Research

33 pages, 3428 KiB

Open AccessArticle

Optical Waveguides and Integrated Optical Devices for Medical Diagnosis, Health Monitoring and Light Therapies

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Jiayu Wang

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Jianfei Dong

Sensors 2020, 20(14), 3981; https://doi.org/10.3390/s20143981 - 17 Jul 2020

Cited by 34 | Viewed by 6665

Abstract

Optical waveguides and integrated optical devices are promising solutions for many applications, such as medical diagnosis, health monitoring and light therapies. Despite the many existing reviews focusing on the materials that these devices are made from, a systematic review that relates these devices [...] Read more.

Optical waveguides and integrated optical devices are promising solutions for many applications, such as medical diagnosis, health monitoring and light therapies. Despite the many existing reviews focusing on the materials that these devices are made from, a systematic review that relates these devices to the various materials, fabrication processes, sensing methods and medical applications is still seldom seen. This work is intended to link these multidisciplinary fields, and to provide a comprehensive review of the recent advances of these devices. Firstly, the optical and mechanical properties of optical waveguides based on glass, polymers and heterogeneous materials and fabricated via various processes are thoroughly discussed, together with their applications for medical purposes. Then, the fabrication processes and medical implementations of integrated passive and active optical devices with sensing modules are introduced, which can be used in many medical fields such as drug delivery and cardiovascular healthcare. Thirdly, wearable optical sensing devices based on light sensing methods such as colorimetry, fluorescence and luminescence are discussed. Additionally, the wearable optical devices for light therapies are introduced. The review concludes with a comprehensive summary of these optical devices, in terms of their forms, materials, light sources and applications. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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10 pages, 7179 KiB

Open AccessArticle

Realization of Hollow-Core Photonic-Crystal Fiber Optic Gyro Based on Low-Noise Multi-Frequency Lasers with Intermediate-Frequency Difference

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Sensors 2020, 20(10), 2835; https://doi.org/10.3390/s20102835 - 16 May 2020

Cited by 1 | Viewed by 1928

Abstract

Mainly focusing on the demand for a novel resonator optic gyro based on a hollow-core photonic-crystal fiber (HC-RFOG), we achieve a multi-frequency lasers generation with low relative phase noise via an acousto-optic modulation of light from a single laser diode. We design a [...] Read more.

Mainly focusing on the demand for a novel resonator optic gyro based on a hollow-core photonic-crystal fiber (HC-RFOG), we achieve a multi-frequency lasers generation with low relative phase noise via an acousto-optic modulation of light from a single laser diode. We design a homologous heterodyne digital optical phase-locked loop (HHD-OPLL), based on which we realize the low-noise multi-frequency lasers (LNMFLs) with an intermediate frequency difference. The noise between the lasers with a 20 MHz difference is 0.036 Hz, within the bandwidth of 10 Hz, in a tuning range of 120 kHz, approximately 40 dB lower than that produced without the HHD-OPLL. Finally, based on the LNMFLs, an HC-RFOG is realized and a bias stability of 5.8 °/h is successfully demonstrated. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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9 pages, 1390 KiB

Open AccessArticle

Evanescent-Wave Fiber Optic Sensing of the Anionic Dye Uranine Based on Ion Association Extraction

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Takuya Okazaki

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Tomoaki Watanabe

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Hideki Kuramitz

Sensors 2020, 20(10), 2796; https://doi.org/10.3390/s20102796 - 14 May 2020

Cited by 7 | Viewed by 2544

Abstract

Herein, we propose an evanescent-wave fiber optic sensing technique for the anionic dye uranine based on ion association extraction. The sensor was prepared by removing a section of the cladding from a multimode fiber and hydrophobization of the exposed core surface. Uranine was [...] Read more.

Herein, we propose an evanescent-wave fiber optic sensing technique for the anionic dye uranine based on ion association extraction. The sensor was prepared by removing a section of the cladding from a multimode fiber and hydrophobization of the exposed core surface. Uranine was extracted in association along with hexadecyltrimethylammonium (CTA) ion onto the fiber surface and detected via absorption of the evanescent wave generated on the surface of the exposed fiber core. The effect of CTA⁺ concentration added for ion association was investigated, revealing that the absorbance of uranine increased with increasing CTA⁺ concentration. A change in the sensor response as a function of the added uranine concentration was clearly observed. The extraction data were analyzed using a distribution equilibrium model and a Freundlich isotherm. The uranine concentration in the evanescent field of the fiber optic was up to 54 times higher than that in the bulk solution, and the limit of detection (3σ) for uranine was found to be 1.3 nM. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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8 pages, 1759 KiB

Open AccessArticle

Ultrahigh Resolution Thickness Measurement Technique Based on a Hollow Core Optical Fiber Structure

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Sensors 2020, 20(7), 2035; https://doi.org/10.3390/s20072035 - 04 Apr 2020

Cited by 5 | Viewed by 2434

Abstract

An ultrahigh resolution thickness measurement sensor was proposed based on a single mode–hollow core–single mode (SMF–HCF–SMF) fiber structure by coating a thin layer of material on the HCF surface. Theoretical analysis shows that the SMF–HCF–SMF fiber structure can measure coating thickness down to [...] Read more.

An ultrahigh resolution thickness measurement sensor was proposed based on a single mode–hollow core–single mode (SMF–HCF–SMF) fiber structure by coating a thin layer of material on the HCF surface. Theoretical analysis shows that the SMF–HCF–SMF fiber structure can measure coating thickness down to sub-nanometers. An experimental study was carried out by coating a thin layer of graphene oxide (GO) on the HCF surface of the fabricated SMF–HCF–SMF fiber structure. The experimental results show that the fiber sensor structure can detect a thin layer with a thickness down to 0.21 nanometers, which agrees well with the simulation results. The proposed sensing technology has the advantages of simple configuration, ease of fabrication, low cost, high resolution, and good repeatability, which offer great potential for practical thickness measurement applications. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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31 pages, 10669 KiB

Open AccessEditor’s ChoiceArticle

The Field Monitoring Experiment of the Roof Strata Movement in Coal Mining Based on DFOS

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Tao Hu

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Gongyu Hou

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Zixiang Li

Sensors 2020, 20(5), 1318; https://doi.org/10.3390/s20051318 - 28 Feb 2020

Cited by 28 | Viewed by 3498

Abstract

Mining deformation of roof strata is the main cause of methane explosion, water inrush, and roof collapse accidents amid underground coal mining. To ensure the safety of coal mining, the distributed optical fiber sensor (DFOS) technology has been applied in the 150,313 working [...] Read more.

Mining deformation of roof strata is the main cause of methane explosion, water inrush, and roof collapse accidents amid underground coal mining. To ensure the safety of coal mining, the distributed optical fiber sensor (DFOS) technology has been applied in the 150,313 working face by Yinying Coal Mine in Shanxi Province, north China to monitor the roof strata movement, so as to grasp the movement law of roof strata and make it serve for production. The optical fibers are laid out in the holes drilled through the overlying strata on the roadway roof and BOTDR technique is utilized to carry out the on-site monitoring. Prior to the on-site test, the coupling test of the fiber strain in the concrete anchorage, the calibration test of the fiber strain coefficient of the 5-mm steel strand (SS) fiber, and the test of the strain transfer performance of the SS fiber were carried out in the laboratory. The approaches for fiber laying-out in the holes and fiber’s spatial positioning underground the coal mine have been optimized in the field. The indoor test results show that the high-strength SS optical fiber has a high strain transfer performance, which can be coupled with the concrete anchor with uniform deformation. This demonstrated the feasibility of SS fiber for monitoring strata movement theoretically and experimentally; and the law of roof strata fracturing and collapse is obtained from the field test results. This paper is a trial to study the whole process of dynamic movement of the deformation of roof strata. Eventually the study results will help Yinying Coal Mine to optimize mining design, prevent coal mine accidents, and provide detailed test basis for DFOS monitoring technique of roof strata movement. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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13 pages, 3531 KiB

Open AccessArticle

Ethanol Gas Sensitivity Sensor Based on Roughened POF Taper of Modified Polypyrrole Films

by

Wenyi Liu

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Yanjun Hu

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Yulong Hou

Sensors 2020, 20(4), 989; https://doi.org/10.3390/s20040989 - 12 Feb 2020

Cited by 11 | Viewed by 2473

Abstract

The three polypyrrole (PPy) films with different mixture ratios, namely PPy1, PPy2, and PPy3, were synthesized by chemical oxidation with pyrrole and ferric chloride (FeCl₃). The roughened plastic optical fiber (POF) taper assembled PPy films (POF-PPy1, POF-PPy2, and POF-PPy3) were facilely [...] Read more.

The three polypyrrole (PPy) films with different mixture ratios, namely PPy1, PPy2, and PPy3, were synthesized by chemical oxidation with pyrrole and ferric chloride (FeCl₃). The roughened plastic optical fiber (POF) taper assembled PPy films (POF-PPy1, POF-PPy2, and POF-PPy3) were facilely prepared and bent U shape structure for testing ethanol gas at room temperature. The morphologies of the PPy films and the roughened POF taper were studied using electron microscopy. The effect of the three PPy films on the gas response was investigated and the results showed that the POF-PPy2 exhibited a high sensitivity of 5.08 × 10⁻⁵ dB/ppm. The detection limit of the sensor was 140 ppm and its response and recovery times were 5 s and 8 s, respectively. The results also showed that as the bending radius decreased, the response and recovery times gradually shortened, while the output power increased. In addition, the proposed sensor has advantages of a low cost and simple structure. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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15 pages, 2745 KiB

Open AccessArticle

Long-Range Distributed Solar Irradiance Sensing Using Optical Fibers

by

Regina Magalhães

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Luis Costa

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Sonia Martin-Lopez

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Miguel Gonzalez-Herraez

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Alejandro F. Braña

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Hugo F. Martins

Sensors 2020, 20(3), 908; https://doi.org/10.3390/s20030908 - 08 Feb 2020

Cited by 5 | Viewed by 2822

Abstract

Until recently, the amount of solar irradiance reaching the Earth surface was considered to be a steady value over the years. However, there is increasing observational evidence showing that this quantity undergoes substantial variations over time, which need to be addressed in different [...] Read more.

Until recently, the amount of solar irradiance reaching the Earth surface was considered to be a steady value over the years. However, there is increasing observational evidence showing that this quantity undergoes substantial variations over time, which need to be addressed in different scenarios ranging from climate change to solar energy applications. With the growing interest in developing solar energy technology with enhanced efficiency and optimized management, the monitoring of solar irradiance at the ground level is now considered to be a fundamental input in the pursuit of that goal. Here, we propose the first fiber-based distributed sensor able of monitoring ground solar irradiance in real time, with meter scale spatial resolutions over distances of several tens of kilometers (up to 100 km). The technique is based on an optical fiber reflectometry technique (CP-ϕOTDR), which enables real time and long-range high-sensitivity bolometric measurements of solar radiance with a single optical fiber cable and a single interrogator unit. The method is explained and analyzed theoretically. A validation of the method is proposed using a solar simulator irradiating standard optical fibers, where we demonstrate the ability to detect and quantify solar irradiance with less than a 0.1 W/m² resolution. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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16 pages, 6175 KiB

Open AccessArticle

Use of Miniature Step Gauges to Assess the Performance of 3D Optical Scanners and to Evaluate the Accuracy of a Novel Additive Manufacture Process

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Maria Grazia Guerra

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Leonardo De Chiffre

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Fulvio Lavecchia

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Luigi Maria Galantucci

Sensors 2020, 20(3), 738; https://doi.org/10.3390/s20030738 - 29 Jan 2020

Cited by 11 | Viewed by 2215

Abstract

In this work, we show how miniature step gauges featuring unidirectional and bidirectional lengths can be used to assess the performance of 3D optical scanners as well as the accuracy of novel Additive Manufacturing (AM) processes. A miniature step gauge made of black [...] Read more.

In this work, we show how miniature step gauges featuring unidirectional and bidirectional lengths can be used to assess the performance of 3D optical scanners as well as the accuracy of novel Additive Manufacturing (AM) processes. A miniature step gauge made of black polyphenylene sulfide (PPS) was used for the performance verification of three different optical scanners: a structured light scanner (SLS), a laser line scanner (LLS), and a photogrammetry-based scanner (PSSRT), having comparable resolutions and working volumes. Results have shown a good agreement between the involved scanners, with errors below 5 μm and expanded uncertainties below 10 μm. The step gauge geometry due to the bidirectional lengths, highlights that there is a different interaction between the optical properties of the step gauge under measurement and each optical instrument involved and this aspect has to be considered in the uncertainty budget. The same geometry, due to its great significance in the detection of systematic errors, was used, as a novelty, to evaluate the accuracy of Lithography-based Ceramics Manufacturing (LCM), a proprietary additive manufacturing technology used for the fabrication of medical implants. In particular, two miniature step gauges made of Tricalcium Phosphate (TCP) were produced. Measurements conducted with the SLS scanner were characterized by a negligible error and by an uncertainty of about 5 μm. Deviations of the manufactured step gauges with respect to the Computer Aided Designed (CAD) model were comprised between ±50 μm, with positive deviations in the order of 100 μm on vertical sides. Differences in the order of 50 μm between the two step gauges were registered. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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17 pages, 4002 KiB

Open AccessArticle

Manufacturing and Characterization of Femtosecond Laser-Inscribed Bragg Grating in Polymer Waveguide Operation in an IR-A Wavelength Range

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Sensors 2020, 20(1), 249; https://doi.org/10.3390/s20010249 - 01 Jan 2020

Cited by 5 | Viewed by 2458

Abstract

Optical sensors, such as fiber Bragg gratings, offer advantages compared to other sensors in many technological fields due to their outstanding characteristics. This sensor technology is currently transferred to polymer waveguides that provide the potential for cost-effective, easy, and flexible manufacturing of planar [...] Read more.

Optical sensors, such as fiber Bragg gratings, offer advantages compared to other sensors in many technological fields due to their outstanding characteristics. This sensor technology is currently transferred to polymer waveguides that provide the potential for cost-effective, easy, and flexible manufacturing of planar structures. While sensor production itself, in the majority of cases, is performed by means of phase mask technique, which is limited in terms of its degrees of freedom, other inscription techniques enable the manufacture of more adaptable sensor elements for a wider range of applications. In this article, we demonstrate the point-by-point femtosecond laser direct inscription method for the processing of polymer Bragg gratings into waveguides of the epoxy-based negative photoresist material EpoCore for a wavelength range around 850 nm. By characterizing the obtained grating back-reflection of the produced sensing element, we determined the sensitivity for the state variables temperature, humidity, and strain to be 45 pm/K, 19 pm/%, and 0.26 pm/µε, respectively. Individual and more complex grating structures can be developed from this information, thus opening new fields of utilization. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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18 pages, 4423 KiB

Open AccessArticle

Optical Harmonic Vernier Effect: A New Tool for High Performance Interferometric Fiber Sensors

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Sensors 2019, 19(24), 5431; https://doi.org/10.3390/s19245431 - 09 Dec 2019

Cited by 70 | Viewed by 5097

Abstract

The optical Vernier effect magnifies the sensing capabilities of an interferometer, allowing for unprecedented sensitivities and resolutions to be achieved. Just like a caliper uses two different scales to achieve higher resolution measurements, the optical Vernier effect is based on the overlap in [...] Read more.

The optical Vernier effect magnifies the sensing capabilities of an interferometer, allowing for unprecedented sensitivities and resolutions to be achieved. Just like a caliper uses two different scales to achieve higher resolution measurements, the optical Vernier effect is based on the overlap in the responses of two interferometers with slightly detuned interference signals. Here, we present a novel approach in detail, which introduces optical harmonics to the Vernier effect through Fabry–Perot interferometers, where the two interferometers can have very different frequencies in the interferometric pattern. We demonstrate not only a considerable enhancement compared to current methods, but also better control of the sensitivity magnification factor, which scales up with the order of the harmonics, allowing us to surpass the limits of the conventional Vernier effect as used today. In addition, this novel concept opens also new ways of dimensioning the sensing structures, together with improved fabrication tolerances. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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9 pages, 1520 KiB

Open AccessArticle

Temperature-Independent Gas Pressure Sensor with High Birefringence Photonic Crystal Fiber-Based Reflective Lyot Filter

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Bo Huang

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Ying Wang

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Chun Mao

Sensors 2019, 19(23), 5312; https://doi.org/10.3390/s19235312 - 02 Dec 2019

Cited by 11 | Viewed by 3148

Abstract

A novel temperature-independent gas pressure sensor based on a reflective fiber Lyot filter is presented in this paper. The reflective fiber Lyot filter is simply consist of a fiber polarizer and a segment of hollow-core photonic bandgap fiber (HB-PCF). The HB-PCF plays the [...] Read more.

A novel temperature-independent gas pressure sensor based on a reflective fiber Lyot filter is presented in this paper. The reflective fiber Lyot filter is simply consist of a fiber polarizer and a segment of hollow-core photonic bandgap fiber (HB-PCF). The HB-PCF plays the role of birefringent cavity in the reflective fiber Lyot filter and works as the sensor head in the gas pressure sensor. Experiment results show that the responses of the sensor to gas pressure and temperature are 3.94 nm/MPa and −0.009 nm/°C, indicating that the proposed gas pressure is sensitive to gas pressure rather than temperature. Coupled with the advantages of simple structure, easy manufacture, high sensitivity and temperature independent, the proposed reflective fiber Lyot filter-based gas pressure sensor holds great potential application in the field of gas pressure monitoring. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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13 pages, 5881 KiB

Open AccessArticle

Simultaneous Temperature and Strain Measurements Using Polarization-Maintaining Few-Mode Bragg Gratings

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Sensors 2019, 19(23), 5221; https://doi.org/10.3390/s19235221 - 28 Nov 2019

Cited by 9 | Viewed by 2239

Abstract

Simultaneous measurement of temperature and strain was demonstrated using a polarization-maintaining few-mode Bragg grating (PM-FMF-FBG) based on the wavelength and phase modulation of the even

L P_{11}

mode. The wavelength shift sensitivity and the interrogated phase sensitivity of the temperature and strain [...] Read more.

Simultaneous measurement of temperature and strain was demonstrated using a polarization-maintaining few-mode Bragg grating (PM-FMF-FBG) based on the wavelength and phase modulation of the even

L P_{11}

mode. The wavelength shift sensitivity and the interrogated phase sensitivity of the temperature and strain were measured to be 10 pm·°C⁻¹ and 0.73 pm·με⁻¹ and −3.2 × 10⁻² rad·°C⁻¹ and 4 × 10⁻⁴ rad·με⁻¹, respectively, with a discrimination efficiency of 98%. The polarization interference led to selective polarization excitation of the reflection spectra, and the calculated phase sensitivity agreed with the experimental results. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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22 pages, 8051 KiB

Open AccessArticle

OPTYRE—Real Time Estimation of Rolling Resistance for Intelligent Tyres

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Sensors 2019, 19(23), 5119; https://doi.org/10.3390/s19235119 - 22 Nov 2019

Cited by 7 | Viewed by 2653

Abstract

The study of the rolling tyre is a problem framed in the general context of nonlinear elasticity. The dynamics of the related phenomena is still an open topic, even though few examples and models of tyres can be found in the technical literature. [...] Read more.

The study of the rolling tyre is a problem framed in the general context of nonlinear elasticity. The dynamics of the related phenomena is still an open topic, even though few examples and models of tyres can be found in the technical literature. The interest in the dissipation effects associated with the rolling motion is justified by their importance in fuel-saving and in the context of an eco-friendly design. However, a general lack of knowledge characterizes the phenomenon, since not even direct experience on the rolling tyre can reveal the insights of the correlated different dissipation effects, as the friction between the rubber and the road, the contact kinematics and dynamics, the tyre hysteretic behaviour and the grip. A new technology, based on fibre Bragg grating strain sensors and conceived within the OPTYRE project, is illustrated for the specific investigation of the tyre dissipation related phenomena. The remarkable power of this wireless optical system stands in the chance of directly accessing the behaviour of the inner tyre in terms of stresses when a real-condition-rolling is experimentally observed. The ad hoc developed tyre model has allowed the identification of the instant grip conditions, of the area of the contact patch and allows the estimation of the instant dissipated power, which is the focus of this paper. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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9 pages, 2562 KiB

Open AccessArticle

Magnetic Field Sensor Based on a Tri-Microfiber Coupler Ring in Magnetic Fluid and a Fiber Bragg Grating

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Sensors 2019, 19(23), 5100; https://doi.org/10.3390/s19235100 - 21 Nov 2019

Cited by 19 | Viewed by 2691

Abstract

In this paper we propose and investigate a novel magnetic field sensor based on a Tri-microfiber coupler combined with magnetic fluid and a fiber Bragg grating (FBG) in a ring. A sensitivity of 1306 pm/mT was experimentally demonstrated in the range of magnetic [...] Read more.

In this paper we propose and investigate a novel magnetic field sensor based on a Tri-microfiber coupler combined with magnetic fluid and a fiber Bragg grating (FBG) in a ring. A sensitivity of 1306 pm/mT was experimentally demonstrated in the range of magnetic fields from 0 to 15 mT. The reflection peak in the output spectrum associated with the FBG serves as a reference point allowing to avoid ambiguity in determining the spectral shift induced by the magnetic field. Due to its high sensitivity at low magnetic fields, the proposed structure could be of high interest in low field biosensing applications that involve a magnetic field, such as magnetic manipulation or separation of biomolecules. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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8 pages, 2890 KiB

Open AccessArticle

Combination of an Axicon Fiber Tip and a Camera Device into a Sensitive Refractive Index Sensor

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Yi-Hsin Tai

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Po-Cheng Tsai

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Ya-Lun Ho

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Jean-Jacques Delaunay

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Pei-Kuen Wei

Sensors 2019, 19(22), 4911; https://doi.org/10.3390/s19224911 - 11 Nov 2019

Cited by 4 | Viewed by 2671

Abstract

An axicon fiber tip combined with a camera device is developed to sensitively detect refractive indexes in solutions. The transparent axicon tips were made by etching optical fibers through a wet end-etching method at room temperature. When the axicon fiber tip was immersed [...] Read more.

An axicon fiber tip combined with a camera device is developed to sensitively detect refractive indexes in solutions. The transparent axicon tips were made by etching optical fibers through a wet end-etching method at room temperature. When the axicon fiber tip was immersed in various refractive index media, the angular spectrum of the emitted light from the axicon fiber tip was changed. Using a low numerical aperture lens to collect the directly transmitted light, a high intensity sensitivity was achieved when the tip cone angle was about 35 to 40 degrees. We combined the axicon fiber tip with a laser diode and a smartphone into a portable refractometer. The front camera of the smartphone was used to collect the light emitted from the axicon fiber tip. By analyzing the selected area of the captured images, the refractive index can be distinguished for various solutions. The refractive index sensitivity was up to 56,000%/RIU, and the detection limit was 1.79 × 10⁻⁵ RIU. By measuring the refractive index change via the axicon fiber tip, the concentration of different mediums can be sensitively detected. The detection limits of the measurement for sucrose solutions, saline solutions, and diluted wine were 8.86 × 10⁻³ °Bx, 0.12‰, and 0.35%, respectively. Full article

(This article belongs to the Special Issue Optical Fiber Sensors and Photonic Devices)

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