Research

9 pages, 1238 KiB

Open AccessCommunication

Detection of Hemoglobin Concentration Based on Defective One-Dimensional Photonic Crystals

by Shiju Edappadikkunnummal, Rahul Chembra Vasudevan, Sruthy Dinesh, Sheenu Thomas, Narayana Rao Desai and Sharafudeen Kaniyarakkal

Photonics 2022, 9(9), 660; https://doi.org/10.3390/photonics9090660 - 16 Sep 2022

Cited by 8 | Viewed by 1531

Abstract

The significance of the optical biosensor is its ability to detect biomolecules in their natural form. Among them, photonic crystal-based biosensors analyze the refractive index changes due to molecular interaction, and that is correlated to the sample concentration instead of sample mass. In [...] Read more.

The significance of the optical biosensor is its ability to detect biomolecules in their natural form. Among them, photonic crystal-based biosensors analyze the refractive index changes due to molecular interaction, and that is correlated to the sample concentration instead of sample mass. In this paper, we report the sensing performance of a one-dimensional photonic crystal-based sensor for the detection of hemoglobin concentration using an asymmetric periodic structure with a single defect. We have used the transfer matrix method to analyze the reflectance properties of the photonic crystal. The resonant dip in the spectra and its shift with hemoglobin concentration is the basis of our sensor design. The proposed sensor is efficient in sensing hemoglobin concentration, the sensitivity and other sensor parameters were derived numerically, and the obtained parameters are comparable to the many of the reported values of photonic crystal-based sensors. The dependence of the defect layer thickness on the position of resonant dips and sensitivity is also demonstrated in our work. The numerical results prove that these photonic crystal biosensors are simple, cost effective and highly accurate for detecting the hemoglobin concentration. Full article

(This article belongs to the Special Issue Optical Sensing)

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9 pages, 2140 KiB

Open AccessArticle

A Graphene/Gold-Coated Surface Plasmon Sensor for Sodium Nitrate Detection

by H. A Zain, M. Batumalay, Z. Harith, H. R. A. Rahim and S. W. Harun

Photonics 2022, 9(8), 588; https://doi.org/10.3390/photonics9080588 - 19 Aug 2022

Viewed by 1177

Abstract

A sodium nitrate sensor with graphene/gold coating is presented in this paper. A Kretschmann setup with angle interrogation was used to detect sodium nitrate in the range of 0–15%. Using a graphene coating on top of the 50 nm gold layer showed an [...] Read more.

A sodium nitrate sensor with graphene/gold coating is presented in this paper. A Kretschmann setup with angle interrogation was used to detect sodium nitrate in the range of 0–15%. Using a graphene coating on top of the 50 nm gold layer showed an improvement in the sensitivity of the sensor. The gold-coated setups had a sensitivity of 0.198°/%. In contrast, the graphene/gold-coated samples showed a sensitivity of 0.244°/% due to the charge transfer between the graphene and the gold and the resulting excited solid electric field. The graphene/gold-coated sensor showed good stability with time in the temperature range of 19–34 °C. This shows that this setup may be beneficial in detecting sodium nitrate. Full article

(This article belongs to the Special Issue Optical Sensing)

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10 pages, 2426 KiB

Open AccessArticle

Maritime Infrared and Visible Image Fusion Based on Refined Features Fusion and Sobel Loss

by Zongjiang Gao, Feixiang Zhu, Haili Chen and Baoshan Ma

Photonics 2022, 9(8), 566; https://doi.org/10.3390/photonics9080566 - 11 Aug 2022

Cited by 1 | Viewed by 1355

Abstract

Infrared (IR) and visible image fusion has become an important technology for maritime environment awareness. In this study, we employed refined features fusion and Sobel loss for maritime IR and visible image fusion. First, we used the encoder in Densefuse net to transform [...] Read more.

Infrared (IR) and visible image fusion has become an important technology for maritime environment awareness. In this study, we employed refined features fusion and Sobel loss for maritime IR and visible image fusion. First, we used the encoder in Densefuse net to transform the image to be fused from the pixel domain to the feature domain. Then, the features’ information was accurately measured, and the refined features were fused and sent to the decoder to reconstruct the fused images. Mixed loss, commonly employed in image fusion, eliminates the effect of different losses but also introduces hyperparameters. We innovatively used Sobel loss to measure the input and fused images to reduce the hyperparameters in the loss function. Finally, experiments were performed, and our algorithm achieved good fusion results in the qualitative and quantitative evaluations. Full article

(This article belongs to the Special Issue Optical Sensing)

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13 pages, 4398 KiB

Open AccessArticle

Research on Tunable SPR Sensors Based on WS₂ and Graphene Hybrid Nanosheets

by Di Wang, Jin Liu, Haima Yang, Bo Huang and Guohui Zeng

Photonics 2022, 9(7), 490; https://doi.org/10.3390/photonics9070490 - 12 Jul 2022

Cited by 5 | Viewed by 1739

Abstract

A prismatic excitation-based affinity biosensor consisting of the prism (BK7), WS₂/graphene hybrid nanosheets, and silver (Ag) as the active metal for the surface plasmon resonance is proposed in this present research. The introduction of the transition metal WS₂/graphene layer [...] Read more.

A prismatic excitation-based affinity biosensor consisting of the prism (BK7), WS₂/graphene hybrid nanosheets, and silver (Ag) as the active metal for the surface plasmon resonance is proposed in this present research. The introduction of the transition metal WS₂/graphene layer protected the silver substrate and enhanced the adsorption of biomolecules, which facilitated the quality and performance of detection. Here, we improved the detection structure by focusing on the metallic materials, graphene and WS₂ film layers, and the thickness of the measured medium on the sensing effect. The results show that the silver film had a more desirable resonance effect, and the design of the symmetric detection structure produced a double resonance peak, and it provides a reference for distributed sensing. Changing the thickness of the detection medium can dynamically adjust the wave vector matching conditions, which gives the sensor a certain tunability. In the bilayer WS₂ and monolayer graphene (W = 2, G = 1) configuration, the sensitivity was up to 224 deg/RIU with a quality factor of 96.97 RIU⁻¹, which has potential for clinical analytic and biochemical detecting applications. Full article

(This article belongs to the Special Issue Optical Sensing)

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15 pages, 26874 KiB

Open AccessArticle

Sputtering Deposition of TiO₂ Thin Film Coatings for Fiber Optic Sensors

by Daniela Silva, Catarina S. Monteiro, Susana O. Silva, Orlando Frazão, Joana V. Pinto, Maria Raposo, Paulo A. Ribeiro and Susana Sério

Photonics 2022, 9(5), 342; https://doi.org/10.3390/photonics9050342 - 13 May 2022

Cited by 2 | Viewed by 2227

Abstract

Thin films of titanium dioxide (TiO₂) and titanium (Ti) were deposited onto glass and optical fiber supports through DC magnetron sputtering, and their transmission was characterized with regard to their use in optical fiber-based sensors. Deposition parameters such as oxygen partial [...] Read more.

Thin films of titanium dioxide (TiO₂) and titanium (Ti) were deposited onto glass and optical fiber supports through DC magnetron sputtering, and their transmission was characterized with regard to their use in optical fiber-based sensors. Deposition parameters such as oxygen partial pressure, working pressure, and sputtering power were optimized to attain films with a high reflectance. The films deposited on glass supports were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Regarding the deposition parameters, all three parameters were tested simultaneously, changing the working pressure, the sputtering power, and the oxygen percentage. It was possible to conclude that a lower working pressure and higher applied power lead to films with a higher reflectance. Through the analysis of the as-sputtered thin films using X-ray diffraction, the deposition of both Ti and TiO₂ films was confirmed. To study the applicability of TiO₂ and Ti in fiber sensing, several thin films were deposited in single mode fibers (SMFs) using the sputtering conditions that revealed the most promising results in the glass supports. The sputtered TiO₂ and Ti thin films were used as mirrors to increase the visibility of a low-finesse Fabry–Perot cavity and the possible sensing applications were studied. Full article

(This article belongs to the Special Issue Optical Sensing)

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14 pages, 5687 KiB

Open AccessArticle

Accurate Depth Recovery Method Based on the Fusion of Time-of-Flight and Dot-Coded Structured Light

by Feifei Gu, Huazhao Cao, Pengju Xie and Zhan Song

Photonics 2022, 9(5), 333; https://doi.org/10.3390/photonics9050333 - 11 May 2022

Cited by 1 | Viewed by 2139

Abstract

3D vision technology has been gradually applied to intelligent terminals ever since Apple Inc. introduced structured light on iPhoneX. At present, time-of-flight (TOF) and laser speckle-based structured light (SL) are two mainstream technologies applied to intelligent terminals, both of which are widely regarded [...] Read more.

3D vision technology has been gradually applied to intelligent terminals ever since Apple Inc. introduced structured light on iPhoneX. At present, time-of-flight (TOF) and laser speckle-based structured light (SL) are two mainstream technologies applied to intelligent terminals, both of which are widely regarded as efficient dynamic technologies, but with low accuracy. This paper explores a new approach to achieve accurate depth recovery by fusing TOF and our previous work—dot-coded SL (DCSL). TOF can obtain high-density depth information, but its results may be deformed due to multi-path interference (MPI) and reflectivity-related deviations. In contrast, DCSL can provide high-accuracy and noise-clean results, yet only a limited number of encoded points can be reconstructed. This inspired our idea to fuse them to obtain better results. In this method, the sparse result provided by DCSL can work as accurate “anchor points” to keep the correctness of the target scene’s structure, meanwhile, the dense result from TOF can guarantee full-range measurement. Experimental results show that by fusion, the MPI errors of TOF can be eliminated effectively. Dense and accurate results can be obtained successfully, which has great potential for application in the 3D vision task of intelligent terminals in the future. Full article

(This article belongs to the Special Issue Optical Sensing)

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15 pages, 4758 KiB

Open AccessArticle

Ultra-Sensitive Si-Based Optical Sensor for Nanoparticle-Size Traditional Water Pollutant Detection

by Ahmed Emara, Amr Yousef and Khaled Elleithy

Photonics 2022, 9(5), 289; https://doi.org/10.3390/photonics9050289 - 23 Apr 2022

Viewed by 1722

Abstract

A low-cost Si-based optical nano-sensor that monitors traditional water pollutants is introduced in this paper. The introduced sensor works in the near-infrared region, 900 nm to 2500 nm spectral range. The proposed structure consists of a Si layer with an optimized thickness of [...] Read more.

A low-cost Si-based optical nano-sensor that monitors traditional water pollutants is introduced in this paper. The introduced sensor works in the near-infrared region, 900 nm to 2500 nm spectral range. The proposed structure consists of a Si layer with an optimized thickness of 300 nm on the top of the Al layer acting as a back reflector. On the top of the Si layer, the water pollutants are modeled as nanoparticle materials of different sizes. The finite difference time domain method is utilized to optimize the thicknesses of the Si layer by analyzing the optical light absorption considering different Si layer thicknesses and different pollutant nanoparticles’ sizes. Different interpolation techniques, including polynomials with various degrees and locally weighted smoothing quadratic regression, are used to find the best fitting model representing the simulated data points with goodness of fit analysis. Three features are proposed to identify the water pollutant with its size, peak absorption wavelength, relative amplitude, and a full width at half maximum. The device’s performance in detecting six different pollutants, silver, aluminum, copper, chromium, selenium, and ammonia, is evaluated. Sensitivity, a figure of merit, and a quality factor are used to evaluate the proposed sensor. The obtained maximum sensitivity is 11,300 nm/RIU, FOM of 740, and quality factor of 670. Full article

(This article belongs to the Special Issue Optical Sensing)

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11 pages, 971 KiB

Open AccessArticle

Sagnac Loop Based Sensing System for Intrusion Localization Using Machine Learning

by Maged A. Esmail, Jameel Ali, Esam Almohimmah, Ahmed Almaiman, Amr M. Ragheb and Saleh Alshebeili

Photonics 2022, 9(5), 275; https://doi.org/10.3390/photonics9050275 - 20 Apr 2022

Cited by 7 | Viewed by 1922

Abstract

Among all optical sensing techniques, the distributed Sagnac loop (SI) sensor has the advantage of being simple to implement with low cost. Most of the proposed techniques for using SI exploit the frequency null method for event localization. However, such a technique suffers [...] Read more.

Among all optical sensing techniques, the distributed Sagnac loop (SI) sensor has the advantage of being simple to implement with low cost. Most of the proposed techniques for using SI exploit the frequency null method for event localization. However, such a technique suffers from the low spectrum signal power, complicating event localization under environmental noise. In this work, event localization using time-domain instead of frequency null signals is achieved using machine learning (ML), which is increasingly being exploited in many science fields, including sensing applications. First, a training dataset that includes 200 events is generated over a 50 km effective sensing fiber. These time-domain signals are considered as features for training the ML algorithm. Then, the random forest (RF) ML algorithm is used to develop a model for event location prediction. The results show the capability of ML in predicting the event’s location with 55 m mean absolute error (MAE). Further, the percentage of test realizations with prediction error > 200 m is 0.7%. The sensing signal bandwidth is investigated, showing better performance results for sensing signals of larger bandwidths. Finally, the proposed model is validated experimentally. The results showed good accuracy with MAE < 100 m. Full article

(This article belongs to the Special Issue Optical Sensing)

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9 pages, 3759 KiB

Open AccessCommunication

Scanning Angle Magnification with Compact Reflective Optics for Light Detection and Ranging

by Cheng-Ta Mu, Po-Cheng Chang and Cheng-Huan Chen

Photonics 2022, 9(2), 59; https://doi.org/10.3390/photonics9020059 - 24 Jan 2022

Cited by 2 | Viewed by 2313

Abstract

The function of lidar requests a large scanning angle for a wide field of view and a well calibrated collimation of the laser beam for distant sensing. Besides meeting the required functionality, the compact form factor of the whole optical system is also [...] Read more.

The function of lidar requests a large scanning angle for a wide field of view and a well calibrated collimation of the laser beam for distant sensing. Besides meeting the required functionality, the compact form factor of the whole optical system is also highly desirable for the ease of being installed in mobile systems. In corresponding to the currently developed phase array laser which can achieve beam scanning without mechanical movement but still with a small scanning angle, a compact optics consisting of only two reflective surfaces has been proposed to magnify the scanning angle of a laser beam up to seven times while keeping the divergence of the laser beam smaller than 8 mrad for some short distance applications. The prototype has been prepared and evaluated with the expected performance. Full article

(This article belongs to the Special Issue Optical Sensing)

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11 pages, 2779 KiB

Open AccessArticle

High Sensitivity Fiber Gas Pressure Sensor with Two Separated Fabry–Pérot Interferometers Based on the Vernier Effect

by Xiaokang Song, Liangtao Hou, Xiangyu Wei, Hang Su, Chang Li, Yan Li and Lingling Ran

Photonics 2022, 9(1), 31; https://doi.org/10.3390/photonics9010031 - 04 Jan 2022

Cited by 11 | Viewed by 2146

Abstract

A high sensitivity optical fiber gas pressure sensor based on paralleled Fabry–Pérot interferometers (FPIs) was demonstrated. One micro-cavity FPI is used as a reference FPI (FPI-1) to generate a Vernier effect and the other FPI (FPI-2) is used as a sensing tip. Both [...] Read more.

A high sensitivity optical fiber gas pressure sensor based on paralleled Fabry–Pérot interferometers (FPIs) was demonstrated. One micro-cavity FPI is used as a reference FPI (FPI-1) to generate a Vernier effect and the other FPI (FPI-2) is used as a sensing tip. Both FPIs are connected by a 3-dB coupler to form a paralleled structure. The FPI-1 was fabricated by fusion splicing a piece of hollow core fiber (HCF) between two sections of single-mode fibers (SMF), whereas FPI-2 was formed by fusion splicing a section of HCF between SMF and a piece of HCF with a slightly smaller inner diameter for sensing pressure. The gas pressure sensitivity was amplified from 4 nm/MPa of single FPI to 45.76 nm/MPa of paralleled FPIs with an amplification factor of 11.44 and a linearity of 99.9%. Compared with the traditional fiber gas pressure sensors, the proposed sensor showed great advantages in sensitivity, mechanical strength, cost, and temperature influence resistant, which has potential in adverse-circumstance gas pressure sensing. Full article

(This article belongs to the Special Issue Optical Sensing)

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Graphical abstract

15 pages, 6745 KiB

Open AccessArticle

A Method of Range Walk Error Correction in SiPM LiDAR with Photon Threshold Detection

by Runze Yang, Yumei Tang, Zeyu Fu, Jian Qiu and Kefu Liu

Photonics 2022, 9(1), 24; https://doi.org/10.3390/photonics9010024 - 01 Jan 2022

Cited by 3 | Viewed by 3173

Abstract

A silicon photomultiplier (SiPM) LiDAR with photon threshold detection can achieve high dynamic performance. However, the number fluctuations of echo signal photons lead to the range walk error (RWE) in SiPM LIDARs. This paper derives the RWE model of SiPM LiDAR by using [...] Read more.

A silicon photomultiplier (SiPM) LiDAR with photon threshold detection can achieve high dynamic performance. However, the number fluctuations of echo signal photons lead to the range walk error (RWE) in SiPM LIDARs. This paper derives the RWE model of SiPM LiDAR by using the LiDAR equation and statistical property of SiPM’s response. Based on the LiDAR system parameters and the echo signal intensity, which is obtained through the SiPM’s photon-number-resolving capability, the RWE is calculated through the proposed model. After that, we carry out experiments to verify its effectiveness. The result shows that the method reduces the RWE in TOF measurements using photon threshold detection from 36.57 cm to the mean deviation of 1.95 cm, with the number of detected photons fluctuating from 1.3 to 46.5. Full article

(This article belongs to the Special Issue Optical Sensing)

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12 pages, 3614 KiB

Open AccessArticle

Fast Measurement of Brillouin Frequency Shift in Optical Fiber Based on a Novel Feedforward Neural Network

by Fen Xiao, Mingxing Lv and Xinwan Li

Photonics 2021, 8(11), 474; https://doi.org/10.3390/photonics8110474 - 25 Oct 2021

Cited by 3 | Viewed by 1619

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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14 pages, 4325 KiB

Open AccessArticle

Accurate 3D Shape Reconstruction from Single Structured-Light Image via Fringe-to-Fringe Network

by Hieu Nguyen and Zhaoyang Wang

Photonics 2021, 8(11), 459; https://doi.org/10.3390/photonics8110459 - 20 Oct 2021

Cited by 18 | Viewed by 3119

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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24 pages, 12492 KiB

Open AccessArticle

A Preliminary Assessment of an FBG-Based Hard Landing Monitoring System

by Angela Brindisi, Cristian Vendittozzi, Lidia Travascio, Luigi Di Palma, Michele Ignarra, Vincenzo Fiorillo and Antonio Concilio

Photonics 2021, 8(10), 450; https://doi.org/10.3390/photonics8100450 - 17 Oct 2021

Cited by 8 | Viewed by 2367

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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10 pages, 1623 KiB

Open AccessCommunication

Highly Sensitive Biosensor Based on Partially Immobilized Silver Nanopillars in the Terahertz Band

by Shuo Liu, Lin Li and Zhenxu Bai

Photonics 2021, 8(10), 438; https://doi.org/10.3390/photonics8100438 - 13 Oct 2021

Cited by 4 | Viewed by 1476

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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15 pages, 2430 KiB

Open AccessArticle

Dual-Modality Imaging Microfluidic Cytometer for Onsite Detection of Phytoplankton

by Bo Xiong, Tianqi Hong, Herbert Schellhorn and Qiyin Fang

Photonics 2021, 8(10), 435; https://doi.org/10.3390/photonics8100435 - 12 Oct 2021

Cited by 1 | Viewed by 2063

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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11 pages, 4222 KiB

Open AccessCommunication

Optical Detection of VOC Vapors Using Nb₂O₅ Bragg Stack in Transmission Mode

by Rosen Georgiev, Yoana Chorbadzhiyska, Venelin Pavlov, Biliana Georgieva and Tsvetanka Babeva

Photonics 2021, 8(9), 399; https://doi.org/10.3390/photonics8090399 - 18 Sep 2021

Cited by 1 | Viewed by 1547

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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11 pages, 5361 KiB

Open AccessCommunication

Ultra-Sensitive Intensity Modulated Strain Sensor by Tapered Thin-Core Fiber Based Modal Interferometer

by Chuanxu Liu, Dexue Sun, Jiuru Yang, Hui Zhang and Lingling Ran

Photonics 2021, 8(9), 372; https://doi.org/10.3390/photonics8090372 - 03 Sep 2021

Cited by 5 | Viewed by 2107

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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12 pages, 3755 KiB

Open AccessArticle

Magnetic Field Sensing Characteristics Based on Optical Microfiber Coupler Interferometer and Magnetic Fluid

by Shangpeng Qin, Junyang Lu, Minwei Li, Yang Yu, Junbo Yang and Zhenrong Zhang

Photonics 2021, 8(9), 364; https://doi.org/10.3390/photonics8090364 - 30 Aug 2021

Cited by 4 | Viewed by 1799

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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14 pages, 5773 KiB

Open AccessArticle

Theoretical Considerations of Photonic Crystal Fiber with All Uniform-Sized Air Holes for Liquid Sensing

by Abdul Mu’iz Maidi, Pg Emeroylarffion Abas, Pg Iskandar Petra, Shubi Kaijage, Nianyu Zou and Feroza Begum

Photonics 2021, 8(7), 249; https://doi.org/10.3390/photonics8070249 - 30 Jun 2021

Cited by 19 | Viewed by 1890

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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14 pages, 2345 KiB

Open AccessArticle

Development of a Temperature-Controlled Optical Planar Waveguide Sensor with Lossy Mode Resonance for Refractive Index Measurement

by Yu-Cheng Lin and Liang-Yü Chen

Photonics 2021, 8(6), 199; https://doi.org/10.3390/photonics8060199 - 04 Jun 2021

Cited by 1 | Viewed by 2846

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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12 pages, 2195 KiB

Open AccessArticle

Computational Method for Wavefront Sensing Based on Transport-of-Intensity Equation

by Iliya Gritsenko, Michael Kovalev, George Krasin, Matvey Konoplyov and Nikita Stsepuro

Photonics 2021, 8(6), 177; https://doi.org/10.3390/photonics8060177 - 22 May 2021

Cited by 6 | Viewed by 2994

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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14 pages, 4713 KiB

Open AccessArticle

Generalized Resonance Sensor Based on Fiber Bragg Grating

by Xinxin Chen, Enbo Wang, Yali Jiang, Hui Zhan, Hongwei Li, Guohui Lyu and Shuli Sun

Photonics 2021, 8(5), 156; https://doi.org/10.3390/photonics8050156 - 06 May 2021

Cited by 3 | Viewed by 2023

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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11 pages, 2502 KiB

Open AccessArticle

Study on the Nanosensor Based on a MIM Waveguide with a Stub Coupled with a Horizontal B-Type Cavity

by Shubin Yan, Haoran Shi, Xiaoyu Yang, Jing Guo, Wenchang Wu and Ertian Hua

Photonics 2021, 8(4), 125; https://doi.org/10.3390/photonics8040125 - 16 Apr 2021

Cited by 3 | Viewed by 1853

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 H_Z 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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14 pages, 7238 KiB

Open AccessArticle

Design and Simulation of Photonic Crystal Fiber for Liquid Sensing

by Abdul Mu’iz Maidi, Izaddeen Yakasai, Pg Emeroylariffion Abas, Malik Muhammad Nauman, Rosyzie Anna Apong, Shubi Kaijage and Feroza Begum

Photonics 2021, 8(1), 16; https://doi.org/10.3390/photonics8010016 - 12 Jan 2021

Cited by 37 | Viewed by 3972

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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