Contents
2025
Volume: 15 Issue 2
15 Article(s)
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Two-Dimensional Reconstructed Image of a Subsurface Structure Using Continuous Scanned Photothermal Imaging
KIM Moojoong, and KIM Hyunjung
This study presents the two-dimensional (2D) image of a subsurface structure reconstructed using an imaging method based on the photothermal effect. The photothermal imaging method is based on the deflection method using two lasers: pump and probe lasers. A continuous scanning technique is proposed for 2D (x- and y-dirThis study presents the two-dimensional (2D) image of a subsurface structure reconstructed using an imaging method based on the photothermal effect. The photothermal imaging method is based on the deflection method using two lasers: pump and probe lasers. A continuous scanning technique is proposed for 2D (x- and y-directions) surface scanning. The continuous scanning method is compared with the conventional point-by-point scanning technique, and a low-pass fast Fourier transform filter and a Marr-Hildreth detector are found to produce significant results. The photothermal imaging method with continuous 2D surface scanning is performed on three copper-resin double-layer samples with different subsurface structures. The subsurface structures of the copper-resin double-layer samples comprise a square block of 5×5 mm2 area and blocks shaped as the alphabet letters “T” and “F”. The letters are 3 mm wide and 10×13 mm2 in area. All three shapes are 1 mm thick and located at a depth of 0.5 mm from the surface of the copper block. The reconstructed photothermal images show an absolute error within 0.122 mm compared with the actual subsurface structure, equivalent to a 2.3% relative error..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250201 (2025)
Humidity Sensor Based on a Hollow Core Fiber Anti-Resonant Reflection Optical Waveguide
CHENG Ao, WANG Chaoqi, XU Jiadong, ZHANG Peiqing... and DAI Shixun|Show fewer author(s)
In this paper, a graphene oxide (GO) composite film-coated humidity sensor is proposed based on the hollow core fiber (HCF). A segment of the HCF is spliced between two segments of the single-mode fiber (SMF). The relative humidity (RH) sensing characteristics of the sensor are experimentally investigated by observing In this paper, a graphene oxide (GO) composite film-coated humidity sensor is proposed based on the hollow core fiber (HCF). A segment of the HCF is spliced between two segments of the single-mode fiber (SMF). The relative humidity (RH) sensing characteristics of the sensor are experimentally investigated by observing the intensity shift of resonant dips in the transmission spectrum, which shows the GO composite film-coated HCF has the good stability in the measurement of humidity. The maximum humidity sensitivity of 0.12 dB/%RH is obtained in the RH range of 30%–78%. The proposed sensor has the advantages of the simple structure, easy fabrication, good stability, and high performance, which can be applied to marine climate detection, tunnel air humidity detection, agricultural testing, and other fields..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250202 (2025)
FBG-Based UV-Curing Kinetics Analysis by Exothermic Behavior
YAN Wen, BI Zhenhua, SONG Ying, and ZHANG Xinpu
Since photo-induced polymerization of the ultra-violet (UV)-curing adhesive from a fluid state to a solid state is an exothermic process, the UV curing exothermic behavior can be regarded as a potential evaluation methodology to analyze UV-curing kinetics. Herein, a fiber Bragg grating (FBG)-based UV curing exothermic Since photo-induced polymerization of the ultra-violet (UV)-curing adhesive from a fluid state to a solid state is an exothermic process, the UV curing exothermic behavior can be regarded as a potential evaluation methodology to analyze UV-curing kinetics. Herein, a fiber Bragg grating (FBG)-based UV curing exothermic behavior monitoring is proposed to evaluate the UV-curing dynamic process and analyze a series of thermal and mechanical properties changes during curing. The exothermic behavior of the UV curing adhesive during curing and the feasibility of FBG-based curing kinetic analysis scheme are verified experimentally, full cycle cure monitoring of the UV curing adhesive can be realized by this FBG-based curing kinetic analysis scheme, and the UV-curing kinetics of four different types of the UV curing adhesive are corresponding to different exothermic behaviors. Compared with curing process evaluation based on refractive index variation, this FBG-based exothermic behavior monitoring has the ability to extract more details of the curing process, and some curing stages with negligible refractive index changes also can be distinguished. By using this proposed scheme, the UV-curing dynamic process and multiple characteristic parameters, such as curing time, time constant, transient temperature rise, and residual stress, can be evaluated, which may contribute to evaluating and analyzing UV-curing kinetics more comprehensively..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250203 (2025)
Optical Fiber Hydrogen Sensor Based on π-Phase-Shifted Grating and Sputtered Pd/Hf Composite Film
ZHANG Fan, BUCHFELLNER Fabian, HU Wenbin, AO Wenxin... and YANG Minghong|Show fewer author(s)
A novel optical fiber hydrogen sensor based on the -phase-shifted grating and partial coated Pd/Hf composite film is proposed and experimentally demonstrated in this paper. The hydrogen sensitive Pd/Hf film with the length of 4 mm is successfully deposited in the -phase-shifted grating region by the magnetron sputterinA novel optical fiber hydrogen sensor based on the π-phase-shifted grating and partial coated Pd/Hf composite film is proposed and experimentally demonstrated in this paper. The hydrogen sensitive Pd/Hf film with the length of 4 mm is successfully deposited in the π-phase-shifted grating region by the magnetron sputtering process and rotating fixture technology. Since the hydrogen sensitivity between the notch and flank wavelengths of the π-phase-shifted grating is different due to the partial coating only on the π-phase-shifted grating region, the relative shift between the notch and flank wavelengths is employed to characterize the hydrogen concentration in this paper. The hydrogen calibration results show that the sensor shows the good response and repeatability. At the temperature of 20 ℃ and the hydrogen concentration of 2%, the wavelength distance shifts of 200 nm and 500 nm Pd/Hf coatings are 12.6 pm and 33.5 pm, respectively..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250204 (2025)
Artificial Neural Networks as Digital Twins for Whispering Gallery Mode Optical Sensors in Robotics Applications
ALI Amir R., and RAMADAN Mohamed W. A.
This paper investigates the use of artificial neural networks (ANNs) as a viable digital twin or alternative to the typical whispering gallery mode (WGM) optical sensors in engineering systems, especially in dynamic environments like robotics. Because of its fragility and limited endurance, the WGM sensor which is baseThis paper investigates the use of artificial neural networks (ANNs) as a viable digital twin or alternative to the typical whispering gallery mode (WGM) optical sensors in engineering systems, especially in dynamic environments like robotics. Because of its fragility and limited endurance, the WGM sensor which is based on micro-optical resonators is inappropriate in these kinds of situations. In order to address these issues, the paper suggests an ANN that is specifically designed for the system and makes use of the WGM sensor’s high-quality factor (Q-factor). By extending the applicability and endurance to dynamic contexts and reducing fragility problems, the ANN seeks to give high-resolution measurement. In order to minimize post-processing requirements and maintain system robustness, the study goal is for the ANN to function as a representative predictor of the WGM sensor output. The GUCnoid 1.0 humanoid robot is used in the paper as an example to show how the WGM optical sensors may improve humanoid robot performance for a variety of applications. The results of the experiments demonstrate that the sensitivity, precision, and resolution of ANN outputs and actual WGM shifts are equivalent. As a consequence, current obstacles to the widespread use of high-precision sensing in the robotics industry are removed, and the potential of ANNs as virtual substitutes or the digital twin for genuine WGM sensors in robotics systems is validated. So, this paper can be very beneficial not only to the sensing technologies that are used in robotics, which are subjected to the dynamic environments, but also to the industrial automation and human-machine interface..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250206 (2025)
Three-Dimensional Reconstruction Method Based on Infrared Deflectometry
XIONG Ping, ZHAO Jing, CHEN Jinping, HU Hao, and CAO Jiangping
Deflectometry is a non-contact and rapid detection method with high sensitivity, which can be utilized in the areas of three-dimensional (3D) reconstruction, surface quality detection, and defect location. It has important applications in the automotive industry, optical parts manufacturing, and other fields. ClassicalDeflectometry is a non-contact and rapid detection method with high sensitivity, which can be utilized in the areas of three-dimensional (3D) reconstruction, surface quality detection, and defect location. It has important applications in the automotive industry, optical parts manufacturing, and other fields. Classical deflectometry methods require the integration of slope data to reconstruct the absolute surface shape. However, the integration procedure is error-prone due to the accumulation of random errors into large shape deviations, resulting in inaccurate measurement results. In this paper, we extract the position of the centerline of the bright fringe from the stripe image and find the center of the fringe line point by point. Using the principle of triangulation, the 3D data for the object’s shaped surface can be obtained. In addition, infrared light enhances specular reflection, resulting in better deflectometry performance than that of visible light. Experiments show that the proposed method is sensitive to the changes in height and can roughly restore the surface topography of the object without calibration..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250207 (2025)
Remarks of Optical Fibers and Devices for Microfluidic Sensing: Preparation and Processing
ZHANG Xiaotong, and YUAN Tingting
With the gradual maturity of the microfluidic technology, the integration of the microfluidic chip technology and optofluidic methods in microstructured optical fibers (MOFs) has gradually formed a highly attractive new research direction. In this paper, we summarize our recent work focusing on the microfluidic sensingWith the gradual maturity of the microfluidic technology, the integration of the microfluidic chip technology and optofluidic methods in microstructured optical fibers (MOFs) has gradually formed a highly attractive new research direction. In this paper, we summarize our recent work focusing on the microfluidic sensing technology based on microhole fibers. The design and fabrication of such microfluidic fibers, device processing and fabrication techniques based on microfluidic fibers, and surface modification and coating methods for fibers are systematically introduced. Finally, several typical cases combining the optical fiber and microfluidic substance detection are presented..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250208 (2025)
Au-Nanocoated Twisted-SMF for Multiparameter Sensor
ZHAO Yifei, GU Jiexuan, SHI Weiqian, ZHANG Yuheng... and ZHOU Guiyao|Show fewer author(s)
In this paper, we experimentally demonstrated the application of the Au-nanocoated twisted single-mode fiber (Au-TSMF) structure for the response of the multiparameter. Firstly, we fabricated an Au-TSMF, which achieved high sensitivity to refractive index (RI) and torsion. Additionally, based on the theory of polarizatIn this paper, we experimentally demonstrated the application of the Au-nanocoated twisted single-mode fiber (Au-TSMF) structure for the response of the multiparameter. Firstly, we fabricated an Au-TSMF, which achieved high sensitivity to refractive index (RI) and torsion. Additionally, based on the theory of polarization interference, we amplified its polarization sensitivity and induced the phase factor caused by polarization as a wavelength shift. Ultimately, we achieved the response of the Au-TSMF structure to the multiparameter, which had the sensitivity of−0.436 dB/(deg/m) for clockwise torsion, −0.156 dB/(deg/m) for anticlockwise torsion, 0.391 5 nm/rad for the left-handed circularly polarized state, −0.926 nm/rad for the right-handed circularly polarized state, and −692.9 dB/RIU for RI. Due to the advantages of the all-fiber integrated system, this work holds great potential for facilitating fiber optic integrated devices for optical fiber biosensors and biomedical diagnostic applications..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250209 (2025)
All Optic-Fiber Waveguide-Coupled SPR Sensor for CRP Sensing Based on Dielectric Layer and Poly-Dopamine
MA Jinying, LI Shixin, HUANG Xiangdong, JIANG Junfeng... and LIU Tiegen|Show fewer author(s)
We developed an all optic-fiber waveguide-coupled surface plasmon resonance (SPR) sensor using zirconium disulfide (ZrS2) and poly-dopamine (PDA) as the dielectric layer and biological cross-linker, respectively. This sensor can be employed to monitor the entire process of the C-reactive protein (CRP) sensing, includinWe developed an all optic-fiber waveguide-coupled surface plasmon resonance (SPR) sensor using zirconium disulfide (ZrS2) and poly-dopamine (PDA) as the dielectric layer and biological cross-linker, respectively. This sensor can be employed to monitor the entire process of the C-reactive protein (CRP) sensing, including antibody modification and antigen detection. The design and the optimization of the optical fiber waveguide-coupled SPR sensor were realized, based on the transfer matrix method and first-principles calculations. The sensor was fabricated and characterized according to the optimized parameters. The experimental setup was implemented to measure the entire process of antibody modification and antigen detection for CRP with the detection limit of 3.21 pmol·mL−1, and the specificity tests were also carried out..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250224 (2025)
Different-Mode Power Splitters for Optical Testing of Three-Channel and Dual-Mode Waveguide Crossing
MA Hansi, DU Te, JIANG Xinpeng, ZHANG Zhaojian... and PENG Yuanxi|Show fewer author(s)
We study that the different-mode (waveguide-connected) power splitter [(W)PS] can provide different-mode testing points for the optical testing. With the PS or WPS providing two different-mode testing points, the measured insertion losses (ILs) of the three-channel and dual-mode waveguide crossing (WC) for both the funWe study that the different-mode (waveguide-connected) power splitter [(W)PS] can provide different-mode testing points for the optical testing. With the PS or WPS providing two different-mode testing points, the measured insertion losses (ILs) of the three-channel and dual-mode waveguide crossing (WC) for both the fundamental transverse electric (TE0) and TE1 modes are less than 1.8 dB or 1.9 dB from 1 540 nm to 1 560 nm. At the same time, the crosstalks (CTs) are lower than −17.4 dB or −18.2 dB. The consistent test results indicate the accuracy of the (W)PS-based testing circuit. Additionally, combining the tunable tap couplers, the (W)PS can provide multiple testing points with different modes and different transmittances..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250225 (2025)
Experimental Study of Fiber-Optic Temperature Sensor Based on Dual FSIs
XU Xiaotong, ZHOU Xuefang, YANG Guowei, BI Meihua... and XU Yuansheng|Show fewer author(s)
To improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaTo improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaining fibers (PMFs) with lengths of 13.62 m and 15.05 m respectively is used to achieve the basic Vernier effect. Then by changing the length of one PMF to approximately i times that of the others, the FSI composed of two PMFs of 7.1 m and 15.05 m is used to achieve the first-order harmonic Vernier effect. Afterward, temperature sensing tests are conducted to observe the wavelength drift during temperature changes and ultimately achieve high sensitivity. The experimental results show that the temperature sensitivity of the sensor based on the first-order harmonic Vernier effect is −28.89 nm/℃, which is 17.09 times that of a single FSI structure (−1.69 nm/℃) and 1.84 times that of the sensitivity generated by the structure based on the basic Vernier effect (−15.69 nm/℃). The experimental results are consistent with the theoretical analysis. The structure proposed in this paper achieves drift measurement of 0.1 ℃ variation based on 1 ℃ drift, making the fiber optic temperature sensor applicable to related fields that require high precision temperature. The proposed temperature sensor has the simple structure, low production cost, high sensitivity, and broad application prospects..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250226 (2025)
Exploration of Biologically-Inspired Nanostructures: Review on the Sensing Potential and Technological Integration of the Morpho Butterfly Wing
AHMED Mian Aizaz, HU Dingwen, SHI Yaqi, CHEN Yinpeng... and YANG Zongyin|Show fewer author(s)
The surge in demand for cost-effective, lightweight, and rapidly responsive sensors has propelled research in various fields, and traditional sensors face limitations in performing up to the mark due to their intrinsic properties and a lack of innovative fabrication techniques. Consequently, over the last decade, a notThe surge in demand for cost-effective, lightweight, and rapidly responsive sensors has propelled research in various fields, and traditional sensors face limitations in performing up to the mark due to their intrinsic properties and a lack of innovative fabrication techniques. Consequently, over the last decade, a notable shift has been toward harnessing naturally existing nanostructures to develop efficient and versatile sensing devices. One such nanostructure in morpho butterfly wings has attracted attention because of its vibrant uniqueness and diverse sensing properties. This review will explore recent interdisciplinary research endeavors on the nanostructure, including chemical, vapor, and acoustic detection. Furthermore, its potential as an infrared sensor, considerations related to heat transfer properties, and a brief overview of various replication techniques and challenges encountered in reproducing the intricate nanostructure are discussed..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250227 (2025)
Femto-Laser Processed Metasurface With Fano Response: Applications to a High Performance Refractometric Sensor
ELSHORBAGY Mahmoud H., SAN-BLAS Alejandro, SANCHEZ-BREA Luis Miguel, OLAIZOLA Santiago M.... and ALDA Javier|Show fewer author(s)
The practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs. We have engraved a split grating geometry on stainless steel using femtosecond laser processing. This structure serves as a templThe practical development of compact modern nanophotonic devices relies on the availability of fast and low-cost fabrication techniques applicable to a wide variety of materials and designs. We have engraved a split grating geometry on stainless steel using femtosecond laser processing. This structure serves as a template to fabricate efficient plasmonic sensors, where a thick gold layer is grown conformally on it. The scanning electron microscope (SEM) images confirm the generation of the split laser-induced periodic spatial structures. The optical reflectance of our sensors shows two dips corresponding to the excitation of surface plasmon resonances (SPRs) at two different wavelengths. Furthermore, the asymmetric shape of these spectral responses reveals a strong and narrow Fano resonance. Our computational electromagnetism models accurately reproduce the reflectivity of the fabricated structure. The spectral responses of both the simulated and fabricated structures are fitted to the Fano model that coherently combines the narrow SPRs with the broad continuum background caused by diffraction. The parameters extracted from the fitting, such as the resonance wavelengths and line widths, are used to evaluate the performance of our device as a refractometric sensor for liquids. The maximum sensitivity and figure of merit are 880 nm/RIU and 80 RIU−1, respectively. Besides the compact design of our sensing device, its performance exceeds the theoretical maximum sensitivity of a classical Kretschmann setup..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250228 (2025)
Ultrafast and Reproducible Fiber-Optic Hydrogen Sensor via a Tilted Fiber Grating With Pd/WO3 Nanocoating
YANG Zhiyong, YAN Xiangyu, PENG Bo, LI Zhencheng... and GUO Tuan|Show fewer author(s)
Hydrogen, a high-density and clean energy, has been widely used in various critical applications. However, the safety risk caused by hydrogen leakage during storage and transportation is still a non-negligible issue. Therefore, it is necessary to offer hydrogen sensors with fast response and high repeatability, and it Hydrogen, a high-density and clean energy, has been widely used in various critical applications. However, the safety risk caused by hydrogen leakage during storage and transportation is still a non-negligible issue. Therefore, it is necessary to offer hydrogen sensors with fast response and high repeatability, and it will be perfect for achieving in situ monitoring over the lifecycle of hydrogen production and utilization. Here, we propose a compact optical fiber sensor with a short section of the tilted Bragg fiber grating (TFBG) inscribed in the fiber core and a palladium and tungsten trioxide (Pd/WO3) combined film of 40 nm thickness over the fiber surface. The TFBG excites tens of narrow cladding resonances, part of which possess refractive indexes matching that of the Pd/WO3 coating and providing the high sensitivity to the surrounding hydrogen concentration change. The sensor offers improved sensing characteristics, including the fast response time (less than 10 s), high repeatability (over tens of measurement), and excellent linear response (higher than 99.6%) over the 0% to 3% concentration range..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250229 (2025)
Review on In-Situ Marine Monitoring Using Physical and Chemical Optical Fiber Sensors
ZHUANG Funa, LI Yu, GUO Tuan, YANG Qinghua... and WANG Shanshan|Show fewer author(s)
Optical fiber sensors (OFSs) have attracted more and more attention in the field of in-situ ocean observation because of their advantages of the small size, light weight, low cost, and intrinsic immunity to electromagnetic interference. Here, we comprehensively reviewed the development of various advanced physical and Optical fiber sensors (OFSs) have attracted more and more attention in the field of in-situ ocean observation because of their advantages of the small size, light weight, low cost, and intrinsic immunity to electromagnetic interference. Here, we comprehensively reviewed the development of various advanced physical and chemical OFSs for in-situ measurement of ocean key parameters, including temperature, salinity, pressure, acoustics, flow velocity and turbulence, potential of hydrogen (pH), heavy metal ions, nitrates, and gases. Moreover, the performances of different kinds of OFSs and their practical sea trial reports for in-situ measurement in the marine environment are provided. As we discussed, the field of OFS is rapidly evolving and is poised to make essential breakthroughs in marine monitoring, leading to better utility of marine resources..
Photonic Sensors
- Publication Date: May. 13, 2025
- Vol. 15, Issue 2, 250230 (2025)
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