation. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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1344 KiB

Open AccessArticle

A Highly Sensitive Fiber Optic Sensor Based on Two-Core Fiber for Refractive Index Measurement

by José Rafael Guzmán-Sepúlveda, Rafael Guzmán-Cabrera, Miguel Torres-Cisneros, José Javier Sánchez-Mondragón and Daniel Alberto May-Arrioja

Sensors 2013, 13(10), 14200-14213; https://doi.org/10.3390/s131014200 - 22 Oct 2013

Cited by 33 | Viewed by 8263

Abstract

A simple and compact fiber optic sensor based on a two-core fiber is demonstrated for high-performance measurements of refractive indices (RI) of liquids. In order to demonstrate the suitability of the proposed sensor to perform high-sensitivity sensing in a variety of applications, the [...] Read more.

A simple and compact fiber optic sensor based on a two-core fiber is demonstrated for high-performance measurements of refractive indices (RI) of liquids. In order to demonstrate the suitability of the proposed sensor to perform high-sensitivity sensing in a variety of applications, the sensor has been used to measure the RI of binary liquid mixtures. Such measurements can accurately determine the salinity of salt water solutions, and detect the water content of adulterated alcoholic beverages. The largest sensitivity of the RI sensor that has been experimentally demonstrated is 3,119 nm per Refractive Index Units (RIU) for the RI range from 1.3160 to 1.3943. On the other hand, our results suggest that the sensitivity can be enhanced up to 3485.67 nm/RIU approximately for the same RI range. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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409 KiB

Open AccessCommunication

Highly Sensitive Refractive Index Sensor Based on Adiabatically Tapered Microfiber Long Period Gratings

by Wen Bin Ji, Swee Chuan Tjin, Bo Lin and Choong Leng Ng

Sensors 2013, 13(10), 14055-14063; https://doi.org/10.3390/s131014055 - 17 Oct 2013

Cited by 33 | Viewed by 7605

Abstract

We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss [...] Read more.

We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss is sufficiently small. The boron and germanium co-doped inner cladding makes it suitable for inscribing gratings into its tapered form. The manner of wavelength shift for refractive indices (RIs) differs from conventional LPG, and the refractive index detection limit is 1.67 × 10⁻⁵. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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433 KiB

Open AccessArticle

A Temperature Sensor Based on a Polymer Optical Fiber Macro-Bend

by Alberto Tapetado Moraleda, Carmen Vázquez García, Joseba Zubia Zaballa and Jon Arrue

Sensors 2013, 13(10), 13076-13089; https://doi.org/10.3390/s131013076 - 26 Sep 2013

Cited by 74 | Viewed by 10502

Abstract

The design and development of a plastic optical fiber (POF) macrobend temperature sensor is presented. The sensor has a linear response versus temperature at a fixed bend radius, with a sensitivity of . The sensor system used a dummy fiber-optic sensor for reference [...] Read more.

The design and development of a plastic optical fiber (POF) macrobend temperature sensor is presented. The sensor has a linear response versus temperature at a fixed bend radius, with a sensitivity of . The sensor system used a dummy fiber-optic sensor for reference purposes having a resolution below 0.3 °C. A comprehensive experimental analysis was carried out to provide insight into the effect of different surrounding media on practical macro-bend POF sensor implementation. Experimental results are successfully compared with bend loss calculations. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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391 KiB

Open AccessArticle

Quantitative Assessment of Birefringent Skin Structures in Scattered Light Confocal Imaging Using Radially Polarized Light

by Babu Varghese, Rieko Verhagen, Altaf Hussain, Clemence Boudot, Qiangqiang Tai, Siqi Ding, Jasmin Alexandra Holz and Natallia Eduarda Uzunbajakava

Sensors 2013, 13(9), 12527-12535; https://doi.org/10.3390/s130912527 - 17 Sep 2013

Cited by 4 | Viewed by 8058

Abstract

The polarization characteristics of birefringent tissues could be only partially obtained using linearly polarized light in polarization sensitive optical imaging. Here we analyze the change in polarization of backscattered light from birefringent structures versus the orientations of the incident polarizations using linearly, circularly [...] Read more.

The polarization characteristics of birefringent tissues could be only partially obtained using linearly polarized light in polarization sensitive optical imaging. Here we analyze the change in polarization of backscattered light from birefringent structures versus the orientations of the incident polarizations using linearly, circularly and radially polarized light in a cross-polarized confocal microscope. A spatially variable retardation plate composed of eight sectors of λ/2 wave plates was used to transform linearly polarized light into a radially polarized light. Based on the experimental data obtained from ex-vivo measurements on human scalp hairs and in-vivo measurements on hair and skin, we exemplify that the underestimation of the birefringence content resulting from the orientation related effects associated with the use of linearly polarized light for imaging tissues containing wavy birefringent structures could be minimized by using radially polarized light. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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769 KiB

Open AccessArticle

Characterization of Flexible Copolymer Optical Fibers for Force Sensing Applications

by Marek Krehel, René M. Rossi, Gian-Luca Bona and Lukas J. Scherer

Sensors 2013, 13(9), 11956-11968; https://doi.org/10.3390/s130911956 - 9 Sep 2013

Cited by 31 | Viewed by 12875

Abstract

In this paper, different polymer optical fibres for applications in force sensing systems in textile fabrics are reported. The proposed method is based on the deflection of the light in fibre waveguides. Applying a force on the fibre changes the geometry and affects [...] Read more.

In this paper, different polymer optical fibres for applications in force sensing systems in textile fabrics are reported. The proposed method is based on the deflection of the light in fibre waveguides. Applying a force on the fibre changes the geometry and affects the wave guiding properties and hence induces light loss in the optical fibre. Fibres out of three different elastic and transparent copolymer materials were successfully produced and tested. Moreover, the influence of the diameter on the sensing properties was studied. The detectable force ranges from 0.05 N to 40 N (applied on 3 cm of fibre length), which can be regulated with the material and the diameter of the fibre. The detected signal loss varied from 0.6% to 78.3%. The fibres have attenuation parameters between 0.16–0.25 dB/cm at 652 nm. We show that the cross-sensitivies to temperature, strain and bends are low. Moreover, the high yield strength (0.0039–0.0054 GPa) and flexibility make these fibres very attractive candidates for integration into textiles to form wearable sensors, medical textiles or even computing systems. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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830 KiB

Open AccessArticle

A Noncontact Force Sensor Based on a Fiber Bragg Grating and Its Application for Corrosion Measurement

by Clara J. Pacheco and Antonio C. Bruno

Sensors 2013, 13(9), 11476-11489; https://doi.org/10.3390/s130911476 - 29 Aug 2013

Cited by 29 | Viewed by 8624

Abstract

A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining [...] Read more.

A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining the sensor at a constant standoff distance, material loss due to corrosion increases the distance between the magnet and the corroded surface, which decreases the magnetic force. This will decrease the strain in the optical fiber shifting the reflected Bragg wavelength. The measured shift for the optical fiber used was 1.36 nm per Newton. Models were developed to optimize the magnet geometry for a specific sensor standoff distance and for particular corrosion pit depths. The sensor was able to detect corrosion pits on a fuel storage tank bottom with depths in the sub-millimeter range. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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Review

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1213 KiB

Open AccessReview

Chronology of Fabry-Perot Interferometer Fiber-Optic Sensors and Their Applications: A Review

by Md. Rajibul Islam, Muhammad Mahmood Ali, Man-Hong Lai, Kok-Sing Lim and Harith Ahmad

Sensors 2014, 14(4), 7451-7488; https://doi.org/10.3390/s140407451 - 24 Apr 2014

Cited by 332 | Viewed by 28036

Abstract

Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and [...] Read more.

Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and voltage. During this time, numerous types of interferometers have been developed such as Fabry-Perot, Michelson, Mach-Zehnder, Sagnac Fiber, and Common-path interferometers. Fabry-Perot interferometer (FPI) fiber-optic sensors have been extensively investigated for their exceedingly effective, simple fabrication as well as low cost aspects. In this study, a wide variety of FPI sensors are reviewed in terms of fabrication methods, principle of operation and their sensing applications. The chronology of the development of FPI sensors and their implementation in various applications are discussed. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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1159 KiB

Open AccessReview

Microfiber Optical Sensors: A Review

by Jingyi Lou, Yipei Wang and Limin Tong

Sensors 2014, 14(4), 5823-5844; https://doi.org/10.3390/s140405823 - 25 Mar 2014

Cited by 216 | Viewed by 17226

Abstract

With diameter close to or below the wavelength of guided light and high index contrast between the fiber core and the surrounding, an optical microfiber shows a variety of interesting waveguiding properties, including widely tailorable optical confinement, evanescent fields and waveguide dispersion. Among [...] Read more.

With diameter close to or below the wavelength of guided light and high index contrast between the fiber core and the surrounding, an optical microfiber shows a variety of interesting waveguiding properties, including widely tailorable optical confinement, evanescent fields and waveguide dispersion. Among various microfiber applications, optical sensing has been attracting increasing research interest due to its possibilities of realizing miniaturized fiber optic sensors with small footprint, high sensitivity, fast response, high flexibility and low optical power consumption. Here we review recent progress in microfiber optical sensors regarding their fabrication, waveguide properties and sensing applications. Typical microfiber-based sensing structures, including biconical tapers, optical gratings, circular cavities, Mach-Zehnder interferometers and functionally coated/doped microfibers, are summarized. Categorized by sensing structures, microfiber optical sensors for refractive index, concentration, temperature, humidity, strain and current measurement in gas or liquid environments are reviewed. Finally, we conclude with an outlook for challenges and opportunities of microfiber optical sensors. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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1114 KiB

Open AccessReview

Recent Advances in Gas and Chemical Detection by Vernier Effect-Based Photonic Sensors

by Mario La Notte, Benedetto Troia, Tommaso Muciaccia, Carlo Edoardo Campanella, Francesco De Leonardis and Vittorio M. N. Passaro

Sensors 2014, 14(3), 4831-4855; https://doi.org/10.3390/s140304831 - 10 Mar 2014

Cited by 63 | Viewed by 10308

Abstract

Recently, the Vernier effect has been proved to be very efficient for significantly improving the sensitivity and the limit of detection (LOD) of chemical, biochemical and gas photonic sensors. In this paper a review of compact and efficient photonic sensors based on the [...] Read more.

Recently, the Vernier effect has been proved to be very efficient for significantly improving the sensitivity and the limit of detection (LOD) of chemical, biochemical and gas photonic sensors. In this paper a review of compact and efficient photonic sensors based on the Vernier effect is presented. The most relevant results of several theoretical and experimental works are reported, and the theoretical model of the typical Vernier effect-based sensor is discussed as well. In particular, sensitivity up to 460 μm/RIU has been experimentally reported, while ultra-high sensitivity of 2,500 μm/RIU and ultra-low LOD of 8.79 × 10⁻⁸ RIU have been theoretically demonstrated, employing a Mach-Zehnder Interferometer (MZI) as sensing device instead of an add drop ring resonator. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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919 KiB

Open AccessReview

Toward a New Generation of Photonic Humidity Sensors

by Stanislav A. Kolpakov, Neil T. Gordon, Chengbo Mou and Kaiming Zhou

Sensors 2014, 14(3), 3986-4013; https://doi.org/10.3390/s140303986 - 26 Feb 2014

Cited by 121 | Viewed by 13737

Abstract

This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity [...] Read more.

This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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Other

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266 KiB

Open AccessLetter

Magnetic Sensing with Ferrofluid and Fiber Optic Connectors

by Daniel Homa and Gary Pickrell

Sensors 2014, 14(3), 3891-3896; https://doi.org/10.3390/s140303891 - 25 Feb 2014

Cited by 24 | Viewed by 9143

Abstract

A simple, cost effective and sensitive fiber optic magnetic sensor fabricated with ferrofluid and commercially available fiber optic components is described in this paper. The system uses a ferrofluid infiltrated extrinsic Fabry-Perot interferometer (EFPI) interrogated with an infrared wavelength spectrometer to measure magnetic [...] Read more.

A simple, cost effective and sensitive fiber optic magnetic sensor fabricated with ferrofluid and commercially available fiber optic components is described in this paper. The system uses a ferrofluid infiltrated extrinsic Fabry-Perot interferometer (EFPI) interrogated with an infrared wavelength spectrometer to measure magnetic flux density. The entire sensing system was developed with commercially available components so it can be easily and economically reproduced in large quantities. The device was tested with two different ferrofluid types over a range of magnetic flux densities to verify performance. The sensors readily detected magnetic flux densities in the range of 0.5 mT to 12.0 mT with measurement sensitivities in the range of 0.3 to 2.3 nm/mT depending on ferrofluid type. Assuming a conservative wavelength resolution of 0.1 nm for state of the art EFPI detection abilities, the estimated achievable measurement resolution is on the order 0.04 mT. The inherent small size and basic structure complimented with the fabrication ease make it well-suited for a wide array of research, industrial, educational and military applications. Full article

(This article belongs to the Special Issue Photonic Sensors for Industrial, Environmental and Health Monitoring)

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