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Feature Papers in Optical Sensors 2025

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

Deadline for manuscript submissions: 31 December 2025 | Viewed by 3662

Special Issue Editors

Prof. Dr. Yuliya Semenova

E-Mail Website
Guest Editor
School of Electrical and Electronic Engineering, Photonics Research Centre, Technological University Dublin, Grangegorman, D07 ADY7 Dublin, Ireland
Interests: optical sensing; whispering gallery mode effects in microfibre based resonators for chemical and bio-sensing; smart optical sensors for engineering applications; sensing of volatile organic compounds in environmental monitoring, medical diagnostics and industrial control; optics and applications of liquid crystals in photonics
Special Issues, Collections and Topics in MDPI journals
Dr. Gabriele Bolognini

E-Mail Website
Guest Editor
Consiglio Nazionale delle Ricerche, IMM Institute, via P Gobetti 101, I-40129 Bologna, Italy
Interests: optical fiber sensors; fiber optic communications; lasers; optical amplifiers; integrated optics; photonics and optoelectronics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Optical sensors are the subject of a huge number of studies and applications. Many well-established technologies, including free-space optics, integrated photonics, and fiber optics approaches, have been developed in recent decades to fabricate and develop increasingly more efficient optical sensors for applications ranging from industrial control to monitoring the environment, as well as biomedical use and even the Internet of Things.

The purpose of this Special Issue is to publish a set of papers that typify the most insightful and influential original articles, through which our section’s EBMs are able to discuss key topics in the field, particularly review contributions that demonstrate the advancement of optical sensing technology and successfully present new and consolidated application areas. Areas of interest include the evaluation of new sensors, new sensing principles, new applications, and new technologies, as well as review papers on the state of the art of well-established technologies for sensing. Topics of interest include group IV photonic sensors, optomechanical sensors, fiber-optic sensors, silicon photonics, plasmonic sensors, metasurfaces, and other related topics.

Prof. Dr. Yuliya Semenova
Dr. Gabriele Bolognini
Guest Editors

Manuscript Submission Information

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

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

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

Keywords

  • photonic sensors
  • optomechanical sensors
  • fiber-optic sensors
  • silicon photonics
  • plasmonic sensors

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Published Papers (7 papers)

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Research

11 pages, 1586 KiB  
Article
Quantification of Sensitization in Aluminum–Magnesium Alloys Through Frequency-Dependent Ultrasonic Attenuation
by Songwei Wang and Haiying Huang
Sensors 2025, 25(13), 3983; https://doi.org/10.3390/s25133983 - 26 Jun 2025
Viewed by 89
Abstract
Aluminum–Magnesium (Al–Mg) alloys undergo sensitization, i.e., the precipitations of β-phase (Al2Mg3) at the grain boundaries, when exposed to elevated temperature. This microstructural change increases the susceptibility of Al–Mg alloys to intergranular corrosion, exfoliation, and stress corrosion cracking. This study [...] Read more.
Aluminum–Magnesium (Al–Mg) alloys undergo sensitization, i.e., the precipitations of β-phase (Al2Mg3) at the grain boundaries, when exposed to elevated temperature. This microstructural change increases the susceptibility of Al–Mg alloys to intergranular corrosion, exfoliation, and stress corrosion cracking. This study introduces a time-frequency analysis (TFA) technique to determine the frequency-dependent ultrasonic attenuation parameter and correlate the frequency-attenuation slope to the Degree of Sensitization (DoS) developed in heat-treated Al–Mg alloy samples. Broadband pitch-catch signal was generated using a laser ultrasonic testing (LUT) system, from which the narrowband pitch-catch signal at different frequencies can be digitally generated. The attenuation parameters of sensitized Al–Mg samples were determined from these narrowband pitch-catch signals using the primary pulse-first echo (PP-FE) method. By identifying the frequency range within which the attenuation parameter is linearly proportional to the frequency, the slopes of the frequency-attenuation relationship were determined and correlated with the DoS values of the sample plates. The experimental results validate that the frequency-attenuation slope has a higher sensitivity and lower scattering as compared to other conventional ultrasonic attenuation measurement techniques. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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14 pages, 3702 KiB  
Article
A High-Sensitivity U-Shaped Optical Fiber SPR Sensor Based on ITO Coating
by Chuhan Ye, Zhibo Li, Wenhao Kang and Lei Hou
Sensors 2025, 25(13), 3911; https://doi.org/10.3390/s25133911 - 23 Jun 2025
Viewed by 169
Abstract
This paper proposes a high-sensitivity U-shaped optical fiber sensor based on indium tin oxide (ITO) for surface plasmon resonance (SPR) sensing. Finite element simulations reveal that introducing ITO enhances the surface electric field strength by 1.15× compared to conventional designs, directly boosting sensitivity. [...] Read more.
This paper proposes a high-sensitivity U-shaped optical fiber sensor based on indium tin oxide (ITO) for surface plasmon resonance (SPR) sensing. Finite element simulations reveal that introducing ITO enhances the surface electric field strength by 1.15× compared to conventional designs, directly boosting sensitivity. The U-shaped structure optimizes evanescent wave–metal film interaction, further improving performance. In an external refractive index (RI) range of 1.334–1.374 RIU, the sensor achieves a sensitivity of 4333 nm/RIU (1.85× higher than traditional fiber sensors) and a figure of merit (FOM) of 21.7 RIU−1 (1.68× improvement). Repeatability tests show a low relative standard deviation (RSD) of 0.4236% for RI measurements, with a maximum error of 0.00018 RIU, confirming excellent stability. The ITO coating’s strong adhesion ensures long-term reliability. With its simple structure, ease of fabrication, and superior sensitivity/FOM, this SPR sensor is well-suited for high-precision biochemical detection in intelligent sensing systems. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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16 pages, 8177 KiB  
Article
Study and Characterization of Silicon Nitride Optical Waveguide Coupling with a Quartz Tuning Fork for the Development of Integrated Sensing Platforms
by Luigi Melchiorre, Ajmal Thottoli, Artem S. Vorobev, Giansergio Menduni, Angelo Sampaolo, Giovanni Magno, Liam O’Faolain and Vincenzo Spagnolo
Sensors 2025, 25(12), 3663; https://doi.org/10.3390/s25123663 - 11 Jun 2025
Viewed by 455
Abstract
This work demonstrates an ultra-compact optical gas-sensing system, consisting of a pigtailed laser diode emitting at 1392.5 nm for water vapor (H2O) detection, a silicon nitride (Si3N4) optical waveguide to guide the laser light, and a custom-designed, [...] Read more.
This work demonstrates an ultra-compact optical gas-sensing system, consisting of a pigtailed laser diode emitting at 1392.5 nm for water vapor (H2O) detection, a silicon nitride (Si3N4) optical waveguide to guide the laser light, and a custom-designed, low-frequency, and T-shaped Quartz Tuning Fork (QTF) as the sensitive element. The system employs both Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) and Light-Induced Thermoelastic Spectroscopy (LITES) techniques for trace gas sensing. A 3.8 mm-wide, S-shaped waveguide path was designed to prevent scattered laser light from directly illuminating the QTF. Both QEPAS and LITES demonstrated comparably low signal-to-noise ratios (SNRs), ranging from 1.6 to 3.2 for a 1.6% indoor H2O concentration, primarily owing to the reduced optical power (~300 μW) delivered to the QTF excitation point. These results demonstrate the feasibility of integrating photonic devices and piezoelectric components into portable gas-sensing systems for challenging environments. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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13 pages, 2773 KiB  
Article
Effect of Rare-Earth Co-Doping on the Trap Level Concentrations in Silica Glasses: Experimental and Theoretical Study of the Light Emission Under X-Rays for Dosimetry Applications
by Ismail Zghari, Hicham El Hamzaoui, Adriana Morana, Youcef Ouerdane, Bruno Capoen, Sarah Garzandat, Sylvain Girard, Aziz Boukenter, Franck Mady, Mourad Benabdesselam, Gilles Mélin and Mohamed Bouazaoui
Sensors 2025, 25(10), 3005; https://doi.org/10.3390/s25103005 - 9 May 2025
Viewed by 345
Abstract
In this paper, an experimental and theoretical study was undertaken to assess the impact of rare-earth co-doping of silica glasses on the light emission under X-rays. To this aim, radioluminescence (RL), phosphorescence (PP), and thermoluminescence (TL) signals of Ce3+/Gd3+ co-doped [...] Read more.
In this paper, an experimental and theoretical study was undertaken to assess the impact of rare-earth co-doping of silica glasses on the light emission under X-rays. To this aim, radioluminescence (RL), phosphorescence (PP), and thermoluminescence (TL) signals of Ce3+/Gd3+ co-doped silica glasses have been successively measured and combined at different dose rates and irradiation temperatures. The RL response of the weakly co-doped sample was found to be temperature-independent between 273 K and 353 K. This result suggests that, based on this RL response, it is possible to design ionizing radiation sensors independent of the irradiation temperature in the corresponding range. Moreover, a model that considers the electron–hole pair generation, the charge carrier trapping–detrapping, and the electron–hole recombination in the localized and delocalized bands has been developed to reproduce these optical signals. The theoretical model also explains the temperature independence of the RL response between 273 K and 353 K for the weakly co-doped sample and, therefore, the operating principle of an X-ray sensor independent of the irradiation temperature. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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21 pages, 4964 KiB  
Article
Uncertainty Analysis of Fiber Optic Shape Sensing Under Core Failure
by Francesco Falcetelli, Leonardo Rossi, Raffaella Di Sante and Gabriele Bolognini
Sensors 2025, 25(8), 2353; https://doi.org/10.3390/s25082353 - 8 Apr 2025
Viewed by 421
Abstract
Shape sensing with optical fiber sensors is an emerging technology with broad applications across various fields. This study evaluates the metrological performance of shape sensing cables in the presence of fiber core failures, a critical issue in scenarios where cable replacement is impractical [...] Read more.
Shape sensing with optical fiber sensors is an emerging technology with broad applications across various fields. This study evaluates the metrological performance of shape sensing cables in the presence of fiber core failures, a critical issue in scenarios where cable replacement is impractical due to technological and economic constraints. The impact of core failure is quantified by comparing the uncertainty in key parameters, such as curvature and bending angle, between pristine and damaged cables through Monte Carlo simulations. Results indicate that while core failure degrades performance, shape reconstruction remains achievable. However, the reconstruction becomes sensitive to bending direction due to the loss of core symmetry. Additionally, simulations of how measurement noise propagates into uncertainty in the 3D shape reconstruction are carried out. Analysis of specific shapes, including a circle and a right-handed helix, shows that increasing the number of sensing cores significantly mitigates the adverse effects of core failure. The most notable improvement occurs when the number of cores is increased from four to five. These findings show how shape reconstruction is still possible even in the presence of core damage, and how this changes the behavior of the sensing process. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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13 pages, 3289 KiB  
Article
Research on High-Responsivity Si/Ge-APD in Visible–Near-Infrared Wide Spectrum with Light-Absorption-Enhanced Nanostructure
by Guangtong Guo, Weishuai Chen, Kaifeng Zheng, Jinguang Lv, Yupeng Chen, Baixuan Zhao, Yingze Zhao, Yuxin Qin, Xuefei Wang, Dan Gao, Jingqiu Liang and Weibiao Wang
Sensors 2025, 25(4), 1167; https://doi.org/10.3390/s25041167 - 14 Feb 2025
Viewed by 724
Abstract
Photodetectors with broad spectral response and high responsivity demonstrate significant potential in optoelectronic applications. This study proposes a Si/Ge avalanche photodiode featuring nanostructures that enhance light absorption. By optimizing the device epitaxial structure and these nanostructures, a wide spectral responsivity from 0.4 to [...] Read more.
Photodetectors with broad spectral response and high responsivity demonstrate significant potential in optoelectronic applications. This study proposes a Si/Ge avalanche photodiode featuring nanostructures that enhance light absorption. By optimizing the device epitaxial structure and these nanostructures, a wide spectral responsivity from 0.4 to 1.6 μm is achieved. The results demonstrate that introducing surface photon-trapping nanoholes and SiO2 reflective grating nanostructures increases the average light absorptivity from 0.64 to 0.84 in the 0.4–1.1 μm range and from 0.31 to 0.56 in the 1.1–1.6 μm range. At an applied bias of 0.95 Vbr-apd, the responsivity reaches 17.24 A/W at 1.31 μm and 17.6 A/W at 1.55 μm. This research provides theoretical insights for designing high-responsivity photodetectors in the visible–near-infrared broadband spectrum. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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16 pages, 4009 KiB  
Article
Curved Fabry-Pérot Ultrasound Detectors: Optical and Mechanical Analysis
by Barbara Rossi, Maria Alessandra Cutolo, Martino Giaquinto, Andrea Cusano and Giovanni Breglio
Sensors 2025, 25(4), 1014; https://doi.org/10.3390/s25041014 - 8 Feb 2025
Cited by 1 | Viewed by 845
Abstract
Optical fiber-based acoustic detectors for ultrasound imaging in medical field feature plano-concave Fabry–Perot cavities integrated on fiber tips, realized via dip-coating. This technique imposes constraints on sensor geometry, potentially limiting performance. Lab-on-Fiber technology enables complex three-dimensional structures with precise control over geometric parameters, [...] Read more.
Optical fiber-based acoustic detectors for ultrasound imaging in medical field feature plano-concave Fabry–Perot cavities integrated on fiber tips, realized via dip-coating. This technique imposes constraints on sensor geometry, potentially limiting performance. Lab-on-Fiber technology enables complex three-dimensional structures with precise control over geometric parameters, such as the curvature radius. A careful investigation of the optical and mechanical aspects involved in the sensors’ performances is crucial for determining the design rules of such probes. In this study, we numerically analyzed the impact of curvature on the optical and acoustic properties of a plano-concave cavity using the Finite Element Method. Performance metrics, including sensitivity, bandwidth, and directivity, were compared to planar Fabry–Perot configurations. The results suggest that introducing curvature significantly enhances sensitivity by improving light confinement, especially for cavity thicknesses exceeding half the Rayleigh zone (∼45 μm), reaching an enhancement of 2.5 a L = 60 μm compared to planar designs. The curved structure maintains high spectral quality (FOM) despite 2% fabrication perturbations. A mechanical analysis confirms no disadvantages in acoustic response and bandwidth (∼40 MHz). These findings establish curved plano-concave structures as robust and reliable for high-sensitivity polymeric lab-on-fiber ultrasound detectors, offering improved performance and fabrication tolerance for MHz-scale bandwidth applications. Full article
(This article belongs to the Special Issue Feature Papers in Optical Sensors 2025)
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