Special Issue "Optical Sensing"

A special issue of Photonics (ISSN 2304-6732). This special issue belongs to the section "Lasers, Light Sources and Sensors".

Deadline for manuscript submissions: 10 February 2022.

Special Issue Editors

Dr. Garoli Denis
E-Mail Website
Guest Editor
Faculty of Science and Technology Free University of Bozen, Piazza Università 5, 39100 Bolzano, Italy
Interests: single molecule spectroscopy; nanopores; 2D materials; plasmonics; nanofabrication
Dr. Cheng Jiang
E-Mail Website
Guest Editor
Tofaris Group, Nuffield Department of Clinical Neurosciences (NDCN), West Wing Level 6, JR hospital University of Oxford, Oxford, UK
Interests: exosomes; PoC device; high-throughput profiling; biomarker discovery
Dr. Jian-An Huang
E-Mail Website
Guest Editor
Faculty of Medicine, University of Oulu, Oulu, Finland
Interests: plasmonics; nanophotonics and nano-optics; optofluidics; surface-enhanced spectroscopies; biophysics; optical biosensing; single-cell analysis; single-molecule Sequencing

Special Issue Information

Dear Colleagues,

Optical sensing plays a vital role in the large family of sensing applications, and has witnessed rapid progress in diverse aspects, ranging, for example, from fundamental theory/simulation studies to practical sensing applications, from in vitro to in vivo, from bulky optical solid-state devices to microscopic optical molecular probes/reporters, etc.

Aiming to bring researchers in the optical sensing field together to display their excellent works, this Special Issue on optical sensing offers a platform for you to showcase your works, providing an overview of the recent developments and strategies related to optical sensing covering topics including (but not limited to) those stated above; both research articles and reviews are welcome.

In optical sensing applications, either the manipulation of optical transducers or the rational design of optical molecular probes are within the scope, including wide ranges of optical sensory device types, such as optical electrochemical (OEC), chemiluminescence, fluorescence, colorimetric, FRET, BRET, SPR, SERS, etc.

Dr. Garoli Denis
Dr. Cheng Jiang
Dr. Jian-An Huang
Guest Editors

Manuscript Submission Information

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

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • optical sensing
  • optical molecular probe
  • solid-state device

Published Papers (14 papers)

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Research

Article
Fast Measurement of Brillouin Frequency Shift in Optical Fiber Based on a Novel Feedforward Neural Network
Photonics 2021, 8(11), 474; https://doi.org/10.3390/photonics8110474 - 25 Oct 2021
Viewed by 405
Abstract
Brillouin scattering-based distributed optical fiber sensors have been successfully employed in various applications in recent decades, because of benefits such as small size, light weight, electromagnetic immunity, and continuous monitoring of temperature and strain. However, the data processing requirements for the Brillouin Gain [...] Read more.
Brillouin scattering-based distributed optical fiber sensors have been successfully employed in various applications in recent decades, because of benefits such as small size, light weight, electromagnetic immunity, and continuous monitoring of temperature and strain. However, the data processing requirements for the Brillouin Gain Spectrum (BGS) restrict further improvement of monitoring performance and limit the application of real-time measurements. Studies using Feedforward Neural Network (FNN) to measure Brillouin Frequency Shift (BFS) have been performed in recent years to validate the possibility of improving measurement performance. In this work, a novel FNN that is 3 times faster than previous FNNs is proposed to improve BFS measurement performance. More specifically, after the original Brillouin Gain Spectrum (BGS) is preprocessed by Principal Component Analysis (PCA), the data are fed into the Feedforward Neural Network (FNN) to predict BFS. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Accurate 3D Shape Reconstruction from Single Structured-Light Image via Fringe-to-Fringe Network
Photonics 2021, 8(11), 459; https://doi.org/10.3390/photonics8110459 - 20 Oct 2021
Viewed by 371
Abstract
Accurate three-dimensional (3D) shape reconstruction of objects from a single image is a challenging task, yet it is highly demanded by numerous applications. This paper presents a novel 3D shape reconstruction technique integrating a high-accuracy structured-light method with a deep neural network learning [...] Read more.
Accurate three-dimensional (3D) shape reconstruction of objects from a single image is a challenging task, yet it is highly demanded by numerous applications. This paper presents a novel 3D shape reconstruction technique integrating a high-accuracy structured-light method with a deep neural network learning scheme. The proposed approach employs a convolutional neural network (CNN) to transform a color structured-light fringe image into multiple triple-frequency phase-shifted grayscale fringe images, from which the 3D shape can be accurately reconstructed. The robustness of the proposed technique is verified, and it can be a promising 3D imaging tool in future scientific and industrial applications. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
A Preliminary Assessment of an FBG-Based Hard Landing Monitoring System
Photonics 2021, 8(10), 450; https://doi.org/10.3390/photonics8100450 - 17 Oct 2021
Cited by 1 | Viewed by 287
Abstract
In aeronautics, hard landing is a critical condition as the aircraft approaches the runway with a vertical velocity that exceeds 2 m/s. Beyond that level, the energy that should be then absorbed by the whole structure could cause severe damage to the landing [...] Read more.
In aeronautics, hard landing is a critical condition as the aircraft approaches the runway with a vertical velocity that exceeds 2 m/s. Beyond that level, the energy that should be then absorbed by the whole structure could cause severe damage to the landing gear and the whole structural system. This document reports on the set-up, execution and results of a preparatory test campaign performed on a small landing gear (LG) demonstrator instrumented with a fibre-optic sensor system. In detail, a leaf spring landing gear was released from a drop tower to detect information about the strain state and the related acceleration history of some specific components during the impact. The objective of the present research is the development of a method for assessing whether hard landing is experienced, and to what extent. Deformation measurements through an integrated Fibre-Bragg Grating (FBG) network allowed retrieving impact velocity by a devoted, original algorithm. The proposed preliminary methodology is the base for assessing a more complex procedure to correlate structural response to the energy entering the structure during the touchdown event. Full article
(This article belongs to the Special Issue Optical Sensing)
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Communication
Highly Sensitive Biosensor Based on Partially Immobilized Silver Nanopillars in the Terahertz Band
Photonics 2021, 8(10), 438; https://doi.org/10.3390/photonics8100438 - 13 Oct 2021
Viewed by 269
Abstract
In this paper, a highly sensitive biosensor based on partially immobilized silver nanopillars is proposed. The working frequency of this sensor is in the terahertz band, and the range of the detected refractive index is 1.33 to 1.38. We set air holes of [...] Read more.
In this paper, a highly sensitive biosensor based on partially immobilized silver nanopillars is proposed. The working frequency of this sensor is in the terahertz band, and the range of the detected refractive index is 1.33 to 1.38. We set air holes of two different sizes on the cross-section of the optical fiber and arranged them into a hexagon. In order to improve the sensitivity, silver nanopillars were immobilized on part of the surface of the fiber cladding. The method for detecting the change of refractive index of the bio-analyte was based on local surface plasmon resonance properties of noble metal. The research recorded valuable data about the values of loss peak and full width at half maximum as well as resonance frequency shift under different setting conditions. The data present the biosensor’s final sensitivity as 1.749 THz/RIU. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Dual-Modality Imaging Microfluidic Cytometer for Onsite Detection of Phytoplankton
Photonics 2021, 8(10), 435; https://doi.org/10.3390/photonics8100435 - 12 Oct 2021
Viewed by 301
Abstract
Phytoplankton monitoring is essential for better understanding and mitigation of phytoplankton bloom formation. We present a microfluidic cytometer with two imaging modalities for onsite detection and identification of phytoplankton: a lensless imaging mode for morphological features, and a fluorescence imaging mode for autofluorescence [...] Read more.
Phytoplankton monitoring is essential for better understanding and mitigation of phytoplankton bloom formation. We present a microfluidic cytometer with two imaging modalities for onsite detection and identification of phytoplankton: a lensless imaging mode for morphological features, and a fluorescence imaging mode for autofluorescence signal of phytoplankton. Both imaging modes are integrated in a microfluidic device with a field of view (FoV) of 3.7 mm × 2.4 mm and a depth of field (DoF) of 0.8 mm. The particles in the water flow channel can be detected and classified with automated image processing algorithms and machine learning models using their morphology and fluorescence features. The performance of the device was demonstrated by measuring Chlamydomonas, Euglena, and non-fluorescent beads in both separate and mixed flow samples. The recall rates for Chlamydomonas and Euglena ware 93.6% and 94.4%. The dual-modality imaging approach enabled observing both morphology and fluorescence features with a large DoF and FoV which contribute to high-throughput analysis. Moreover, this imaging flow cytometer platform is portable, low-cost, and shows potential in the onsite phytoplankton monitoring. Full article
(This article belongs to the Special Issue Optical Sensing)
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Communication
Optical Detection of VOC Vapors Using Nb2O5 Bragg Stack in Transmission Mode
Photonics 2021, 8(9), 399; https://doi.org/10.3390/photonics8090399 - 18 Sep 2021
Viewed by 306
Abstract
In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optical sensors. All-niobia Bragg stacks were deposited by spin-coating of sol-gel Nb2O5 thin films alternated with mesoporous layers after proper design through optimization of [...] Read more.
In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optical sensors. All-niobia Bragg stacks were deposited by spin-coating of sol-gel Nb2O5 thin films alternated with mesoporous layers after proper design through optimization of operating wavelength and number of layers in the stack. Mesoporous Nb2O5 films with different morphology and identical structure were obtained using organic templates (Pluronics PE6200 and PE6800) and subsequent annealing. Transmittance measurements were performed as a detection method that offers technological simplicity and accuracy. It was demonstrated that stacks including PE6200 templated films exhibit higher sensitivity than stacks templated with PE6800. It was assumed and verified by computer-aided modelling of experimental data that mesoporous films prepared with addition of PE6200, although less porous, were more stable compared to those templated with PE6800, and did not collapse during the thermal treatment of the stacks. Furthermore, the reproducibility of optical response was studied by sorption and desorption cycles of acetone vapors. The suitability of all-niobia Bragg stacks for optical sensing of VOCs was discussed. Full article
(This article belongs to the Special Issue Optical Sensing)
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Communication
Ultra-Sensitive Intensity Modulated Strain Sensor by Tapered Thin-Core Fiber Based Modal Interferometer
Photonics 2021, 8(9), 372; https://doi.org/10.3390/photonics8090372 - 03 Sep 2021
Viewed by 629
Abstract
In this paper, to enhance practicality, a novel tapered thin-core fiber (t-TCF) based modal interferometer is proposed and demonstrated experimentally. The light field distribution of t-TCF structure is investigated by a beam propagation method, and the quantitative relationship is gained [...] Read more.
In this paper, to enhance practicality, a novel tapered thin-core fiber (t-TCF) based modal interferometer is proposed and demonstrated experimentally. The light field distribution of t-TCF structure is investigated by a beam propagation method, and the quantitative relationship is gained between light intensity loss and waist diameter. Under ~30 μm waist diameter, multiple t-TCF based sensor heads are fabricated by arc-discharged splicing and taper techniques, and comprehensive tests are performed with respects to axial strain and temperature. The experimental results show that, with near-zero wavelength shift, obvious intensity strain response is exhibited and negative-proportional to the reduced length of TCF. Thus, the maximum sensitivity reaches 0.119 dB/με when the TCF length is equal to 15 mm, and a sub-micro-strain detection resolution (about 0.084 με) is obtained. Besides, owing to the flat red-shifted temperature response, the calculated cross-sensitivity of our sensor is compressed within 0.32 με/°C, which is promising for high precision strain related engineering applications. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Magnetic Field Sensing Characteristics Based on Optical Microfiber Coupler Interferometer and Magnetic Fluid
Photonics 2021, 8(9), 364; https://doi.org/10.3390/photonics8090364 - 30 Aug 2021
Viewed by 427
Abstract
In this paper, a novel and compact magnetic field sensor based on the combination of an optical microfiber coupler interferometer (OMCI) and magnetic fluid (MF) is proposed. The sensor is made up of an OMCI cover with polydimethylsiloxane (PDMS) and MF, and it [...] Read more.
In this paper, a novel and compact magnetic field sensor based on the combination of an optical microfiber coupler interferometer (OMCI) and magnetic fluid (MF) is proposed. The sensor is made up of an OMCI cover with polydimethylsiloxane (PDMS) and MF, and it uses MF as a material for adjusting the magnetic refractive index and magnetic field response. The sensing characteristics of the sensor are analyzed, and the experimental test is carried out. Under the condition of the same OMC waist length, the sensor sensitivity increases with the decrease of the OMC waist radius. The sensitivity of 54.71 and 48.21 pm/Oe was obtained when the OMC waist radius was set at 3.5 and 4 μm, respectively. In addition, we also tested the sensing response time and vector response characteristics of the sensor. At the same time, we discuss the demodulation idea about the cross-sensitivity of the magnetic field and temperature. The sensor has the advantages of high sensitivity, low cost, small size, optimized performance, and convenient integration. It has huge application potential in the fields of navigation and industrial intelligent manufacturing. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Theoretical Considerations of Photonic Crystal Fiber with All Uniform-Sized Air Holes for Liquid Sensing
Photonics 2021, 8(7), 249; https://doi.org/10.3390/photonics8070249 - 30 Jun 2021
Cited by 2 | Viewed by 455
Abstract
A novel liquid-infiltrated photonic crystal fiber model applicable in liquid sensing for different test liquids—water, ethanol and benzene—has been proposed. One core hole and three air hole rings have been designed and a full vector finite element method has been used for numerical [...] Read more.
A novel liquid-infiltrated photonic crystal fiber model applicable in liquid sensing for different test liquids—water, ethanol and benzene—has been proposed. One core hole and three air hole rings have been designed and a full vector finite element method has been used for numerical investigation to give the best results in terms of relative sensitivity, confinement loss, power fraction, dispersion, effective area, nonlinear coefficient, numerical aperture and V-Parameter. Specially, the assessed relative sensitivities of the proposed fiber with water, ethanol and benzene are 94.26%, 95.82% and 99.58%, respectively, and low confinement losses of 1.52 × 10−11 dB/m with water, 1.21 × 10−12 dB/m with ethanol and 6.01 × 10−16 dB/m with benzene, at 1.0 μm operating wavelength. This novel PCF design is considered simple and can be easily fabricated for practical use, and the assessed waveguide properties has determined the potential applicability in real liquid sensing applications. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Development of a Temperature-Controlled Optical Planar Waveguide Sensor with Lossy Mode Resonance for Refractive Index Measurement
Photonics 2021, 8(6), 199; https://doi.org/10.3390/photonics8060199 - 04 Jun 2021
Viewed by 1209
Abstract
The generation of lossy mode resonances (LMR) with a metallic oxide film deposited on an optical fiber has attracted the attention of many applications. However, an LMR-based optical fiber sensor is frangible, and therefore it does not allow control of the temperature and [...] Read more.
The generation of lossy mode resonances (LMR) with a metallic oxide film deposited on an optical fiber has attracted the attention of many applications. However, an LMR-based optical fiber sensor is frangible, and therefore it does not allow control of the temperature and is not suited to mass production. This paper aims to develop a temperature-controlled lossy mode resonance (TC-LMR) sensor on an optical planar waveguide with an active temperature control function in which an ITO film is not only used as the LMR resonance but also to provide the heating function to achieve the benefits of compact size and active temperature control. A simple flat model about the heat transfer mechanism is proposed to determine the heating time constant for the applied voltages. The TC-LMR sensor is evaluated experimentally for refractive index measurement using a glycerol solution. The heating temperature functions relative to the controlled voltages for water and glycerol are obtained to verify the performance of the TC-LMR sensor. The TC-LMR sensor is a valuable sensing device that can be used in clinical testing and point of care for programming heating with precise temperature control. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Computational Method for Wavefront Sensing Based on Transport-of-Intensity Equation
Photonics 2021, 8(6), 177; https://doi.org/10.3390/photonics8060177 - 22 May 2021
Viewed by 773
Abstract
Recently the transport-of-intensity equation as a phase imaging method turned out as an effective microscopy method that does not require the use of high-resolution optical systems and a priori information about the object. In this paper we propose a mathematical model that adapts [...] Read more.
Recently the transport-of-intensity equation as a phase imaging method turned out as an effective microscopy method that does not require the use of high-resolution optical systems and a priori information about the object. In this paper we propose a mathematical model that adapts the transport-of-intensity equation for the purpose of wavefront sensing of the given light wave. The analysis of the influence of the longitudinal displacement z and the step between intensity distributions measurements on the error in determining the wavefront radius of curvature of a spherical wave is carried out. The proposed method is compared with the traditional Shack–Hartmann method and the method based on computer-generated Fourier holograms. Numerical simulation showed that the proposed method allows measurement of the wavefront radius of curvature with radius of 40 mm and with accuracy of ~200 μm. Full article
(This article belongs to the Special Issue Optical Sensing)
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Graphical abstract

Article
Generalized Resonance Sensor Based on Fiber Bragg Grating
Photonics 2021, 8(5), 156; https://doi.org/10.3390/photonics8050156 - 06 May 2021
Cited by 1 | Viewed by 682
Abstract
In response to the difficulty of weak detection of early bearing damage, resonance demodulation technology and the principle of fiber Bragg grating sensing strain were combined to design a fiber Bragg grating generalized resonance sensor, which can extract the weak pulse signal of [...] Read more.
In response to the difficulty of weak detection of early bearing damage, resonance demodulation technology and the principle of fiber Bragg grating sensing strain were combined to design a fiber Bragg grating generalized resonance sensor, which can extract the weak pulse signal of weak detection of early bearing’s early damage from rolling bearing. First, a principle of resonance dynamics of second-order mechanical systems based on fiber Bragg grating and generalized resonance principles is proposed. Second, the basic structure of the sensor is designed. Then, ANSYS finite element simulation is used to analyze the natural frequency of the sensor. Finally, the natural frequency value of the sensor was obtained through experiments. The experimental results of proof-of-principle show that the experimental results are consistent with the theoretical predictions. The theoretical model is accurate, which verifies the feasibility of the sensor. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Study on the Nanosensor Based on a MIM Waveguide with a Stub Coupled with a Horizontal B-Type Cavity
Photonics 2021, 8(4), 125; https://doi.org/10.3390/photonics8040125 - 16 Apr 2021
Cited by 2 | Viewed by 574
Abstract
Due to their compact size and high sensitivity, plasmonic sensors have become a hot topic in the sensing field. A nanosensor structure, comprising the metal–insulator–metal (MIM) waveguide with a stub and a horizontal B-Type cavity, is designed as a refractive index sensor. The [...] Read more.
Due to their compact size and high sensitivity, plasmonic sensors have become a hot topic in the sensing field. A nanosensor structure, comprising the metal–insulator–metal (MIM) waveguide with a stub and a horizontal B-Type cavity, is designed as a refractive index sensor. The spectral characteristics of proposed structure are analyzed via the finite element method (FEM). The results show that there is a sharp Fano resonance profile, which is excited by a coupling between the MIM waveguide and the horizontal B-Type cavity. The normalized HZ field is affected by the difference value between the outer radii R1 and R2 of the semi-circle of the horizontal B-Type cavity greatly. The influence of every element of the whole system on sensing properties is discussed in depth. The sensitivity of the proposed structure can obtain 1548 nm/RIU (refractive index unit) with a figure of merit of 59. The proposed structure has potential in nanophotonic sensing applications. Full article
(This article belongs to the Special Issue Optical Sensing)
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Article
Design and Simulation of Photonic Crystal Fiber for Liquid Sensing
Photonics 2021, 8(1), 16; https://doi.org/10.3390/photonics8010016 - 12 Jan 2021
Cited by 4 | Viewed by 942
Abstract
A simple hexagonal lattice photonic crystal fiber model with liquid-infiltrated core for different liquids: water, ethanol and benzene, has been proposed. In the proposed structure, three air hole rings are present in the cladding and three equal sized air holes are present in [...] Read more.
A simple hexagonal lattice photonic crystal fiber model with liquid-infiltrated core for different liquids: water, ethanol and benzene, has been proposed. In the proposed structure, three air hole rings are present in the cladding and three equal sized air holes are present in the core. Numerical investigation of the proposed fiber has been performed using full vector finite element method with anisotropic perfectly match layers, to show that the proposed simple structure exhibits high relative sensitivity, high power fraction, relatively high birefringence, low chromatic dispersion, low confinement loss, small effective area, and high nonlinear coefficient. All these properties have been numerically investigated at a wider wavelength regime 0.6–1.8 μm within mostly the IR region. Relative sensitivities of water, ethanol and benzene are obtained at 62.60%, 65.34% and 74.50%, respectively, and the nonlinear coefficients are 69.4 W−1 km−1 for water, 73.8 W−1 km−1 for ethanol and 95.4 W−1 km−1 for benzene, at 1.3 µm operating wavelength. The simple structure can be easily fabricated for practical use, and assessment of its multiple waveguide properties has justified its usage in real liquid detection. Full article
(This article belongs to the Special Issue Optical Sensing)
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