Optics

17 pages, 7486 KiB

Open AccessArticle

Synthesis, Optical Properties and Photocatalytic Testing of Sol–Gel TiO₂-Fe₂O₃/PVP Nanopowders

by Stefani Petrova, Yoanna Kostova, Martin Tsvetkov, Angelina Stoyanova, Hristina Hitkova, Polya Marinovska and Albena Bachvarova-Nedelcheva

Optics 2025, 6(2), 22; https://doi.org/10.3390/opt6020022 - 26 May 2025

Viewed by 49

Abstract

In this study, TiO₂-Fe₂O₃/polyvinylpyrrolidone (PVP) hybrids were prepared using the sol–gel method. The iron content in the synthesized samples was 10 and 20 wt%. The influence of PVP on the phase transformation, morphology and optical properties of [...] Read more.

In this study, TiO₂-Fe₂O₃/polyvinylpyrrolidone (PVP) hybrids were prepared using the sol–gel method. The iron content in the synthesized samples was 10 and 20 wt%. The influence of PVP on the phase transformation, morphology and optical properties of the as-prepared hybrids was characterized by various physicochemical methods—XRD analysis, UV–Vis spectroscopy, IR spectroscopy and SEM. The obtained sol–gel powders were tested for photocatalytic activity against tetracycline hydrochloride in distilled water under ultraviolet and simulated solar light illumination. The obtained results were compared to commercial TiO₂ P25 (Evonik). The investigated samples exhibited good photocatalytic efficiency for the degradation of tetracycline hydrochloride; however, better activity was demonstrated by the 90TiO₂-10Fe₂O₃/PVP sample. The latter one displayed weak antibacterial action against E. coli ATCC 25922 in the presence of UVA light. Full article

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25 pages, 2014 KiB

Open AccessArticle

Photoelastic Refractive Index Changes in GaAs Investigated by Finite Element Method (FEM) Simulations

by Daniel T. Cassidy

Optics 2025, 6(2), 21; https://doi.org/10.3390/opt6020021 - 18 May 2025

Viewed by 162

Abstract

Changes in the refractive indices of a GaAs laser chip owing to bonding strain are investigated by two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) simulations. The strain induced by die attach (i.e., the bonding strain) was estimated by fitting simulations to [...] Read more.

Changes in the refractive indices of a GaAs laser chip owing to bonding strain are investigated by two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) simulations. The strain induced by die attach (i.e., the bonding strain) was estimated by fitting simulations to the measured degree of polarisation (DOP) of photoluminescence from the facet of the bonded chip. Changes in the refractive indices were estimated using the strains obtained from fits to DOP data. Differences between the 2D and 3D FEM estimations of the deformation and of the photo-elastic effect are noted. It is recommended that 2D FEM simulations be used as starting points for 3D FEM simulations. Elastic constants for GaAs in plane-of-the-facet coordinate systems for 2D (plane stress and plane strain) and 3D FEM simulations are given. Full article

(This article belongs to the Section Engineering Optics)

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7 pages, 3926 KiB

Open AccessArticle

Infrared Imaging of Photochromic Contrast in Thiazolothiazole-Embedded Polymer Films

by Nuren Z. Shuchi, Tyler J. Adams, Naz F. Tumpa, Dustin Louisos, Glenn D. Boreman, Michael G. Walter and Tino Hofmann

Optics 2025, 6(2), 20; https://doi.org/10.3390/opt6020020 - 16 May 2025

Viewed by 125

Abstract

The increasing demand for optical technologies with dynamic spectral control has driven interest in chromogenic materials, particularly for applications in tunable infrared metasurfaces. Phase-change materials such as vanadium dioxide and germanium–antimony–tellurium, for instance, have been widely used in the infrared regime. However, their [...] Read more.

The increasing demand for optical technologies with dynamic spectral control has driven interest in chromogenic materials, particularly for applications in tunable infrared metasurfaces. Phase-change materials such as vanadium dioxide and germanium–antimony–tellurium, for instance, have been widely used in the infrared regime. However, their reliance on thermal and electrical tuning introduces challenges such as high power consumption, limited emissivity tuning, and slow modulation speeds. Photochromic materials may offer an alternative approach to dynamic infrared metasurfaces, potentially overcoming these limitations through rapid, light-induced changes in their optical properties. This manuscript explores the potential of thiazolothiazole-embedded polymers, known for their reversible photochromic transitions and strong infrared absorption changes, for use in tunable infrared metasurfaces. The material exhibits low absorption and a strong photochromic contrast in the spectral range from 1500

{cm}^{- 1}

to 1700

{cm}^{- 1}

, making it suitable for dynamic infrared light control. This manuscript reports on infrared imaging experiments demonstrating the photochromic contrast in thiazolothiazole-embedded polymer, and thereby provides compelling evidence for its potential applications in dynamic infrared metasurfaces. Full article

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14 pages, 2896 KiB

Open AccessArticle

Optical Design of a Smart-Pixel-Based Optical Convolutional Neural Network

by Young-Gu Ju

Optics 2025, 6(2), 19; https://doi.org/10.3390/opt6020019 - 13 May 2025

Viewed by 156

Abstract

We designed lens systems for a smart-pixel-based optical convolutional neural network (SPOCNN) using optical software to analyze image spread and estimate alignment tolerance for various kernel sizes. The design, based on a three-element lens, was reoptimized to minimize spot size while meeting system [...] Read more.

We designed lens systems for a smart-pixel-based optical convolutional neural network (SPOCNN) using optical software to analyze image spread and estimate alignment tolerance for various kernel sizes. The design, based on a three-element lens, was reoptimized to minimize spot size while meeting system constraints. Simulations included root mean square spot and encircled energy diagrams, showing that geometric aberration increases with the scale factor, while diffraction effect remains constant. Alignment tolerance was determined by combining geometric image size with image spread analysis. While the preliminary scaling analysis predicted a limit at a kernel array size of 66 × 66, simulations showed that a size of 61 × 61 maintains sufficient alignment tolerance, well above the critical threshold. The discrepancy is likely due to lower angular aberration in the simulated optical design. This study confirms that an array size of 61 × 61 is feasible for SPOCNN, validating the scaling analysis for predicting image spread trends caused by aberration and diffraction. Full article

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11 pages, 2946 KiB

Open AccessArticle

Intraocular Pressure Damping by Corneal Elasticity and Viscosity Modulation Using Silicone Hydrogel Soft Contact Lenses

by Francisco J. Ávila

Optics 2025, 6(2), 18; https://doi.org/10.3390/opt6020018 - 9 May 2025

Viewed by 342

Abstract

The biomechanical and optical properties of the cornea are responsible for its functional response, structural integrity and refractive function. Corneal viscoelasticity is the cornea’s ability to absorb transient increases in intraocular pressure (IOP) and constitutes a biomarker of glaucoma. The use of silicone [...] Read more.

The biomechanical and optical properties of the cornea are responsible for its functional response, structural integrity and refractive function. Corneal viscoelasticity is the cornea’s ability to absorb transient increases in intraocular pressure (IOP) and constitutes a biomarker of glaucoma. The use of silicone hydrogel soft contact lenses (SiH-SCLs) can affect both corneal viscoelasticity and IOP. However, the behavior of the pure elastic and viscous components remains hidden within viscoelastic properties, and their influence and relationship with IOP in the biomechanical changes observed with short-term SiH-SCL use remains unknown. This study investigates the effects of silicone hydrogel soft contact lenses (SiH-SCLs) on corneal elasticity and viscosity and their influence on IOP over different lens wear periods: 10 or 20 consecutive days. Ocular Response Analyzer (ORA) measurements were combined with a biomechanical Standard Linear Solid Model (SLSM) to differentiate and calculate the elastic and viscous components of the cornea. The results showed that after 10 days of lens wear, elasticity and viscosity increased, with a significant reduction in IOP. After 20 days, elasticity and viscosity decreased, with a further reduction in IOP, reflecting a time-dependent effect of SiH-SCLs on corneal biomechanics. The study indicates the potential protective role of corneal viscosity against changes in IOP, which may be used for glaucoma treatment. Full article

(This article belongs to the Section Biomedical Optics)

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10 pages, 1800 KiB

Open AccessArticle

Automatic Focusing of Off-Axis Digital Holographic Microscopy by Combining the Discrete Cosine Transform Sparse Dictionary with the Edge Preservation Index

by Zhaoliang Liu, Peizhen Qiu and Yupei Zhang

Optics 2025, 6(2), 17; https://doi.org/10.3390/opt6020017 - 6 May 2025

Viewed by 204

Abstract

Automatic focusing is a crucial research issue for achieving high-quality reconstructed images in digital holographic microscopy. This paper proposes an automatic focusing method that combines the discrete cosine transform (DCT) sparse dictionary with edge preservation index (EPI) criteria for off-axis digital holographic microscopy. [...] Read more.

Automatic focusing is a crucial research issue for achieving high-quality reconstructed images in digital holographic microscopy. This paper proposes an automatic focusing method that combines the discrete cosine transform (DCT) sparse dictionary with edge preservation index (EPI) criteria for off-axis digital holographic microscopy. Specifically, within a predefined search range, Fresnel transform is utilized to reconstruct the off-axis digital hologram, yielding reconstruction images at various reconstruction distances. Synchronously, the DCT sparse dictionary is employed to reduce speckle noise, and the EPI is calculated between the denoised image and original image. The value of EPI is used as an indicator for assessing the focal position. A single-peak focusing curve is obtained within the search range 10 mm, with a step size of 0.1 mm. Once the optimal focus position is determined, a focused and noise-reduced reconstructed image can be simultaneously achieved. Full article

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16 pages, 16987 KiB

Open AccessArticle

Comparative Molecular Dynamics Study of Graphitization Mechanisms in Nanosecond Laser Irradiation of Single-Crystal and Nanocrystalline Diamond

by Huixin Yuan, Liang Zhao, Weimian Guan, Yuqi Yang and Junjie Zhang

Optics 2025, 6(2), 16; https://doi.org/10.3390/opt6020016 - 25 Apr 2025

Viewed by 251

Abstract

The mechanisms of material removal and structural transformation under laser radiation differ significantly between single-crystal diamond (SCD) and nanocrystalline diamond (NCD). This study employs atomic simulations to investigate the material removal mechanisms and structural transformation behaviors of SCD and NCD when subjected to [...] Read more.

The mechanisms of material removal and structural transformation under laser radiation differ significantly between single-crystal diamond (SCD) and nanocrystalline diamond (NCD). This study employs atomic simulations to investigate the material removal mechanisms and structural transformation behaviors of SCD and NCD when subjected to laser irradiation. We analyze the effects of temperature and stress changes induced by laser radiation on structural transformations, revealing the driving mechanism behind graphitization transitions. Specifically, the thermal–mechanical coupling effect induced by lasers leads to graphitization in SCD, while in NCD, due to the stress concentration effects at the grain boundaries, graphitization preferentially occurs at these boundaries. The material removal processes for both SCD and NCD are attributed to thermal stress concentrations in the regions where the laser interacts with the diamond surface. This investigation provides a theoretical foundation for a more profound understanding of the behavior of diamond materials during laser irradiation. Full article

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15 pages, 7817 KiB

Open AccessArticle

Sparsity-Guided Phase Retrieval to Handle Concave- and Convex-Shaped Specimens in Inline Holography, Taking the Complexity Parameter into Account

by Yao Koffi, Jocelyne M. Bosson, Marius Ipo Gnetto and Jeremie T. Zoueu

Optics 2025, 6(2), 15; https://doi.org/10.3390/opt6020015 - 17 Apr 2025

Viewed by 314

Abstract

In this work, we explore an optimization idea for the complexity guidance of a phase retrieval solution for a single acquired hologram. This method associates free-space backpropagation with the fast iterative shrinkage-thresholding algorithm (FISTA), which incorporates an improvement in the total variation (TV) [...] Read more.

In this work, we explore an optimization idea for the complexity guidance of a phase retrieval solution for a single acquired hologram. This method associates free-space backpropagation with the fast iterative shrinkage-thresholding algorithm (FISTA), which incorporates an improvement in the total variation (TV) to guide the complexity of the phase retrieval solution from the complex diffracted field measurement. The developed procedure can provide excellent phase reconstruction using only a single acquired hologram. Full article

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13 pages, 2979 KiB

Open AccessArticle

Growth and Properties of (Yb-Er) Co-Doped ZnO Thin Films Deposited via Spray Pyrolysis Technique

by Abderrahim El Hat, Imane Chaki, Rida Essajai, Abdelmajid Fakhim Lamrani, Boubker Fares, Mohammed Regragui, Aziz Dinia and Mohammed Abd-Lefdil

Optics 2025, 6(2), 14; https://doi.org/10.3390/opt6020014 - 3 Apr 2025

Viewed by 429

Abstract

Yb_xEr_yZnO thin films with a low concentration (x = 5%, y = 0, 1, 3%) were made on glass substrates using the spray pyrolysis method. The films were characterized through the use of specific techniques to investigate their structural, [...] Read more.

Yb_xEr_yZnO thin films with a low concentration (x = 5%, y = 0, 1, 3%) were made on glass substrates using the spray pyrolysis method. The films were characterized through the use of specific techniques to investigate their structural, optical, and electrical properties. The XRD structural analysis of the films revealed that they are polycrystalline with a hexagonal wurtzite structure and a preferential orientation in the (002) direction. The optical characterization of the co-doped layers in the range of 200 to 800 nm revealed that co-doping had a significant impact on the values of transmission. A well-defined peak in the infrared domain centered around 980 nm was observed in photoluminescence measurements. This peak signifies the transition between the electronic levels ²F_5/2 (ground state) and ²F_7/2 (excited state), proving that photons are efficiently transferred between the ZnO matrix and the Yb³⁺ ion. All layers exhibited n-type conduction and an electrical resistivity decrease to 6.0 × 10⁻² Ω cm according to Hall effect measurements at room temperature. Full article

(This article belongs to the Special Issue Optoelectronic Thin Films)

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15 pages, 5132 KiB

Open AccessArticle

Theoretical Model of Curved Liquid Surface in the Microholes for Molding Microlenses

by Yuyang Shi, Yan Long, Xuhui Zhang, Li Wei, Bo Dai and Dawei Zhang

Optics 2025, 6(2), 13; https://doi.org/10.3390/opt6020013 - 3 Apr 2025

Viewed by 335

Abstract

Microlenses are essential optics widely used in many fields. The microfluidics-assisted fabrication method provides a rapid, convenient way to manufacture microlenses. However, there is no mathematical model to describe the profile of the liquid surface. This paper provides a theoretical explanation and mathematical [...] Read more.

Microlenses are essential optics widely used in many fields. The microfluidics-assisted fabrication method provides a rapid, convenient way to manufacture microlenses. However, there is no mathematical model to describe the profile of the liquid surface. This paper provides a theoretical explanation and mathematical model for the formation of the liquid surface of different curvatures in the microholes of different shapes. A numerical model based on the finite–difference time–domain method verifies the mathematical model. Furthermore, the optical properties of the microlenses in different shapes are analyzed through the demolded microlenses. The proposed theoretical model provides an analytical way to study the properties of microlenses. Full article

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8 pages, 1345 KiB

Open AccessArticle

High-Myopia Diagnosis by Reciprocal of Circle Radius in Choroidal Image

by Shuo-Tsung Chen, Ren-Jie Ye, Ching-Fu Chen, Keng-Yuan Chang, Yu-Hung Huang, Sheng-Jie Tseng and Jun-Qi Liu

Optics 2025, 6(2), 12; https://doi.org/10.3390/opt6020012 - 1 Apr 2025

Cited by 1 | Viewed by 327

Abstract

Light-emitting electronic devices are widely used at present, and this increases the risk of myopia. Thus, the early identification of myopia and the prevention of further exacerbation has become an essential issue in ophthalmology. Recently, choroidal imaging has been used to assist in [...] Read more.

Light-emitting electronic devices are widely used at present, and this increases the risk of myopia. Thus, the early identification of myopia and the prevention of further exacerbation has become an essential issue in ophthalmology. Recently, choroidal imaging has been used to assist in the early identification and prevention of high myopia due to the fact that swept-source optical coherence tomography (SS-OCT) is an essential diagnostic tool in ophthalmology. This study presents a novel method to judge high myopia using the SS-OCT image dataset obtained from a university hospital. In order to relate the proposed method to the region of the SS-OCT image, the curvature analysis of an arbitrary segmented curve similar to the region of the SS-OCT is first illustrated by quadratic functions and matrix operations. Next, the curvature formula is derived and then applied to the choroidal curve obtained manually in each patient’s choroidal image. In particular, we applied the curvature analysis and its results to find the maximal curvature and average curvature of each patient’s choroidal curve. Finally, we used the maximal curvature and average curvature to evaluate high myopia. The accuracy of the proposed maximal curvature method and average curvature method in the experimental results to verify the proposed method. Full article

(This article belongs to the Special Issue Advanced Optical Imaging for Biomedicine)

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