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Selected Papers from the 5th International Conference on Applications of Optics and Photonics (AOP2022)

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

Deadline for manuscript submissions: closed (25 June 2023) | Viewed by 17178

Special Issue Editors


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Guest Editor
Center of Physics of the Universities of Minho and Porto, School of Sciences, University of Minho, 4710-057 Braga, Portugal
Interests: optical metrology; image processing; thin films, micro- and nanostructures and systems; optics and science education
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Guest Editor
INESC-Tec, University of Porto, Porto, Portugal
Interests: optical sensors

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Guest Editor
Instituto de Telecomunicações, University of Aveiro, Aveiro, Portugal
Interests: optical communications and sensors

Special Issue Information

Dear Colleagues,

The 5th International Conference on Applications of Optics and Photonics (AOP2021) will be held in Guimarães (Portugal), 19–23 July 2021. Since its first edition back in 2011, the AOP conference has provided an excellent opportunity to foster, in an open and friendly environment, the establishment of the widest range of cooperation projects and relationships with colleagues and institutions involved in optics and photonics research from all around the world. With this conference, open to contributions in all domains of optics and photonics and application fields, we expect to review the state of the art in these subjects and to foresee and discuss the future of research in optics and photonics. A large number of plenary and keynote lectures by world-renowned researchers in all fields of optics and photonics will set the quality standards of a varied and exciting scientific program.

We are honored to serve as Guest Editors of this Special Issue to be published in Sensors that will contain a selection of papers submitted and accepted at the AOP2021 conference in subjects relevant to the Sensors journal. Its main scope is to provide a timely and broad collection of the most innovative topics discussed at the latest edition of the conference related to applications of optics and photonics. We warmly invite researchers to submit their contributions, both original research articles and review papers, to this Special Issue. Topics include but are not limited to the following:

  • Nanophotonics, plasmonics, theoretical optics, and quantum and nonlinear optics;
  • Optical communications and sensors;
  • Optical fibers and applications;
  • Biophotonics and biomedical and medical applications of optics and photonics;
  • Ultrafast lasers, ultrafast optics, and power lasers;
  • Optical metrology, image processing, and industrial applications;
  • Optometry, ophthalmic optics, and color and visual sciences;
  • Optoelectronics;
  • Microwave photonics;
  • Photonics and optical instrumentation for space and astronomy;
  • Optics and photonics for smart mobility and smart cities.

Prof. Dr. Manuel Filipe P. C. M. Costa
Prof. Dr. Orlando Frazão
Prof. Dr. Rogerio Nogueira
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

  • Nanophotonics, plasmonics, theoretical optics, and quantum and nonlinear optics 
  • Optical communications and sensors 
  • Optical fibers and applications 
  • Biophotonics and biomedical and medical applications of optics and photonics 
  • Ultrafast lasers, ultrafast optics, and power lasers 
  • Optical metrology, image processing, and industrial applications 
  • Optometry, ophthalmic optics, and color and visual sciences 
  • Optoelectronics 
  • Microwave photonics 
  • Photonics and optical instrumentation for space and astronomy 
  • Optics and photonics for smart mobility and smart cities

Published Papers (10 papers)

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Research

11 pages, 3898 KiB  
Communication
A Fiber Optic Sensor for Monitoring the Spectral Alterations and Depth in Ex Vivo and In Vivo Cryosurgery
by Aris Ikiades, Ioannis D. Bassukas and Nikolaos Kourkoumelis
Sensors 2023, 23(5), 2690; https://doi.org/10.3390/s23052690 - 01 Mar 2023
Viewed by 1018
Abstract
This article discusses how to monitor the freezing depth during cryotherapy using a fiber optic array sensor. The sensor was used to measure the backscattered and transmitted light from frozen and unfrozen ex vivo porcine tissue and in vivo human skin tissue (finger). [...] Read more.
This article discusses how to monitor the freezing depth during cryotherapy using a fiber optic array sensor. The sensor was used to measure the backscattered and transmitted light from frozen and unfrozen ex vivo porcine tissue and in vivo human skin tissue (finger). The technique exploited the variations in optical diffusion properties of the frozen and unfrozen tissues to determine the extent of freezing. Ex vivo and in vivo measurements yielded comparable results, despite spectral variations attributable to the hemoglobin absorption peak in the human frozen and unfrozen tissues. However, because the spectral fingerprints of the freeze-thaw process in the ex vivo and in vivo experiments were similar, we could extrapolate the maximum depth of freezing. Therefore, this sensor has the potential to be utilized for monitoring cryosurgery in real time. Full article
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14 pages, 6209 KiB  
Article
Nonlinear Encryption for Multiple Images Based on a Joint Transform Correlator and the Gyrator Transform
by Ronal A. Perez, Juan M. Vilardy, Elisabet Pérez-Cabré, María S. Millán and Cesar O. Torres
Sensors 2023, 23(3), 1679; https://doi.org/10.3390/s23031679 - 03 Feb 2023
Cited by 4 | Viewed by 1341
Abstract
A novel nonlinear encryption–decryption system based on a joint transform correlator (JTC) and the Gyrator transform (GT) for the simultaneous encryption and decryption of multiple images in grayscale is proposed. This security system features a high level of security for the single real-valued [...] Read more.
A novel nonlinear encryption–decryption system based on a joint transform correlator (JTC) and the Gyrator transform (GT) for the simultaneous encryption and decryption of multiple images in grayscale is proposed. This security system features a high level of security for the single real-valued encrypted image and a high image quality for the multiple decrypted images. The multispectral or color images are considered as a special case, taking each color component as a grayscale image. All multiple grayscale images (original images) to encrypt are encoded in phase and placed in the input plane of the JTC at the same time without overlapping. We introduce two random-phase masks (RPMs) keys for each image to encrypt at the input plane of the JTC-based encryption system. The total number of the RPM keys is given by the double of the total number of the grayscale images to be encrypted. The use of several RPMs as keys improves the security of the encrypted image. The joint Gyrator power distribution (JGPD) is the intensity of the GT of the input plane of the JTC. We obtain only a single real-valued encrypted image with a high level of security for all the multiple grayscale images to encrypt by introducing two new suitable nonlinear modifications on the JGPD. The security keys are given by the RPMs and the rotation angle of the GT. The decryption system is implemented by two successive GTs applied to the encrypted image and the security keys given by the RPMs and considering the rotation angle of the GT. We can simultaneously retrieve the various information of the original images at the output plane of the decryption system when all the security keys are correct. Another result due to the appropriate definition of the two nonlinear operations applied on the JGPD is the retrieval of the multiple decrypted images with a high image quality. The numerical simulations are computed with the purpose of demonstrating the validity and performance of the novel encryption–decryption system. Full article
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16 pages, 14906 KiB  
Article
Spectral Analysis Methods for Improved Resolution and Sensitivity: Enhancing SPR and LSPR Optical Fiber Sensing
by Paulo S. S. Dos Santos, João P. Mendes, Bernardo Dias, Jorge Pérez-Juste, José M. M. M. De Almeida, Isabel Pastoriza-Santos and Luis C. C. Coelho
Sensors 2023, 23(3), 1666; https://doi.org/10.3390/s23031666 - 02 Feb 2023
Cited by 6 | Viewed by 2050
Abstract
Biochemical–chemical sensing with plasmonic sensors is widely performed by tracking the responses of surface plasmonic resonance peaks to changes in the medium. Interestingly, consistent sensitivity and resolution improvements have been demonstrated for gold nanoparticles by analyzing other spectral features, such as spectral inflection [...] Read more.
Biochemical–chemical sensing with plasmonic sensors is widely performed by tracking the responses of surface plasmonic resonance peaks to changes in the medium. Interestingly, consistent sensitivity and resolution improvements have been demonstrated for gold nanoparticles by analyzing other spectral features, such as spectral inflection points or peak curvatures. Nevertheless, such studies were only conducted on planar platforms and were restricted to gold nanoparticles. In this work, such methodologies are explored and expanded to plasmonic optical fibers. Thus, we study—experimentally and theoretically—the optical responses of optical fiber-doped gold or silver nanospheres and optical fibers coated with continuous gold or silver thin films. Both experimental and numerical results are analyzed with differentiation methods, using total variation regularization to effectively minimize noise amplification propagation. Consistent resolution improvements of up to 2.2× for both types of plasmonic fibers are found, demonstrating that deploying such analysis with any plasmonic optical fiber sensors can lead to sensing resolution improvements. Full article
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11 pages, 954 KiB  
Article
Convolution, Correlation and Generalized Shift Operations Based on the Fresnel Transform
by Juan M. Vilardy, Eder Alfaro and Johonfri Mendoza
Sensors 2023, 23(3), 1663; https://doi.org/10.3390/s23031663 - 02 Feb 2023
Viewed by 1199
Abstract
The Fresnel transform (FrT) is commonly used to describe the free-space propagation of optical waves. In this work, we present new definitions for the convolution, correlation and generalized shift operations based on the FrT. The generalized shift operation is defined by using simultaneous [...] Read more.
The Fresnel transform (FrT) is commonly used to describe the free-space propagation of optical waves. In this work, we present new definitions for the convolution, correlation and generalized shift operations based on the FrT. The generalized shift operation is defined by using simultaneous space and phase shifts. The generalized shift operation is useful for centred optical systems in the Fresnel domain (FrD) when the data distributions at the input plane of the optical system are shifted. The new convolution and correlation operations defined in terms of the FrT, the wavelength and the propagation distance, can be considered as a generalization of the usual convolution and correlation operations. The sampling theorem for distributions, whose resulting FrT has finite support, is formulated by using the new convolution operation introduced in this work and a new definition of the Dirac comb function. These new definitions and results could be applied to describe, design and implement optical processing systems related to the FrT. Finally, we present a centred optical systems used in holography and optical security systems that can be described or modelled by the new definitions of the operations proposed in this paper. Full article
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12 pages, 2016 KiB  
Article
Double Image Encryption System Using a Nonlinear Joint Transform Correlator in the Fourier Domain
by Ronal A. Perez, Elisabet Pérez-Cabré, Juan M. Vilardy, María S. Millán and Cesar O. Torres
Sensors 2023, 23(3), 1641; https://doi.org/10.3390/s23031641 - 02 Feb 2023
Viewed by 1452
Abstract
In this work, we present a new nonlinear joint transform correlator (JTC) architecture in the Fourier domain (FD) for the encryption and decryption of two simultaneous images. The main features of the proposed system are its increased level of security, the obtention of [...] Read more.
In this work, we present a new nonlinear joint transform correlator (JTC) architecture in the Fourier domain (FD) for the encryption and decryption of two simultaneous images. The main features of the proposed system are its increased level of security, the obtention of a single real-valued encrypted signal that contains the ciphered information of the two primary images and, additionally, a high image quality for the two final decrypted signals. The two images to be encrypted can be either related to each other, or independent signals. The encryption system is based on the double random phase encoding (DRPE), which is implemented by using a nonlinear JTC in the FD. The input plane of the JTC has four non-overlapping data distributions placed side-by-side with no blank spaces between them. The four data distributions are phase-only functions defined by the two images to encrypt and four random phase masks (RPMs). The joint power spectrum (JPS) is produced by the intensity of the Fourier transform (FT) of the input plane of the JTC. One of the main novelties of the proposal consists of the determination of the appropriate two nonlinear operations that modify the JPS distribution with a twofold purpose: to obtain a single real-valued encrypted image with a high level of security and to improve the quality of the decrypted images. The security keys of the encryption system are represented by the four RPMs, which are all necessary for a satisfactory decryption. The decryption system is implemented using a 4f-processor where the encrypted image and the security keys given by the four RPMs are introduced in the proper plane of the processor. The double image encryption system based on a nonlinear JTC in the FD increases the security of the system because there is a larger key space, and we can simultaneously validate two independent information signals (original images to encrypt) in comparison to previous similar proposals. The feasibility and performance of the proposed double image encryption and decryption system based on a nonlinear JTC are validated through computational simulations. Finally, we additionally comment on the proposed security system resistance against different attacks based on brute force, plaintext and deep learning. Full article
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13 pages, 2654 KiB  
Article
Computational Investigation of Advanced Refractive Index Sensor Using 3-Dimensional Metamaterial Based Nanoantenna Array
by Sneha Verma and B.M.A. Rahman
Sensors 2023, 23(3), 1290; https://doi.org/10.3390/s23031290 - 23 Jan 2023
Cited by 4 | Viewed by 1584
Abstract
Photonic researchers are increasingly exploiting nanotechnology due to the development of numerous prevalent nanosized manufacturing technologies, which has enabled novel shape-optimized nanostructures to be manufactured and investigated. Hybrid nanostructures that integrate dielectric resonators with plasmonic nanostructures are also offering new opportunities. In this [...] Read more.
Photonic researchers are increasingly exploiting nanotechnology due to the development of numerous prevalent nanosized manufacturing technologies, which has enabled novel shape-optimized nanostructures to be manufactured and investigated. Hybrid nanostructures that integrate dielectric resonators with plasmonic nanostructures are also offering new opportunities. In this work, we have explored a hybrid coupled nano-structured antenna with stacked multilayer lithium tantalate (LiTaO3) and Aluminum oxide (Al2O3), operating at wavelength ranging from 400 nm to 2000 nm. Here, the sensitivity response has been explored of these nano-structured hybrid arrays. It shows a strong electromagnetic confinement in the separation gap (g) of the dimers due to strong surface plasmon resonance (SPR). The influences of the structural dimensions have been investigated to optimize the sensitivity. The designed hybrid coupled nanostructure with the combination of 10 layers of gold (Au) and Lithium tantalate (LiTaO3) or Aluminum oxide (Al2O3) (five layers each) having height, h1 = h2 = 10 nm exhibits 730 and 660 nm/RIU sensitivity, respectively. The sensitivity of the proposed hybrid nanostructure has been compared with a single metallic (only gold) elliptical paired nanostructure. Depending on these findings, we demonstrated that a roughly two-fold increase in the sensitivity (S) can be obtained by utilizing a hybrid coupled nanostructure compared to an identical nanostructure, which competes with traditional sensors of the same height, (h). Our innovative novel plasmonic hybrid nanostructures provide a framework for developing plasmonic nanostructures for use in various sensing applications. Full article
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14 pages, 4381 KiB  
Article
Detection of 2-Furaldehyde in Milk by MIP-Based POF Chips Combined with an SPR-POF Sensor
by Giancarla Alberti, Francesco Arcadio, Maria Pesavento, Chiara Marzano, Luigi Zeni, Naji Abi Zeid and Nunzio Cennamo
Sensors 2022, 22(21), 8289; https://doi.org/10.3390/s22218289 - 28 Oct 2022
Cited by 3 | Viewed by 1520
Abstract
An innovative optical-chemical sensor has been used to detect the 2-furaldehyde (2-FAL) in milk. The proposed sensing approach exploits the refractive index changing in a microstructured chip based on a plastic optical fiber (POF) with orthogonal micro-holes containing a specific molecularly imprinted polymer [...] Read more.
An innovative optical-chemical sensor has been used to detect the 2-furaldehyde (2-FAL) in milk. The proposed sensing approach exploits the refractive index changing in a microstructured chip based on a plastic optical fiber (POF) with orthogonal micro-holes containing a specific molecularly imprinted polymer (MIP). This POF-MIP chemical chip modifies the surface plasmon resonance (SPR) phenomena excited in another sensor chip realized in POFs (SPR-POF) and connected in series. The proposed sensor configuration exploits MIP receptors avoiding any modification of the gold film of the SPR platform. This work reports the performance, particularly the high sensitivity and low detection limit, in complex matrices such as buffalo milk fortified with 2-FAL and in different commercial kinds of cow milk thermally treated for pasteurization. The measurements were carried out in about ten minutes by dropping the solution under-test on the planar D-shaped POF surface of the chemical chip. In contrast, on the gold surface of the SPR-POF platform, a water drop is always placed to excite the SPR phenomenon, which is modulated by the chemical chip via MIP-2-FAL binding. Furthermore, the experimental results demonstrated the pros and cons of the proposed sensor system. Thanks to the high sensitivity of the sensor system, the detection of 2-FAL in the diluted milk sample (1:50) was achieved. The dilution is required to reduce the interferent effect of the complex matrix. Full article
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13 pages, 39719 KiB  
Article
Optical Strain Gauge Prototype Based on a High Sensitivity Balloon-like Interferometer and Additive Manufacturing
by Victor H. R. Cardoso, Paulo Caldas, Maria Thereza R. Giraldi, Orlando Frazão, João C. W. Albuquerque Costa and José Luís Santos
Sensors 2022, 22(19), 7652; https://doi.org/10.3390/s22197652 - 09 Oct 2022
Cited by 3 | Viewed by 1759
Abstract
An optical strain gauge based on a balloon-like interferometer structure formed by a bent standard single-mode fiber combined with a 3D printer piece has been presented and demonstrated, which can be used to measure displacement. The interferometer has a simple and compact size, [...] Read more.
An optical strain gauge based on a balloon-like interferometer structure formed by a bent standard single-mode fiber combined with a 3D printer piece has been presented and demonstrated, which can be used to measure displacement. The interferometer has a simple and compact size, easy fabrication, low cost, and is repeatable. The sensor is based on the interference between the core and cladding modes. This is caused by the fiber’s curvature because when light propagates through the curved balloon-shaped interferometer region, a portion of it will be released from the core limitation and coupled to the cladding. The balloon has an axial displacement as a result of how the artwork was constructed. The sensor head is sandwiched between two cantilevers such that when there is a displacement, the dimension associated with the micro bend is altered. The sensor response as a function of displacement can be determined using wavelength shift or intensity change interrogation techniques. Therefore, this optical strain gauge is a good option for applications where structure displacement needs to be examined. The sensor presents a sensitivity of 55.014 nm for displacement measurements ranging from 0 to 10 mm and a strain sensitivity of 500.13 pm/μϵ. Full article
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18 pages, 4535 KiB  
Article
Optimization of Au:CuO Thin Films by Plasma Surface Modification for High-Resolution LSPR Gas Sensing at Room Temperature
by Manuela Proença, Marco S. Rodrigues, Diana I. Meira, M. Cidalia R. Castro, Pedro V. Rodrigues, Ana V. Machado, Eduardo Alves, Nuno P. Barradas, Joel Borges and Filipe Vaz
Sensors 2022, 22(18), 7043; https://doi.org/10.3390/s22187043 - 17 Sep 2022
Cited by 6 | Viewed by 1765
Abstract
In this study, thin films composed of gold nanoparticles embedded in a copper oxide matrix (Au:CuO), manifesting Localized Surface Plasmon Resonance (LSPR) behavior, were produced by reactive DC magnetron sputtering and post-deposition in-air annealing. The effect of low-power Ar plasma etching on the [...] Read more.
In this study, thin films composed of gold nanoparticles embedded in a copper oxide matrix (Au:CuO), manifesting Localized Surface Plasmon Resonance (LSPR) behavior, were produced by reactive DC magnetron sputtering and post-deposition in-air annealing. The effect of low-power Ar plasma etching on the surface properties of the plasmonic thin films was studied, envisaging its optimization as gas sensors. Thus, this work pretends to attain the maximum sensing response of the thin film system and to demonstrate its potential as a gas sensor. The results show that as Ar plasma treatment time increases, the host CuO matrix is etched while Au nanoparticles are uncovered, which leads to an enhancement of the sensitivity until a certain limit. Above such a time limit for plasma treatment, the CuO bonds are broken, and oxygen is removed from the film’s surface, resulting in a decrease in the gas sensing capabilities. Hence, the importance of the host matrix for the design of the LSPR sensor is also demonstrated. CuO not only provides stability and protection to the Au NPs but also promotes interactions between the thin film’s surface and the tested gases, thereby improving the nanocomposite film’s sensitivity. The optimized sensor sensitivity was estimated at 849 nm/RIU, which demonstrates that the Au-CuO thin films have the potential to be used as an LSPR platform for gas sensors. Full article
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25 pages, 6074 KiB  
Article
Development of Capacitive-Type Sensors by Electrochemical Anodization: Humidity and Touch Sensing Applications
by Joaquim O. Carneiro, Artur Ribeiro, Filipe Miranda, Iran Rocha Segundo, Salmon Landi, Jr., Vasco Teixeira and Manuel F. M. Costa
Sensors 2021, 21(21), 7317; https://doi.org/10.3390/s21217317 - 03 Nov 2021
Cited by 3 | Viewed by 2010
Abstract
This work describes the development of a capacitive-type sensor created from nanoporous anodic aluminium oxide (NP-AAO) prepared by the one-step anodization method conducted in potentiostatic mode and performed in a low-cost homemade system. A series of samples were prepared via an anodization campaign [...] Read more.
This work describes the development of a capacitive-type sensor created from nanoporous anodic aluminium oxide (NP-AAO) prepared by the one-step anodization method conducted in potentiostatic mode and performed in a low-cost homemade system. A series of samples were prepared via an anodization campaign carried out on different acid electrolytes, in which the anodization parameters were adjusted to investigate the effect of pore size and porosity on the capacitive sensing performance. Two sensor test cases are investigated. The first case explores the use of highly uniform NP-AAO structures for humidity sensing applications while the second analyses the use of NP-AAO as a capacitive touch sensor for biological applications, namely, to detect the presence of small “objects” such as bacterial colonies of Escherichia Coli. A mathematical model based on equivalent electrical circuits was developed to evaluate the effect of humidity condensation (inside the pores) on the sensor capacitance and also to estimate the capacitance change of the sensor due to pore blocking by the presence of a certain number of bacterial microorganisms. Regarding the humidity sensing test cases, it was found that the sensitivity of the sensor fabricated in a phosphoric acid solution reaches up to 39 (pF/RH%), which is almost three times higher than the sensor fabricated in oxalic acid and about eight times higher than the sensor fabricated in sulfuric acid. Its improved sensitivity is explained in terms of the pore size effect on the mean free path and the loss of Brownian energy of the water vapour molecules. Concerning the touch sensing test case, it is demonstrated that the NP-AAO structures can be used as capacitive touch sensors because the magnitude of the capacitance change directly depends on the number of bacteria that cover the nanopores; the fraction of the electrode area activated by bacterial pore blocking is about 4.4% and 30.2% for B1 (E. Coli OD600nm = 0.1) and B2 (E. Coli OD600nm = 1) sensors, respectively. Full article
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