Photonics

Open AccessArticle

Remote Operation of an Open-Path, Laser-Based Instrument for Atmospheric CO₂ and CH₄ Monitoring

by

Panagiotis Siozos

,

Giannis Psyllakis

and

Michalis Velegrakis

Photonics 2023, 10(4), 386; https://doi.org/10.3390/photonics10040386 - 31 Mar 2023

Abstract

The technical specifications and the evaluation of the remote operation of the open-path, tunable diode laser absorption spectroscopic (TDLAS) instrument are presented. The instrument is equipped with two low optical power diode lasers in the near-infrared spectral range for the atmospheric detection of [...] Read more.

The technical specifications and the evaluation of the remote operation of the open-path, tunable diode laser absorption spectroscopic (TDLAS) instrument are presented. The instrument is equipped with two low optical power diode lasers in the near-infrared spectral range for the atmospheric detection of carbon dioxide, methane, and water vapors (CO₂, CH_4, and H₂O). Additionally, the instrument eliminates the requirement of retroreflectors since it detects the back reflection of the laser beam from any topographic target. The instrument was operated remotely by measuring background concentrations of CO₂ and CH₄ in the atmosphere from 24 November 2022 to 4 January 2023. The accuracy of CO₂ and CH₄ measurement retrievals on a 200 m laser path was estimated at 20 ppm (4.8%) and 60 ppb (3.1%), respectively. The CH₄ accuracy is comparable, but the CO₂ accuracy is noticeably lower than the accuracy achieved in local operation. The accuracy issues raised are studied and discussed in terms of the laser driver’s cooling performance. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Photonics Sensors)

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Open AccessArticle

Optical Design of a Slitless Astronomical Spectrograph with a Composite Holographic Grism

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Photonics 2023, 10(4), 385; https://doi.org/10.3390/photonics10040385 - 31 Mar 2023

Abstract

In the present work, we consider an optical design of a slitless spectrograph for an existing 0.5 m-class telescope. This design concept has a number of advantages such as compact size, simplicity, and simultaneous coverage of a large field of view. A challenge [...] Read more.

In the present work, we consider an optical design of a slitless spectrograph for an existing 0.5 m-class telescope. This design concept has a number of advantages such as compact size, simplicity, and simultaneous coverage of a large field of view. A challenge with this design is correcting aberrations caused by placing a dispersing element in a converging beam. To overcome this issue, we propose to use a composite grism, which represents a combination of a prism and a volume-phase holographic grating, the latter which is split into zones with independently optimized parameters. We demonstrate two designs of such a grism. In both designs, the spectrograph operates in the range of 450–950 nm in an

F / 6.8

beam and covers a field of view of 35.6

^{'}

× 7.2

^{'}

. Through advanced modeling, it is shown that a composite grism having four rectangular zones with different thickness and index modulation depth of the hologram and recorded with an auxiliary deformable mirror decreases the astigmatic elongation by a factor of 85, increases the spectral resolving power by 4.4 times, and reaches

R 1389

while increasing the average diffraction efficiency by a factor of

1.31

. If we reduce the number of zones to only two, replace the deformable mirror with two static corrector plates, and fix the hologram thickness, the corresponding performance gains still remain high: the astigmatism is reduced by a factor of 61, the spectral resolving power is up to

1.7

times higher, reaching

R 1067

, and the efficiency is increased by a factor of

1.27

. This shows that the proposed design allows the construction of a simple and compact instrument, providing high performance over the entire field of view and spectral range. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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Open AccessArticle

Plasmonic Nanostructuring by Means of Industrial-Friendly Laser Techniques

by

Dimitrios Ntemogiannis

,

Panagiotis Floropoulos

,

Vagelis Karoutsos

,

Spyridon Grammatikopoulos

,

Panagiotis Poulopoulos

and

Dimitris Alexandropoulos

Photonics 2023, 10(4), 384; https://doi.org/10.3390/photonics10040384 - 30 Mar 2023

Abstract

The continuously growing demand for functional plasmonic devices or systems urges the implementation of economical and accelerated nanostructuring techniques. Laser annealing represents a promising approach to address this challenge, given its widespread usage in industry and research, as well as its unique advantages. [...] Read more.

The continuously growing demand for functional plasmonic devices or systems urges the implementation of economical and accelerated nanostructuring techniques. Laser annealing represents a promising approach to address this challenge, given its widespread usage in industry and research, as well as its unique advantages. This study proposes a scalable, rapid, versatile, and cost-efficient method to grow self-assembled nanostructures on metallic ultrathin films and multilayers, with high precision and patterning freedom. By employing industrial-grade equipment, specifically a 1070 nm nanosecond fiber laser and magnetron sputtering system, we directly grew self-assembled nanoparticles on Ag ultrathin films and AgPd multilayers deposited on Corning glass, via laser annealing at ambient conditions. The self-assembled nanoparticles were formed in designated areas by varying several laser parameters and exhibited intense localized surface plasmon resonances. Optical and structural characterization were realized via UV–Vis spectroscopy and atomic force microscopy, respectively. The plasmonic characteristics were found to depend on the initial film thickness and laser annealing parameters. Laser-treated films exhibited remarkable plasmonic behavior, demonstrating that this method does not lack nanostructuring quality while offering scalability and practicality. Further optimization of the laser settings can refine the process and result in an even faster, cheaper, and more qualitative nanostructuring method. Full article

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Open AccessCommunication

Study on Temperature and Water Turbulence Impact on Saline Water-Based Wireless Optical Communication

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Photonics 2023, 10(4), 383; https://doi.org/10.3390/photonics10040383 - 30 Mar 2023

Abstract

Underwater wireless optical communication (UWOC) is a promising solution for Gb/s rate and long-distance underwater communication. However, random changes in the local temperature and salinity of seawater have caused different refractive indices of ocean water. This study investigated the UWOC system in different [...] Read more.

Underwater wireless optical communication (UWOC) is a promising solution for Gb/s rate and long-distance underwater communication. However, random changes in the local temperature and salinity of seawater have caused different refractive indices of ocean water. This study investigated the UWOC system in different saline water while simultaneously changing the temperature and water flow. A maximum bit error rate (BER) of 4.851 × 10⁻⁶ was measured at −7.41 dBm in 3 m of 45.56 g/L saline water. By changing the temperature to 30 °C, the bit error rate (BER) value reached 5.12 × 10⁻⁶ in the saline water. On the other hand, water flow was generated in various types of water salinity to compare simultaneous environmental effects in the UWOC system. In 45.56 g/L of saline water with water flow, the UWOC system was still capable of reaching a BER value of 4 × 10⁻⁴. Full article

(This article belongs to the Special Issue Women’s Special Issue Series: Photonics)

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Open AccessCommunication

Design of Full Stokes Vector Polarimetry Based on Metasurfaces for Wide-Angle Incident Light

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Photonics 2023, 10(4), 382; https://doi.org/10.3390/photonics10040382 - 30 Mar 2023

Abstract

Polarization measurement plays an important role in optical detection, communication, and imaging systems. Compact polarimetry with a wide angle of incident light will break the restrictions of the limited incident angle and improve its practicality. In this paper, a full Stokes vector polarimetry [...] Read more.

Polarization measurement plays an important role in optical detection, communication, and imaging systems. Compact polarimetry with a wide angle of incident light will break the restrictions of the limited incident angle and improve its practicality. In this paper, a full Stokes vector polarimetry with a wide incident angle of ±20°, based on a two-dimensional metasurface, is proposed. According to the simulation results, the maximum measurement error of the Stokes vector at 20° oblique incidence is 0.09. The light transmittance of the proposed structure is higher than 83%. Moreover, the tilt angle of the incident light can be determined with a calculation error lower than 0.5°, according to the focusing position of the transmitted light on the focal plane. The operating wavelength of the proposed polarimetry is set to 530 nm of green light, which makes it a potential application in visible light communication and underwater optical systems. Full article

(This article belongs to the Special Issue Metasurface Diffraction and Polarization Optics)

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Open AccessArticle

Changes in Wavefront Error of the Eye for Different Accommodation Targets under the Application of Phenylephrine Hydrochloride

by

María Mechó-García

,

Iñaki Blanco-Martínez

,

Paulo Fernandes

,

Rute J. Macedo-de-Araújo

,

Miguel Faria-Ribeiro

and

José Manuel González-Méijome

Photonics 2023, 10(4), 381; https://doi.org/10.3390/photonics10040381 - 30 Mar 2023

Abstract

Pharmacological dilation of the eye to have a larger pupil diameter may allow a better understanding of the wavefront error changes with accommodation. This work aimed to investigate whether dilation of the pupil with Phenylephrine Hydrochloride (PHCl) application changes the accommodative response and [...] Read more.

Pharmacological dilation of the eye to have a larger pupil diameter may allow a better understanding of the wavefront error changes with accommodation. This work aimed to investigate whether dilation of the pupil with Phenylephrine Hydrochloride (PHCl) application changes the accommodative response and the Zernike coefficient magnitude with accommodative demand when computed to a common pupil size. Sixteen right eyes of healthy young subjects were measured with the commercial Hartmann–Shack aberrometer IRX3 (Imagine Eyes, Orsay, France) 30 min after two drops of 1.0% PHCl were applied. The eye wavefronts for accommodative demands from 0 to 5 D were measured in natural conditions and after pupil dilatation. Statistically significant differences between both conditions were found for the Zernike coefficients

C_{3}^{- 1}

,

C_{3}^{1},

C_{4}^{0}

and

C_{6}^{0}

. Without the effect of PHCl, higher values were found for all higher-order Zernike coefficients (HOA). With increased accommodative response, an increase of

C_{3}^{- 1}

and a decrease of

C_{3}^{1}

was observed and the

C_{4}^{0}

becomes more negative; the change from positive to negative is shown in the accommodative demand of 1.5 D. Conversely,

C_{6}^{0}

increases with increasing accommodative demand. To conclude, the results demonstrated that the mydriatic effect of PHCl causes changes in the magnitude of HOA when accommodation is stimulated. The trends observed in the different Zernike coefficients were the same reported in previous studies. Full article

(This article belongs to the Special Issue Visual Optics)

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Open AccessArticle

Dynamics of the Femtosecond Mid-IR Laser Pulse Impact on a Bulk Silicon

by

Evgenii Mareev

,

Nikolay Obydennov

and

Fedor Potemkin

Photonics 2023, 10(4), 380; https://doi.org/10.3390/photonics10040380 - 30 Mar 2023

Abstract

In this study, we reconstructed the dynamics of the impact of mid-IR-range (4.6 μm) femtosecond laser pulses on bulk silicon under tight focusing conditions (NA = 0.5). Our experimental results show that under this impact, the deposited energy density (DED) reaches approximately 4 [...] Read more.

In this study, we reconstructed the dynamics of the impact of mid-IR-range (4.6 μm) femtosecond laser pulses on bulk silicon under tight focusing conditions (NA = 0.5). Our experimental results show that under this impact, the deposited energy density (DED) reaches approximately 4 kJ/cm³ (at an energy slightly above the plasma-formation threshold). Initially, the femtosecond pulse energy is absorbed by the laser-induced plasma, with a lifetime of approximately 160–320 fs (depending on the laser pulse energy). The energy transfer from the plasma to the atomic subsystem occurs on a sub-ps timescale, which generates a shock wave and excites coherent phonons on a sub-ps scale. The shift of atoms in the lattice at the front of the shock wave results in a cascade of phase transitions (Si-X => Si-VII => Si-VI => Si-XI => Si-II), leading to a change in the phonon spectra of silicon. Full article

(This article belongs to the Special Issue Ultrafast Laser Systems)

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Open AccessArticle

An Interlayer of Ultrasmall N-Rich Carbon Dots for Optimization of SnO₂/CsFAPbI₃ Interface

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Aleksandra V. Koroleva

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Photonics 2023, 10(4), 379; https://doi.org/10.3390/photonics10040379 - 30 Mar 2023

Abstract

Photovoltaic devices based on organic–inorganic hybrid perovskites have engaged tremendous attention due to the enormous increase in power conversion efficiency (PCE). However, defect states formed at grain boundaries and interfaces hinder the achievement of PCE. A prospective strategy to both reduce interfacial defects [...] Read more.

Photovoltaic devices based on organic–inorganic hybrid perovskites have engaged tremendous attention due to the enormous increase in power conversion efficiency (PCE). However, defect states formed at grain boundaries and interfaces hinder the achievement of PCE. A prospective strategy to both reduce interfacial defects and control perovskite growth is the passivation of interfaces. The passivation of the electron-transporting layer/perovskite interface with ultrasmall carbon dots (CDs) with suitable chemical composition and functional groups on their surface may simultaneously affect the morphology of a perovskite layer, facilitate charge carriers extraction, and suppress interfacial recombination. Here, we show that CDs synthesized from diamine precursors may be used as an interlayer at the SnO₂/FACsPbI₃ interface. Ultrasmall CDs form a smooth, thin layer, providing better perovskite layer morphology. CD interlayers result in an increased average perovskite grain size, suppress the formation of small grains, and improve charge carriers’ extraction. As a result, photovoltaic devices with CD interlayers demonstrate a higher PCE due to the increased short-circuit current density and fill factor. These findings provide further insight into the construction of interfaces based on carbon nanomaterials. Full article

(This article belongs to the Special Issue Recent Progress in Solar Cell Technology and Future Prospects)

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Open AccessCommunication

Fiber-Fed 3D Printing of Germanate Glass Optics

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Photonics 2023, 10(4), 378; https://doi.org/10.3390/photonics10040378 - 29 Mar 2023

Abstract

In recent years, 3D printing glass optics has gained massive attention in industry and academia since glass could be an ideal material to make optical elements, including the lens. However, the limitation of materials and printing methods has prevented 3D printing glass optics [...] Read more.

In recent years, 3D printing glass optics has gained massive attention in industry and academia since glass could be an ideal material to make optical elements, including the lens. However, the limitation of materials and printing methods has prevented 3D printing glass optics progress. Therefore, we have developed a novel printing strategy for germanate glass printing instead of pure silica. Moreover, compared with traditional multi-component quartz glass, germanate glass has unmatched advantages for its mid-infrared (MIR) transparency and outstanding visible light imaging performance. Furthermore, compared with non-oxide glass (fluoride glass and chalcogenide glass), germanate glass has much better mechanical, physical, and chemical properties and a high refractive index. Germanate glass has been widely applied in remote sensing, ranging, environmental detection, and biomedical detection. However, it is difficult to shape, cast, polish, and grind for optical and photonics applications such as imaging optics and laser-collimation optics. These drawbacks have made germanate glass inaccessible to complex optical elements and greatly increased their cost. In this report, we use germanate glass fibers with a diameter of 125 µm based on fiber-fed laser heating technology to fabricate an mm-size optical application. In this paper, we combine the fiber-fed laser heating technology with an optimized temperature control process to manufacture high-precision optical elements. Germanate glass optics can be printed with excellent visible light and IR transparency and a smooth surface with roughness under 4 nm. By optimizing the layer-by-layer 3D printing process and the thermal feedback in the printing process, we avoid cracks and minimize surface deformation. This work shows the possibility of the mm-size glass optical elements 3D printing and widens its application for IR optics. Full article

(This article belongs to the Special Issue Direct Laser Writing for Photonic Applications)

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Open AccessFeature PaperArticle

Comparative Performance Analysis of Femtosecond-Laser-Written Diode-Pumped Pr:LiLuF₄ Visible Waveguide Lasers

by

Davide Baiocco

,

Ignacio Lopez-Quintas

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Javier R. Vázquez de Aldana

,

Mauro Tonelli

and

Alessandro Tredicucci

Photonics 2023, 10(4), 377; https://doi.org/10.3390/photonics10040377 - 29 Mar 2023

Abstract

In this work, we present the operation of a femtosecond-laser-written diode-pumped visible waveguide laser based on praseodymium-doped lithium lutetium fluoride. The refractive index modification induced by the femtosecond laser in the crystal exhibits an anisotropic behavior, thus enabling the fabrication of different types [...] Read more.

In this work, we present the operation of a femtosecond-laser-written diode-pumped visible waveguide laser based on praseodymium-doped lithium lutetium fluoride. The refractive index modification induced by the femtosecond laser in the crystal exhibits an anisotropic behavior, thus enabling the fabrication of different types of waveguides from single-track structures to stress-induced waveguides and depressed cladding structures. All the waveguides were characterized by realizing transmission measurements and the waveguide design was optimized to obtain extremely low propagation losses, equal to 0.12

d

B

/

c

m

. Lasing has been achieved at 604

n

m

and 721

n

m

from different waveguides. In addition, stable continuous-wave lasing at 698

n

m

has been obtained in a depressed cladding waveguide. This wavelength corresponds to the one needed for the transition of the atomic clock based on the neutral strontium atom. In the end, we report the observation of laser emission at 645

n

m

from a depressed cladding waveguide. Full article

(This article belongs to the Special Issue Novel Applications of Solid-State Laser and Future Prospects)

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Open AccessArticle

Bandwidth Expansion of Zero-Power-Consumption Visible Light Communication System

by

Yiwu Xu

,

Xiongbin Chen

and

Yufeng Wang

Photonics 2023, 10(4), 376; https://doi.org/10.3390/photonics10040376 - 28 Mar 2023

Abstract

The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of [...] Read more.

The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of the communication system is added between the transmitter and the receiver to equalize the amplitude–frequency response of the solar cell. Based on the measurement of the original amplitude–frequency response of the system, the zero-pole of the predistortion circuit is calculated, and an accurate equalization circuit is designed by using separate components to expand the 3 dB bandwidth of the system. The test results show that the 3 dB bandwidth of the visible light self-powered communication system is increased from 85 kHz to 750 kHz, and the system bandwidth is expanded by nearly 10 times. Full article

(This article belongs to the Special Issue Visible Light Communications)

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Open AccessCommunication

Optical Temperature Sensors Based on Down-Conversion Nd³⁺,Yb³⁺:LiYF₄ Microparticles

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Photonics 2023, 10(4), 375; https://doi.org/10.3390/photonics10040375 - 28 Mar 2023

Abstract

Nd³⁺ (0.3 mol.%), Yb³⁺ (0, 1, 2, 3 and 5 mol.%): LiYF₄ phosphors were grown by the Bridgman–Stockbarger technique. The luminescence intensity ratio (LIR) of Nd³⁺ (⁴F_3/2–⁴I_9/2, ~866 nm) and Yb [...] Read more.

Nd³⁺ (0.3 mol.%), Yb³⁺ (0, 1, 2, 3 and 5 mol.%): LiYF₄ phosphors were grown by the Bridgman–Stockbarger technique. The luminescence intensity ratio (LIR) of Nd³⁺ (⁴F_3/2–⁴I_9/2, ~866 nm) and Yb³⁺ emission (²F_5/2–²F_7/2, ~980 nm) was taken as a parameter. The energy exchange between ⁴F_3/2 (Nd³⁺) and ²F_5/2 (Yb³⁺) occurs via phonons, which elucidates the LIR temperature dependence. The influence of the cross-relaxation process on the temperature sensitivity was estimated as negligible. The LIR function depends on the Yb³⁺ concentration at a fixed 0.3 mol.% Nd³⁺. The maximum S_a and S_r value were reached for Nd³⁺ (0.3%), Yb³⁺ (1.0%): LiYF₄ (S_a = 0.007 K⁻¹ at 320 K) and Nd³⁺ (0.3%), Yb³⁺ (5.0%): LiYF₄ (S_r = 1, 1.03%*K⁻¹ at 260 K), respectively. Full article

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Open AccessArticle

Simulation-Based Considerations on the Rayleigh Criterion in Super-Resolution Techniques Based on Speckle Interferometry

by

Yasuhiko Arai

and

Tong Chen

Photonics 2023, 10(4), 374; https://doi.org/10.3390/photonics10040374 - 28 Mar 2023

Abstract

This study sought to explain the physical phenomenon that eludes the constraints of the Rayleigh criterion in the microstructure observation method using speckle interferometry, for which super-resolution has been experimentally proven; the study was conducted using computer simulations. Separating the light from two [...] Read more.

This study sought to explain the physical phenomenon that eludes the constraints of the Rayleigh criterion in the microstructure observation method using speckle interferometry, for which super-resolution has been experimentally proven; the study was conducted using computer simulations. Separating the light from two light sources in close proximity, which exceeded the Rayleigh criterion under incoherent light, was believed to be impossible. The simulation results, however, showed that when coherent light is used, the separation of two close points is not necessarily impossible if the light phases between the two points are different. Furthermore, the resolution of microstructure observation techniques based on speckle interferometry was discussed. A new interpretation of the Rayleigh criterion in super-resolution techniques based on speckle interferometry was reported. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology)

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Open AccessArticle

Modulation Format Identification and OSNR Monitoring Based on Multi-Feature Fusion Network

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Photonics 2023, 10(4), 373; https://doi.org/10.3390/photonics10040373 - 27 Mar 2023

Abstract

In this paper, we propose a multi-feature fusion network (MFF-Net) for a modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) monitoring scheme. The constellation map data used in this work comes from five modulation formats, namely 56 Gbit/s 4/8 phase shift keying [...] Read more.

In this paper, we propose a multi-feature fusion network (MFF-Net) for a modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) monitoring scheme. The constellation map data used in this work comes from five modulation formats, namely 56 Gbit/s 4/8 phase shift keying (PSK) and 16/32/64 quadrature amplitude modulation (QAM). The constellation maps are input to one branch network of the MFF-Net, and then the constellation maps are processed by horizontal projection and used as input to another branch network as a way to fuse the two image features. The results show that the scheme achieves 100% MFI accuracy and 98.82% OSNR monitoring accuracy for the five modulation formats. In addition, the performance of MFF-Net and binarized convolutional neural network (B-CNN), visual geometry group network (VGG-Net), and traditional weighted multi-task learning (EW-MTL) are compared to present the superiority of the method. The effect of model structure on MFF-Net is also discussed. The robustness of the model is also evaluated for different transmission distances and bit rates. Full article

(This article belongs to the Topic Fiber Optic Communication)

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Open AccessArticle

Effect of Pulsation in Microstructure and Mechanical Properties of Titanium Alloy-Annealed Welded Joints at Different Temperatures

by

Uday Kumar

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Somnath Chattopadhyaya

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Alok Kumar Das

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A. H. Seikh

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Shubham Sharma

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Shashi Prakash Dwivedi

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Photonics 2023, 10(4), 372; https://doi.org/10.3390/photonics10040372 - 27 Mar 2023

Abstract

Thin sheets of Ti-6Al-4V alloy of thickness 1 mm were butt welded using a pulsed Nd-YAG low-power laser setup. The goal of this research is to explore the influence of pulsation on the microstructure and mechanical properties. In addition to that, annealing at [...] Read more.

Thin sheets of Ti-6Al-4V alloy of thickness 1 mm were butt welded using a pulsed Nd-YAG low-power laser setup. The goal of this research is to explore the influence of pulsation on the microstructure and mechanical properties. In addition to that, annealing at different temperatures has been performed to compare the results of pulsation and heat treatment. The results indicate that after annealing at 980 °C, the structure completely transformed into an equiaxed structure. When annealed at 1010 °C, almost the total area is composed of an equiaxed α phase, and the grains are coarse as compared to the previous. This suggests that the grain size becomes thicker when the annealing temperature is raised above 980 °C. The volume fraction of the equiaxed structure is maximum. It can be deduced that the volume–fraction is dependent on the annealing temperature. The volume fraction of the equiaxed structure increases as the annealing temperature increases. A higher tensile strength value of the sample annealed at 980 °C was found as compared with the overlapped sample (A-2). The fusion zone overlapped sample (A-2) shows high hardness with a value of 397 HV₁. In the FZ sample, annealing at 980 °C has a hardness of 386 HV₁. The (A-2) sample indicates higher (3–4%) hardness as compared to the annealed sample at the FZ. The β phase is increased by 16% in the XRD analysis of the overlapped samples. Hence, it is evident that the amount of β phase has increased during heating, and a complete transformation has taken place at a temperature of 958 °C. Full article

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Open AccessArticle

Transverse Electric Guided Wave Propagation in a Plane Waveguide with Kerr Nonlinearity and Perturbed Inhomogeneity in the Permittivity Function

by

Anna Dyundyaeva

,

Stanislav Tikhov

and

Dmitry Valovik

Photonics 2023, 10(4), 371; https://doi.org/10.3390/photonics10040371 - 27 Mar 2023

Abstract

The paper focuses on the problem of transverse electric wave propagation in a plane-shielded waveguide filled with a nonhomogeneous and nonlinear (Kerr) medium. The nonlinear part of the permittivity is characterized by the Kerr law in the focusing regime, while its linear part [...] Read more.

The paper focuses on the problem of transverse electric wave propagation in a plane-shielded waveguide filled with a nonhomogeneous and nonlinear (Kerr) medium. The nonlinear part of the permittivity is characterized by the Kerr law in the focusing regime, while its linear part is a constant that is perturbed by a small continuous function. Such perturbation can be considered to be an attempt to take into account the inevitable presence of impurities in the medium, causing slight deviations in the dielectric permittivity. In the paper, the existence of solutions to the considered problem is proved, including solutions with and without linear counterparts. Some numerical results are presented as well. Full article

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Open AccessCommunication

Key Space Enhancement of Chaos Communication Using Semiconductor Lasers with Spectrum-Programmable Optoelectronic Feedback

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Photonics 2023, 10(4), 370; https://doi.org/10.3390/photonics10040370 - 26 Mar 2023

Abstract

We propose a scheme for key-space-enhanced chaos secure communication using semiconductor lasers with spectrum-programmable optoelectronic feedback. This feedback consists of multiple parallel optoelectronic feedback loops composed of bandpass filters and radio-frequency amplifiers. The centre frequencies of the filters and gain coefficients of the [...] Read more.

We propose a scheme for key-space-enhanced chaos secure communication using semiconductor lasers with spectrum-programmable optoelectronic feedback. This feedback consists of multiple parallel optoelectronic feedback loops composed of bandpass filters and radio-frequency amplifiers. The centre frequencies of the filters and gain coefficients of the amplifiers increase the key space. We use 12 parallel filtered feedback loops to analyse the effects of parameter mismatch on the synchronization quality. The simulation result indicates that the key space reaches approximately 2¹⁰⁰ at a data rate of 10 Gbit/s, and it can be further enhanced by increasing the number of feedback loops. These results suggest an alternative approach for security-enhanced optical chaos communication. Full article

(This article belongs to the Topic Fiber Optic Communication)

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Open AccessCommunication

Feasibility Demonstration of THz Wave Generation/Modulation Based on Photomixing Using a Single Wavelength-Tunable Laser

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Photonics 2023, 10(4), 369; https://doi.org/10.3390/photonics10040369 - 25 Mar 2023

Abstract

The photomixing of two lightwaves is one of the promising methods of generating a terahertz (THz) wave. The conventional photomixing system consisting of two lasers and a modulator results in large transmitter volumes and high power consumption. To solve this issue, we devised [...] Read more.

The photomixing of two lightwaves is one of the promising methods of generating a terahertz (THz) wave. The conventional photomixing system consisting of two lasers and a modulator results in large transmitter volumes and high power consumption. To solve this issue, we devised a novel THz wave generation and modulation system based on photomixing using a single wavelength-tunable laser in combination with delayed self-multiplexing. We successfully demonstrated the feasibility of 300-GHz wave generation and modulation. Full article

(This article belongs to the Topic Applications of Photonics, Laser, Plasma and Radiation Physics)

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Open AccessArticle

Generation, Topological Charge, and Orbital Angular Momentum of Off-Axis Double Vortex Beams

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Photonics 2023, 10(4), 368; https://doi.org/10.3390/photonics10040368 - 25 Mar 2023

Abstract

Compared with the on-axis vortex beam and the off-axis single vortex beam, the off-axis double vortex beam has more control degrees of freedom and brings rich physical properties. In this work, we investigate theoretically and experimentally the generation, topological charge (TC), and orbital [...] Read more.

Compared with the on-axis vortex beam and the off-axis single vortex beam, the off-axis double vortex beam has more control degrees of freedom and brings rich physical properties. In this work, we investigate theoretically and experimentally the generation, topological charge (TC), and orbital angular momentum (OAM) of off-axis double vortex beams. It is demonstrated that the tilted lens method can detect not only the magnitudes and signs of two TCs of the off-axis double vortex beam but also the spatial distribution of the TCs. Moreover, the average OAM value of the off-axis double vortex beam decreases nonlinearly as the off-axis distance increases, although its TC is independent of the off-axis distance of phase singularities. The results indicate that the average OAM of the off-axis double vortex beam can be easily controlled by changing the relative position of two-phase singularities, thereby realizing the applications of multi-degrees of freedom particle manipulation, optical communication, and material processing. Full article

(This article belongs to the Special Issue Advances and Application of Structured Light)

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Photonics

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