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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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18 pages, 2319 KiB  
Article
Propagation of a Partially Coherent Bessel–Gaussian Beam in a Uniform Medium and Turbulent Atmosphere
by Igor Lukin and Vladimir Lukin
Photonics 2024, 11(6), 562; https://doi.org/10.3390/photonics11060562 - 14 Jun 2024
Cited by 1 | Viewed by 2225
Abstract
In this paper, the coherent properties of partially coherent Bessel–Gaussian optical beams propagating through a uniform medium (free space) or a turbulent atmosphere are examined theoretically. The consideration is based on the analytical solution of the equation for the transverse second-order mutual coherence [...] Read more.
In this paper, the coherent properties of partially coherent Bessel–Gaussian optical beams propagating through a uniform medium (free space) or a turbulent atmosphere are examined theoretically. The consideration is based on the analytical solution of the equation for the transverse second-order mutual coherence function of the field of partially coherent optical radiation in a turbulent atmosphere. For the partially coherent Bessel–Gaussian beam, the second-order mutual coherence function of the source field is taken as a Gaussian–Schell model. In this approximation, we analyze the behavior of the coherence degree and the integral coherence scale of these beams as a function of the propagation pathlength, propagation conditions, and beam parameters, such as the radius of the Gauss factor of the beam, parameter of the Bessel factor of the beam, topological charge, and correlation width of the source field of partially coherent radiation. It was found that, as a partially coherent vortex Bessel–Gaussian beam propagates through a turbulent atmosphere, there appear not two (as might be expected: one due to atmospheric turbulence and another due to the partial coherence of the source field), but only one ring dislocation of the coherence degree (due to the simultaneous effect of both these factors on the optical radiation). In addition, it is shown that the dislocation of the coherence degree that significantly affects the beam coherence level is formed only for beams, for which the coherence width of the source field is larger than the diameter of the first Fresnel zone. Full article
(This article belongs to the Special Issue Recent Advances in Diffractive Optics)
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16 pages, 6620 KiB  
Article
Long-Term Stability Test for Femtosecond Laser-Irradiated SnO2-Nanowire Gas Sensor for C7H8 Gas Sensing
by Sanghoon Ahn, Kang Woo Chun and Changkyoo Park
Photonics 2024, 11(6), 550; https://doi.org/10.3390/photonics11060550 - 11 Jun 2024
Cited by 5 | Viewed by 1689
Abstract
In this study, femtosecond (FS) laser irradiation with different laser energy densities of 138, 276, and 414 mJ/cm2 is applied to SnO2-nanowire (NW) gas sensors, and the effect of the FS laser irradiation on the gas sensor response toward toluene [...] Read more.
In this study, femtosecond (FS) laser irradiation with different laser energy densities of 138, 276, and 414 mJ/cm2 is applied to SnO2-nanowire (NW) gas sensors, and the effect of the FS laser irradiation on the gas sensor response toward toluene (C7H8) gas is investigated. The FS laser irradiation causes oxygen deficiency in the SnO2 NWs and forms SnO and SnOx. Moreover, an embossing surface with multiple nano-sized bumps is created on the SnO2 NW surface because of the FS laser irradiation. The FS laser-irradiated SnO2-NW gas sensor exhibits superior sensing performance compared with the pristine SnO2-NW gas sensor. Moreover, the FS laser energy density significantly affects gas-sensing performance, and the highest sensor response is achieved by the gas sensor irradiated at 138 mJ/cm2. The long-term stability test of the laser-irradiated SnO2-NW gas sensor is performed by comparing fresh and 6-month-old gas sensors in different gas concentrations and relative humidity levels. Comparable gas-sensing behaviors are examined between the fresh and 6-month-old gas sensor, and this verifies the robustness of the laser-irradiated SnO2-NW gas sensor. Full article
(This article belongs to the Special Issue Advances in Ultrafast Laser Science and Applications)
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18 pages, 24888 KiB  
Article
Miniaturized Multi-Platform Free-Space Laser-Communication Terminals for Beyond-5G Networks and Space Applications
by Alberto Carrasco-Casado, Koichi Shiratama, Dimitar Kolev, Fumie Ono, Hiroyuki Tsuji and Morio Toyoshima
Photonics 2024, 11(6), 545; https://doi.org/10.3390/photonics11060545 - 7 Jun 2024
Cited by 6 | Viewed by 4436
Abstract
Beyond-5G (B5G) technology plays a pivotal role in the next generation of communication infrastructure to support the future Society 5.0, a concept introduced in the 5th Basic Plan for Science and Technology by the Japanese Cabinet to define the long-term growth strategy for [...] Read more.
Beyond-5G (B5G) technology plays a pivotal role in the next generation of communication infrastructure to support the future Society 5.0, a concept introduced in the 5th Basic Plan for Science and Technology by the Japanese Cabinet to define the long-term growth strategy for reconciling economic development with the resolution of social issues through the promotion of science and technologies. Free-space laser communication is a key element in boosting the data transmission capabilities required for B5G applications. The NICT will complete in 2024 the first fully functional prototypes of a series of miniaturized laser-communication terminals for multiple platforms. These terminals are designed to adapt to a wide range of requirements to address scenarios where laser communications can offer a competitive, enhanced solution compared to existing technologies. This paper provides an overview of these terminals’ capabilities and the plans for their functional validation, as well as preliminary data from the first full-system tests. A number of innovations integrated into the terminals are introduced, such as the manufacture of the smallest miniaturized EDFA with integrated HPA and LNA and full space qualification to date, the first-ever integration of a beam-divergence control system in a practical communication terminal, the development of the most compact Tbit/s-class modem prototype documented in the literature, and the smallest gimbal design integrated in a lasercom terminal. Furthermore, this paper outlines the mid-term plans for demonstration in the most significant realistic scenarios, emphasizing the use of High-Altitude Platform Stations (HAPSs) and ultra-small satellites. Full article
(This article belongs to the Special Issue Recent Advances in Optical Wireless Communication Systems and Networks)
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22 pages, 1619 KiB  
Article
Optimisation of the Transmitter Layout in a VLP System Using an Aperture-Based Receiver
by José Miguel Menéndez and Heidi Steendam
Photonics 2024, 11(6), 517; https://doi.org/10.3390/photonics11060517 - 28 May 2024
Cited by 1 | Viewed by 1221
Abstract
In this paper, we consider a visible light positioning (VLP) system, where an array of photo diodes combined with apertures is used as a directional receiver and a set of inexpensive and energy-efficient light-emitting diodes (LEDs) is used as transmitters. The paper focuses [...] Read more.
In this paper, we consider a visible light positioning (VLP) system, where an array of photo diodes combined with apertures is used as a directional receiver and a set of inexpensive and energy-efficient light-emitting diodes (LEDs) is used as transmitters. The paper focuses on the optimisation of the layout of the transmitter, i.e., the number and placement of the LEDs, to meet the wanted position estimation accuracy levels. To this end, we evaluate the Cramer–Rao bound (CRB), which is a lower bound on the mean-squared error (MSE) of the position estimate, to analyse the influence of the LEDs’ placement. In contrast to other works, where only the location of the LEDs was considered and/or the optimisation was carried out through simulations, in this work, the optimisation is carried out analytically and considers all the parameters involved in the VLP system as well as the illumination. Based on our results, we formulate simple rules of thumb with which we can determine the spacing between LEDs and the minimum number of LEDs, as well as their position on the ceiling, while also taking into account the requirements for the illumination. Full article
(This article belongs to the Special Issue Advanced Technologies in Optical Wireless Communications)
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23 pages, 19086 KiB  
Article
Analysis of the Polarization Distribution and Spin Angular Momentum of the Interference Field Obtained by Co-Planar Beams with Linear and Circular Polarization
by Svetlana N. Khonina, Andrey V. Ustinov, Alexey P. Porfirev and Sergey V. Karpeev
Photonics 2024, 11(5), 478; https://doi.org/10.3390/photonics11050478 - 19 May 2024
Cited by 2 | Viewed by 1259
Abstract
Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation [...] Read more.
Interference of two and four light beams with linear or circular polarization is studied analytically and numerically based on the Richards–Wolf formalism. We consider such characteristics of the interference fields as the distribution of intensity, polarization, and spin angular momentum density. The generation of light fields with 1D and 2D periodic structure of both intensity and polarization is demonstrated. We can control the periodic structure both by changing the polarization state of the interfering beams and by changing the numerical aperture of focusing. We consider examples with a basic configuration, as well as those with a certain symmetry in the polarization state of the interfering beams. In some cases, increasing the numerical aperture of the focusing system significantly affects the generated distributions of both intensity and polarization. Experimental results, obtained using a polarization video camera, are in good agreement with the simulation results. The considered light fields can be used in laser processing of thin films of photosensitive (as well as polarization-sensitive) materials in order to create arrays of various ordered nano- and microstructures. Full article
(This article belongs to the Special Issue Structured Light Beams: Science and Applications)
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15 pages, 5146 KiB  
Article
A Fast Time Synchronization Method for Large Scale LEO Satellite Networks Based on A Bionic Algorithm
by Yue Xu, Tao Dong, Jie Yin, Ziyong Zhang, Zhihui Liu, Hao Jiang and Jing Wu
Photonics 2024, 11(5), 475; https://doi.org/10.3390/photonics11050475 - 19 May 2024
Cited by 1 | Viewed by 2126
Abstract
A fast time synchronization method for large-scale LEO satellite networks based on a bionic algorithm is proposed. Because the inter-satellite links are continuously established and interrupted due to the relative motion of the satellites, the topology of the LEO satellite networks is time [...] Read more.
A fast time synchronization method for large-scale LEO satellite networks based on a bionic algorithm is proposed. Because the inter-satellite links are continuously established and interrupted due to the relative motion of the satellites, the topology of the LEO satellite networks is time varying. Firstly, according to the ephemeris information in navigation messages, a connection table which records the connections between satellites is generated. Then, based on the connection table, the current satellite network topology is calculated and generated. Furthermore, a bionic algorithm is used to select some satellites as time source nodes and calculate the hierarchy of the clock transmission tree. By taking the minimum level of the time transmission tree as the optimization objective, the time source nodes and the clock stratums of the whole satellite networks are obtained. Finally, the onboard computational center broadcasts the time layer table to all the satellites in the LEO satellite networks and the time synchronization links can be established or recovered fast. Full article
(This article belongs to the Special Issue Novel Advances in Optical Communications)
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12 pages, 15402 KiB  
Article
Compact Low Loss Ribbed Asymmetric Multimode Interference Power Splitter
by Yanfeng Liang, Huanlin Lv, Baichao Liu, Haoyu Wang, Fangxu Liu, Shuo Liu, Yang Cong, Xuanchen Li and Qingxiao Guo
Photonics 2024, 11(5), 472; https://doi.org/10.3390/photonics11050472 - 17 May 2024
Cited by 2 | Viewed by 2011
Abstract
Optical power splitters (OPSs) are utilized extensively in integrated photonic circuits, drawing significant interest in research on power splitters with adjustable splitting ratios. This paper introduces a compact, low-loss 1 × 2 asymmetric multimode interferometric (MMI) optical power splitter on a silicon-on-insulator (SOI) [...] Read more.
Optical power splitters (OPSs) are utilized extensively in integrated photonic circuits, drawing significant interest in research on power splitters with adjustable splitting ratios. This paper introduces a compact, low-loss 1 × 2 asymmetric multimode interferometric (MMI) optical power splitter on a silicon-on-insulator (SOI) platform. The device is simulated using the finite difference method (FDM) and eigenmode expansion solver (EME). It is possible to attain various output power splitting ratios by making the geometry of the MMI central section asymmetric relative to the propagation axis. Six distinct optical power splitters are designed with unconventional splitting ratios in this paper, which substantiates that the device can achieve any power splitter ratios (PSRs) in the range of 95:5 to 50:50. The dimensions of the multimode section were established at 2.9 × (9.5–10.9) μm. Simulation results show a range of unique advantages of the device, including a low extra loss of less than 0.4 dB, good fabrication tolerance, and power splitting ratio fluctuation below 3% across the 1500 nm to 1600 nm wavelength span. Full article
(This article belongs to the Special Issue Optical Fiber Communication Systems and Networks)
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11 pages, 4949 KiB  
Article
The Generation of Circularly Polarized Isolated Attosecond Pulses with Tunable Helicity from CO Molecules in Polarization Gating Laser Fields
by Shiju Chen, Hua Yuan, Feng Wang, Jiahang Song, Yue Zhao, Chunhui Yang, Tianxin Ou, Ru Zhang, Qiang Chang and Yuping Sun
Photonics 2024, 11(5), 464; https://doi.org/10.3390/photonics11050464 - 15 May 2024
Viewed by 1680
Abstract
We theoretically demonstrate a scheme to generate circularly polarized (CP) isolated attosecond pulses (IAPs) with tunable helicity using a polarization gating laser field interacting with the CO molecule. The results show that a broadband CP supercontinuum is produced from the oriented CO molecule, [...] Read more.
We theoretically demonstrate a scheme to generate circularly polarized (CP) isolated attosecond pulses (IAPs) with tunable helicity using a polarization gating laser field interacting with the CO molecule. The results show that a broadband CP supercontinuum is produced from the oriented CO molecule, which supports the generation of an IAP with an ellipticity of 0.98 and a duration of 90 as. Furthermore, the helicity of the generated harmonics and IAP can be effectively controlled by modulating the laser field and the orientation angle of the CO molecule. Our method will advance research on chiral-specific dynamics and magnetic circular dichroism on the attosecond timescale. Full article
(This article belongs to the Topic Recent Advances in Nonlinear Optics and Nonlinear Optical Materials)
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16 pages, 3641 KiB  
Review
Features of Adaptive Phase Correction of Optical Wave Distortions under Conditions of Intensity Fluctuations
by Vladimir Lukin
Photonics 2024, 11(5), 460; https://doi.org/10.3390/photonics11050460 - 14 May 2024
Cited by 2 | Viewed by 1749
Abstract
An analysis of the features of measurements and correction of phase distortions in optical waves propagating in the atmosphere at various levels of turbulence was performed. It is shown that with increasing intensity fluctuations, the limiting capabilities of phase correction decrease, and the [...] Read more.
An analysis of the features of measurements and correction of phase distortions in optical waves propagating in the atmosphere at various levels of turbulence was performed. It is shown that with increasing intensity fluctuations, the limiting capabilities of phase correction decrease, and the phase of an optical wave that has passed through a turbulence layer consists of two components: potential and vortex. It was found that even in the region of weak fluctuations there is an overlap of spectral filtering functions for intensity and phase fluctuations. Areas of turbulence inhomogeneities have been identified that will have mutual influence and negatively affect the operation of the phase meter. It is noted that correlation functions, both phase and intensity, are less susceptible to this compared to structural functions. The results of experimental studies on the reconstruction of the wavefront of laser radiation distorted by atmospheric turbulence using a Shack–Hartmann wavefront sensor during vignetting and central screening of the entrance pupil in the optical system are presented. Studies have been carried out on the propagation of laser radiation along a horizontal atmospheric path for various levels of turbulence. The results are analyzed in terms of Zernike polynomials. Full article
(This article belongs to the Special Issue Advances in Structured Light Generation and Manipulation)
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14 pages, 5228 KiB  
Article
Analytical Model of Point Spread Function under Defocused Degradation in Diffraction-Limited Systems: Confluent Hypergeometric Function
by Feijun Song, Qiao Chen, Xiongxin Tang and Fanjiang Xu
Photonics 2024, 11(5), 455; https://doi.org/10.3390/photonics11050455 - 13 May 2024
Cited by 2 | Viewed by 2285
Abstract
In recent years, optical systems near the diffraction limit have been widely used in high-end applications. Evidently, an analytical solution of the point spread function (PSF) will help to enhance both understanding and dealing with the imaging process. This paper analyzes the Fresnel [...] Read more.
In recent years, optical systems near the diffraction limit have been widely used in high-end applications. Evidently, an analytical solution of the point spread function (PSF) will help to enhance both understanding and dealing with the imaging process. This paper analyzes the Fresnel diffraction of diffraction-limited optical systems in defocused conditions. For this work, an analytical solution of the defocused PSF was obtained using the series expansion of the confluent hypergeometric functions. The analytical expression of the defocused optical transfer function is also presented herein for comparison with the PSF. Additionally, some characteristic parameters for the PSF are provided, such as the equivalent bandwidth and the Strehl ratio. Comparing the PSF obtained using the fast Fourier transform algorithm of an optical system with known, detailed parameters to the analytical solution derived in this paper using only the typical parameters, the root mean square errors of the two methods were found to be less than 3% in the weak and medium defocus range. The attractive advantages of the universal model, which is independent of design details, objective types, and applications, are discussed. Full article
(This article belongs to the Special Issue Emerging Topics in High-Power Laser and Light–Matter Interactions)
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9 pages, 874 KiB  
Article
Penrose Scattering in Quantum Vacuum
by José Tito Mendonça
Photonics 2024, 11(5), 448; https://doi.org/10.3390/photonics11050448 - 10 May 2024
Cited by 1 | Viewed by 5497
Abstract
This paper considers the scattering of a probe laser pulse by an intense light spring in a QED vacuum. This new scattering configuration can be seen as the vacuum equivalent to the process originally associated with the scattering of light by a rotating [...] Read more.
This paper considers the scattering of a probe laser pulse by an intense light spring in a QED vacuum. This new scattering configuration can be seen as the vacuum equivalent to the process originally associated with the scattering of light by a rotating black hole, which is usually called Penrose superradiance. Here, the rotating object is an intense laser beam containing two different components of orbital angular momentum. Due to these two components having slightly different frequencies, the energy profile of the intense laser beam rotates with an angular velocity that depends on the frequency difference. The nonlinear properties of a quantum vacuum are described by a first-order Euler–Heisenberg Lagrangian. It is shown that in such a configuration, nonlinear photon–photon coupling leads to scattered radiation with frequency shift and angular dispersion. These two distinct properties, of frequency and propagation direction, could eventually be favorable for possible experimental observations. In principle, this new scattering configuration can also be reproduced in a nonlinear optical medium. Full article
(This article belongs to the Special Issue Extreme Lasers)
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77 pages, 9183 KiB  
Review
Synergy between AI and Optical Metasurfaces: A Critical Overview of Recent Advances
by Zoran Jakšić
Photonics 2024, 11(5), 442; https://doi.org/10.3390/photonics11050442 - 9 May 2024
Cited by 5 | Viewed by 9621
Abstract
The interplay between two paradigms, artificial intelligence (AI) and optical metasurfaces, nowadays appears obvious and unavoidable. AI is permeating literally all facets of human activity, from science and arts to everyday life. On the other hand, optical metasurfaces offer diverse and sophisticated multifunctionalities, [...] Read more.
The interplay between two paradigms, artificial intelligence (AI) and optical metasurfaces, nowadays appears obvious and unavoidable. AI is permeating literally all facets of human activity, from science and arts to everyday life. On the other hand, optical metasurfaces offer diverse and sophisticated multifunctionalities, many of which appeared impossible only a short time ago. The use of AI for optimization is a general approach that has become ubiquitous. However, here we are witnessing a two-way process—AI is improving metasurfaces but some metasurfaces are also improving AI. AI helps design, analyze and utilize metasurfaces, while metasurfaces ensure the creation of all-optical AI chips. This ensures positive feedback where each of the two enhances the other one: this may well be a revolution in the making. A vast number of publications already cover either the first or the second direction; only a modest number includes both. This is an attempt to make a reader-friendly critical overview of this emerging synergy. It first succinctly reviews the research trends, stressing the most recent findings. Then, it considers possible future developments and challenges. The author hopes that this broad interdisciplinary overview will be useful both to dedicated experts and a general scholarly audience. Full article
(This article belongs to the Special Issue Recent Advances in Diffractive Optics)
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26 pages, 9970 KiB  
Article
An Empirical Approach to Rerouting Visible Light Pathways Using an Adjustable-Angle Mirror to Sustain Communication between Vehicles on Curvy Roads
by Ahmet Deniz, Burak Aydın and Heba Yuksel
Photonics 2024, 11(5), 426; https://doi.org/10.3390/photonics11050426 - 3 May 2024
Cited by 2 | Viewed by 1887
Abstract
In this paper, a novel method is demonstrated to sustain vehicle-to-vehicle (V2V) communication on curvy roads via the arrangement of the lateral position of a self-angle-adjustable mirror–reflective road sign (SAAMRS) and light-direction-sensing wide-angle complementary photodiodes (CPDs). Visible light communication (VLC) between vehicles attracts [...] Read more.
In this paper, a novel method is demonstrated to sustain vehicle-to-vehicle (V2V) communication on curvy roads via the arrangement of the lateral position of a self-angle-adjustable mirror–reflective road sign (SAAMRS) and light-direction-sensing wide-angle complementary photodiodes (CPDs). Visible light communication (VLC) between vehicles attracts attention as a complementary technology to radio-frequency-based (RF-based) communication technologies due to its wide, license-free spectrum and immunity to interferences. However, V2V VLC may be interrupted on curvy roads due to the limited field of view (FOV) of the receiver or the line of sight (LOS) being interrupted. To solve this problem, an experiment was developed using an SAAMRS along with wide-angle light-direction-sensing CPDs that used a precise peak detection (PPD) method to sustain communication between vehicles in dynamic environments by rerouting the incident light with the highest signal intensity level to the receiver vehicle on curvy roads. We also used real images of curvy roads simulated as polynomials to calculate the necessary rotation angles for the SAAMRS and regions where communication exist. Our experimental results overlapped almost completely with our simulations, with small errors of approximately 4.8% and 4.4% for the SAAMRS angle and communication region, respectively. Full article
(This article belongs to the Special Issue Visible Light Communications)
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14 pages, 12042 KiB  
Article
Tightly Trapped Atom Interferometer inside a Hollow-Core Fiber
by Yitong Song, Wei Li, Xiaobin Xu, Rui Han, Chengchun Gao, Cheng Dai and Ningfang Song
Photonics 2024, 11(5), 428; https://doi.org/10.3390/photonics11050428 - 3 May 2024
Cited by 5 | Viewed by 2042
Abstract
We demonstrate a fiber-guided atom interferometer in a far-off-resonant trap (FORT) of 100 μK. The differential light shift (DLS) introduced by the FORT leads to the inhomogeneous dephasing of the tightly trapped atoms inside a hollow-core fiber. The DLS-induced dephasing is greatly suppressed [...] Read more.
We demonstrate a fiber-guided atom interferometer in a far-off-resonant trap (FORT) of 100 μK. The differential light shift (DLS) introduced by the FORT leads to the inhomogeneous dephasing of the tightly trapped atoms inside a hollow-core fiber. The DLS-induced dephasing is greatly suppressed in π/2-π-π/2 Doppler-insensitive interferometry. The spin coherence time is extended to 13.4 ms by optimizing the coupling of the trapping laser beam into a quasi-single-mode hollow-core anti-resonant fiber. The Doppler-sensitive interferometry shows a much shorter coherence time, indicating that the main limits to our fiber-guided atom interferometer are the wide axial velocity distribution and the irregular modes of the Raman laser beams inside the fiber. This work paves the way for portable and miniaturized quantum devices, which have advantages for inertial sensing at arbitrary orientations and in dynamic environments. Full article
(This article belongs to the Special Issue The Integration of Quantum Communication and Quantum Sensors)
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11 pages, 2759 KiB  
Article
Photoluminescence Enhancement and Carrier Dynamics of Charged Biexciton in Monolayer WS2 Coupled with Plasmonic Nanocavity
by Huiqiang Geng, Qirui Liu, Yuxiang Tang and Ke Wei
Photonics 2024, 11(4), 358; https://doi.org/10.3390/photonics11040358 - 12 Apr 2024
Cited by 2 | Viewed by 1693
Abstract
Monolayer two-dimensional transition metal dichalcogenide (TMD)-based materials have become one of the ideal platforms for the study of multibody interactions due to their rich excitonic complexes. The coupling between optical nanocavity and material has become an important means for manipulating the optical properties [...] Read more.
Monolayer two-dimensional transition metal dichalcogenide (TMD)-based materials have become one of the ideal platforms for the study of multibody interactions due to their rich excitonic complexes. The coupling between optical nanocavity and material has become an important means for manipulating the optical properties of materials, but there are few studies on the coupling of nanocavities and the multi-body effect in materials. In this study, we investigate the optical properties of silver nanodisk (Ag ND) arrays covering a monolayer WS2. In the experimental sample, we observed a ~114.3-fold photoluminescence enhancement of charged biexciton in the heterostructure region, as compared to the monolayer WS2 region, a value which is much higher than those for exciton (~2.2-fold) and trion (~16.4-fold), a finding which is attributed to the Fano resonant coupling between monolayer WS2 and the Ag ND. By means of time-resolved spectroscopy, we studied the carrier dynamics in the hybrid system. Our findings reveal that resonant coupling promotes the formation and radiation recombination processes of the charged biexciton, significantly reducing the radiative recombination lifetime by ~15-fold, which is much higher than the measurement in exciton (~2-fold). Our results provide an opportunity to understand the multibody physics of coupling with nanocavities, which could facilitate the application of multi-body excitons in the fields of light-emitting devices and lasers, etc. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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11 pages, 755 KiB  
Article
Moving Bragg Solitons in a Dual-Core System Composed of a Linear Bragg Grating with Dispersive Reflectivity and a Uniform Nonlinear Core
by Tanvir Ahmed and Javid Atai
Photonics 2024, 11(4), 324; https://doi.org/10.3390/photonics11040324 - 30 Mar 2024
Viewed by 1153
Abstract
The existence and stability of moving Bragg grating solitons are systematically investigated in a dual-core system, where one core is uniform and has Kerr nonlinearity, and the other is linear with Bragg grating and dispersive reflectivity. It is found that moving soliton solutions [...] Read more.
The existence and stability of moving Bragg grating solitons are systematically investigated in a dual-core system, where one core is uniform and has Kerr nonlinearity, and the other is linear with Bragg grating and dispersive reflectivity. It is found that moving soliton solutions exist throughout the upper and lower bandgaps, whereas no soliton solutions exist in the central bandgap. Similar to the quiescent solitons in the system, it is found that when dispersive reflectivity is nonzero, for certain values of parameters, sidelobes appear in the solitons’ profiles. The stability of the moving solitons is characterized using systematic numerical stability analysis. Additionally, the impact and interplay of dispersive reflectivity, soliton velocity, and group velocity on the stability border are analyzed. Full article
(This article belongs to the Special Issue Nonlinear Propagation in Optical Fiber Application)
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16 pages, 1234 KiB  
Article
A Best-Path Approach to the Design of a Hybrid Space–Ground Quantum Network with Dynamic Constraints
by David L. Bakker, Yannick Jong, Bob P. F. Dirks and Gustavo C. Amaral
Photonics 2024, 11(3), 268; https://doi.org/10.3390/photonics11030268 - 18 Mar 2024
Cited by 3 | Viewed by 2336
Abstract
The design and operation of quantum networks are both decisive in the current push towards a global quantum internet. Although space-enabled quantum connectivity has already been identified as a beneficial candidate for long-range quantum channels for over two decades, the architecture of a [...] Read more.
The design and operation of quantum networks are both decisive in the current push towards a global quantum internet. Although space-enabled quantum connectivity has already been identified as a beneficial candidate for long-range quantum channels for over two decades, the architecture of a hybrid space–ground network is still a work in progress. Here, we propose an analysis of such a network based on a best-path approach, where either fiber- or satellite-based elementary links can be concatenated to form a repeater chain. The network consisting of quantum information processing nodes, equipped with both ground and space connections, is mapped into a graph structure, where edge weights represent the achievable secret key rates, chosen as the figure of merit for the network analysis. A weight minimization algorithm allows for identifying the best path dynamically, i.e., as the weather conditions, stray light radiance, and satellite orbital position change. From the results, we conclude that satellite links will play a significant role in the future large-scale quantum internet, in particular when node distances exceed 500 km, and both a constellation of satellites—spanning 20 or more satellites—and significant advances in filtering technology are required to achieve continuous coverage. Full article
(This article belongs to the Special Issue Optical Satellite Communications for Quantum Networking)
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15 pages, 8725 KiB  
Article
Multi-Layered Metamaterial Absorber: Electromagnetic and Thermal Characterization
by Bui Xuan Khuyen, Ngo Nhu Viet, Pham Thanh Son, Bui Huu Nguyen, Nguyen Hai Anh, Do Thuy Chi, Nguyen Phon Hai, Bui Son Tung, Vu Dinh Lam, Haiyu Zheng, Liangyao Chen and Youngpak Lee
Photonics 2024, 11(3), 219; https://doi.org/10.3390/photonics11030219 - 28 Feb 2024
Cited by 6 | Viewed by 3687
Abstract
Metamaterials, recognized as advanced artificial materials endowed with distinctive properties, have found diverse applications in everyday life, military endeavors, and scientific research. Starting from monolayer metamaterials, multilayer ones are increasingly researched, especially in the field of electromagnetic wave absorption. In this article, we [...] Read more.
Metamaterials, recognized as advanced artificial materials endowed with distinctive properties, have found diverse applications in everyday life, military endeavors, and scientific research. Starting from monolayer metamaterials, multilayer ones are increasingly researched, especially in the field of electromagnetic wave absorption. In this article, we propose a multilayer metamaterial-absorber (MA) structure comprising two resonant layers crafted with copper and FR-4 dielectric. The presented multilayer MA structure exhibited an absorption greater than 90% in a frequency range from 4.84 to 5.02 GHz, with two maximum absorption peaks at 4.89 and 4.97 GHz. The bandwidth of the multilayer MA surpassed that of the individual single-layer MAs, with extension fractions reaching 360% and 257%, respectively. Through the simulation and calculation, the field distribution and equivalent circuit model elucidated that both individual magnetic resonances and their interplay contribute significantly to the absorption behavior of the multilayer MA. The absorption of the proposed multilayer MA structure was also investigated for the oblique incidence in the transverse electric (TE) and transverse magnetic (TM) modes. In the TE mode, the absorption intensity of two maximum peaks was maintained at over 93% up to an incident angle of 40 degrees and dropped to below 80% at an incident angle of 60 degrees. In the TM mode, the absorption was more stable and not significantly affected by the incident angle, ranging from 0 to 60 degrees. An absorption greater than 97% was observed when the incident angle increased from 0 to 60 degrees in the TM mode. Additionally, the approach in our work was further demonstrated by adding more resonant layers, making 3- and 4-layer structures. The results indicated that the absorption bandwidths of the 3- and 4-layer structures increased by 16% and 33%, respectively, compared to the bilayer structure. Furthermore, we analyzed the thermal distribution within the MA to understand the dissipation of absorbed electromagnetic energy. This research offers valuable insight into the augmented MA through a multilayer structure, presenting the implications for microwave applications like electromagnetic shielding, as well as in the design of MAs for terahertz devices and technologies, including emission and thermal imaging. These findings contribute to the advancement of knowledge in enhancing the absorption capabilities across various frequency ranges, expanding the potential applications of metamaterials. Full article
(This article belongs to the Special Issue Advanced Photonics Metamaterials and Metasurfaces: Science and Applications)
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15 pages, 4229 KiB  
Review
Recent Advances, Applications, and Perspectives in Erbium-Doped Fiber Combs
by Pengpeng Yan, Weiming Xu, Heng Hu, Zhenqiang Zhang, Zhaoyang Li and Rong Shu
Photonics 2024, 11(3), 192; https://doi.org/10.3390/photonics11030192 - 21 Feb 2024
Cited by 5 | Viewed by 3089
Abstract
Optical frequency combs have emerged as a new generation of metrological tools, driving advancements in various fields such as free-space two-way time–frequency transfer, low-noise microwave source generation, and gas molecule detection. Among them, fiber combs based on erbium-doped fiber mode-locked lasers have garnered [...] Read more.
Optical frequency combs have emerged as a new generation of metrological tools, driving advancements in various fields such as free-space two-way time–frequency transfer, low-noise microwave source generation, and gas molecule detection. Among them, fiber combs based on erbium-doped fiber mode-locked lasers have garnered significant attention due to their numerous advantages, including low noise, high system integration, and cost-effectiveness. In this review, we discuss recent developments in erbium-doped fiber combs and analyze the advantages and disadvantages of constructing fiber combs utilizing different erbium-doped mode-locked fiber lasers. First, we provide a brief introduction to the basic principles of optical frequency combs. Then, we explore erbium-doped fiber combs implemented utilizing various mode-locking techniques, such as nonlinear polarization rotation (NPR), real saturable absorber (SA), and nonlinear amplifying loop mirror (NALM). Finally, we present an outlook on the future perspectives of erbium-doped fiber combs. Full article
(This article belongs to the Special Issue Advances in Sensoring and Measurement with Optical Frequency Comb)
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16 pages, 4382 KiB  
Article
Multispectral Narrowband Frustrated Total Internal Reflection Filter with Inclusions of Plasmonic Nanoparticles
by Nikolai I. Petrov
Photonics 2024, 11(2), 180; https://doi.org/10.3390/photonics11020180 - 16 Feb 2024
Cited by 1 | Viewed by 1648
Abstract
A spatial-frequency thin-film filter with inclusions of nanoparticles operating in the visible range of the spectrum is investigated. The effect of nanoparticles embedded in the central and lateral layers of the frustrated total internal reflection filter on the spectral characteristics, considering the frequency [...] Read more.
A spatial-frequency thin-film filter with inclusions of nanoparticles operating in the visible range of the spectrum is investigated. The effect of nanoparticles embedded in the central and lateral layers of the frustrated total internal reflection filter on the spectral characteristics, considering the frequency dispersion, is investigated. It is shown that plasmonic effects cause the splitting of the filter bandwidth into a set of narrow-band spectral lines and the angular splitting of the incident beam into a set of output beams. It is demonstrated that due to the difference in the resonance conditions for s- and p-polarization waves, the spectral lines of transparency do not coincide, which indicates the possibility of using the filter as a polarizer. Full article
(This article belongs to the Special Issue Recent Advances in Diffractive Optics)
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9 pages, 1788 KiB  
Article
Efficient Third Harmonic Generation from Magnetic Resonance in Low-Index Dielectric Nanopillars
by Rui Xie, Xiaobo He, Wenqiang Wang, Liren Zheng and Junjun Shi
Photonics 2024, 11(2), 159; https://doi.org/10.3390/photonics11020159 - 7 Feb 2024
Cited by 3 | Viewed by 2019
Abstract
Boosting the harmonic generation of light in nanostructures through efficiently enhancing the light–matter interaction has received enormous attention and applications. Low-index dielectric nanoparticles, as one of the crucial members of nanophotonics, have not been successful in nonlinear enhancement due to weak Mie resonance [...] Read more.
Boosting the harmonic generation of light in nanostructures through efficiently enhancing the light–matter interaction has received enormous attention and applications. Low-index dielectric nanoparticles, as one of the crucial members of nanophotonics, have not been successful in nonlinear enhancement due to weak Mie resonance and poor light confinement. Here, we designed efficient third harmonic generation (THG) in low-index dielectric nanopillars sandwiched by double layers of metal dressing (Au/polymer/Au), where the polymer offers essential nonlinear susceptibility. The resonance of the low-index nanopillars significantly enhanced the scattering and had a strong magnetic response that could boost the THG effect. We predict that the THG efficiency reaches up to 3 × 10−6 (six orders of enhancement) at a third harmonic wavelength of 300 nm. The efficient THG in low-index dielectric nanopillars may open the possibility for the development of a new type of efficient nonlinear coherent source. Full article
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11 pages, 495 KiB  
Article
A Promising Route to Compact and Economic Sub-15 fs, PW-Level Ti:Sapphire Lasers
by Fenxiang Wu, Jiabing Hu, Zongxin Zhang, Yang Zhao, Peile Bai, Haidong Chen, Xun Chen, Yi Xu, Yuxin Leng and Ruxin Li
Photonics 2024, 11(2), 121; https://doi.org/10.3390/photonics11020121 - 28 Jan 2024
Cited by 1 | Viewed by 2044
Abstract
In quest of achieving compact and economic PW-level Ti:Sapphire (Ti:sa) lasers with a sub-15 fs pulse duration, a modified hybrid amplification scheme, which combines the optical parametric chirped pulse amplifier (OPCPA) and the chirped pulse amplifier (CPA), is presented and numerically investigated in [...] Read more.
In quest of achieving compact and economic PW-level Ti:Sapphire (Ti:sa) lasers with a sub-15 fs pulse duration, a modified hybrid amplification scheme, which combines the optical parametric chirped pulse amplifier (OPCPA) and the chirped pulse amplifier (CPA), is presented and numerically investigated in this paper. The key characteristic of this scheme is that the conventional Ti:sa regenerative amplifier and preamplifier are replaced by a dual-crystal OPCPA front-end, which is spectrally matched with the upstream seed source and the downstream Ti:sa amplifiers and, therefore, can realize a broader spectrum. Moreover, some useful laser techniques are also applied to suppress the spectral gain narrowing and redshift in the Ti:sa CPA chain and to control the residual dispersion in the laser system. This way, fewer amplification stages and pump lasers are required to reach PW-level peak power compared with traditional all-CPA Ti:sa lasers. Numerical results indicate that pulse energy and spectral bandwidth can reach up to ∼22 J and ∼125 nm at full width at half maximum (FWHM), respectively, only by employing three-stage amplifiers. After compression, PW-level lasers with a ∼13.3 fs pulse duration are expected. This work can offer a promising route for the development of compact and economic PW-level Ti:sa lasers. Full article
(This article belongs to the Special Issue Ultrashort Ultra-Intense (Petawatt) Laser)
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11 pages, 2290 KiB  
Article
Optimization of the Spot Spacings for Reducing Roughness in Laser-Induced Optical Breakdown Processes for Corneal Laser Vision Correction
by Helen Amann and Samuel Arba Mosquera
Photonics 2024, 11(2), 114; https://doi.org/10.3390/photonics11020114 - 26 Jan 2024
Cited by 3 | Viewed by 2096
Abstract
The aim of this work is to implement an algorithm that simulates a simplified cutting surface based on laser-induced optical breakdown (LIOB). The algorithm includes the definition of a possible positioning of the laser pulses and calculation of the roughness for different parameter [...] Read more.
The aim of this work is to implement an algorithm that simulates a simplified cutting surface based on laser-induced optical breakdown (LIOB). The algorithm includes the definition of a possible positioning of the laser pulses and calculation of the roughness for different parameter settings (including LIOB threshold, pulse energies, and spot spacings) as the difference between simulated and ideal target cut (local differences within the cut, i.e., the waviness of the simulated cut vs. the homogeneity of the ideal target cut). Furthermore, optimizations of specific variables, such as spot distance (along the pathway), track distance (between lines/tracks), and pulse energy, are performed. The simulations suggest that lower pulse energies (well above the LIOB threshold) combined with asymmetric spacings (spot-to-track distance ratio >> 1) may be effective to lower the roughness of laser cuts generated by LIOB processes. The importance of lowering pulse energies (well above the threshold) emphasizes the need for the LIOB threshold to remain low (as low as possible). Reducing roughness by decreasing spacings (thus, increasing dose for same pulse energies) may have negative implications in visual recovery (risk for overdose). In all cases, the roughness is multiple times larger (rougher) than equivalent simulations for ablative procedures. Full article
(This article belongs to the Special Issue Visual Optics)
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21 pages, 56300 KiB  
Review
Optical Imaging Using Coded Aperture Correlation Holography (COACH) with PSF of Spatial-Structured Longitudinal Light Beams—A Study Review
by Joseph Rosen and Vijayakumar Anand
Photonics 2024, 11(2), 115; https://doi.org/10.3390/photonics11020115 - 26 Jan 2024
Cited by 5 | Viewed by 2369
Abstract
Spatial-structured longitudinal light beams are optical fields sculpted in three-dimensional (3D) space by diffractive optical elements. These beams have been recently suggested for use in improving several imaging capabilities, such as 3D imaging, enhancing image resolution, engineering the depth of field, and sectioning [...] Read more.
Spatial-structured longitudinal light beams are optical fields sculpted in three-dimensional (3D) space by diffractive optical elements. These beams have been recently suggested for use in improving several imaging capabilities, such as 3D imaging, enhancing image resolution, engineering the depth of field, and sectioning 3D scenes. All these imaging tasks are performed using coded aperture correlation holography systems. Each system designed for a specific application is characterized by a point spread function of a different spatial-structured longitudinal light beam. This article reviews the topic of applying certain structured light beams for optical imaging. Full article
(This article belongs to the Special Issue Structured Light Beams: Science and Applications)
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12 pages, 6906 KiB  
Article
A 2 µm Gallium Antimonide Semiconductor Laser Based on Slanted, Wedge-Shaped Microlens Fiber Coupling
by Zhaohong Liu, Jiayue Wang, Ning Li, Zhongwei Yang, Shaowen Li, Sensen Li, Wei Wang, Heshig Bayan, Weining Cheng, Yu Zhang, Zhuokun Wu, Hongyu Sun, Yuanqing Xia, Yulei Wang and Zhiwei Lu
Photonics 2024, 11(2), 108; https://doi.org/10.3390/photonics11020108 - 25 Jan 2024
Cited by 3 | Viewed by 1756
Abstract
Semiconductor lasers with a wavelength of 2 µm, composed of antimonide materials, find important applications in trace gas detection, laser medicine, and free-space optical communication, among others. In this paper, a more suitable microlens shape for 2 µm gallium antimonide semiconductor lasers is [...] Read more.
Semiconductor lasers with a wavelength of 2 µm, composed of antimonide materials, find important applications in trace gas detection, laser medicine, and free-space optical communication, among others. In this paper, a more suitable microlens shape for 2 µm gallium antimonide semiconductor lasers is designed. Based on the fiber coupling efficiency model, the parameters of the designed slanting wedge-shaped microlens fiber are optimized to improve laser beam quality. The large tangent angle on both sides of the slanted, wedge-shaped microlens fiber is calculated using Snell’s law, and the fiber core diameter and small wedge angle are determined through space fiber coupling experiments. After packaging the fiber coupling module with the chip, the laser output beam exhibits good overall symmetry in the spot with a uniform intensity distribution. The maximum output power is approximately 210 mW, demonstrating good power stability. Full article
(This article belongs to the Special Issue Emerging Topics in High-Power Laser and Light–Matter Interactions)
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11 pages, 2187 KiB  
Article
Analysis of the Influence of Fabrication Errors on the Far-Field Performance of Si and Si3N4 Antennas
by Yifan Xin, Wenyuan Liao, Lei Yu, Pengfei Ma, Zheng Wang, Yibo Yang, Licheng Chen, Pengfei Wang, Yejin Zhang and Jiaoqing Pan
Photonics 2024, 11(1), 81; https://doi.org/10.3390/photonics11010081 - 16 Jan 2024
Cited by 1 | Viewed by 1640
Abstract
Antennas are important components in optical phased arrays. However, their far-field performance deteriorates when random phase noise is introduced because of fabricating errors. For the first time, we use a finite-difference time-domain solution to quantitatively analyze the far-field characteristics of Si and Si [...] Read more.
Antennas are important components in optical phased arrays. However, their far-field performance deteriorates when random phase noise is introduced because of fabricating errors. For the first time, we use a finite-difference time-domain solution to quantitatively analyze the far-field characteristics of Si and Si3N4 antennas considering process errors. Under rough surface conditions based on a fishbone structure, we find that the quality of the main lobe of the Si antenna deteriorates badly, with −0.87 dB and −0.51 dB decreases in the sidelobe level and 5.78% and 3.74% deteriorations in the main peak power in the φ (phase-controlled) and θ (wavelength-controlled) directions, respectively. However, the Si3N4 antenna is only slightly impacted, with mere 0.39% and 0.71% deteriorations in the main peak power in the φ and θ directions, respectively, which is statistically about 1/15 of the Si antenna in the φ direction and 1/5 in the θ direction. The decreases in the sidelobe level are also slight, at about −0.08 dB and −0.01 dB, respectively. Furthermore, the advantages of the Si3N4 antenna become more remarkable with the introduction of random errors into the waveguide width and thickness. This work is of great significance for the design and optimization of OPA chips. Full article
(This article belongs to the Special Issue Sciences and Applications of Nano-Photonics)
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8 pages, 2003 KiB  
Communication
The Design and Characterization of an Ultra-Compact Asymmetrical Multimode Interference Splitter on Lithium Niobate Thin Film
by Dechen Li, Jinye Li, Run Li and Jianguo Liu
Photonics 2024, 11(1), 60; https://doi.org/10.3390/photonics11010060 - 5 Jan 2024
Cited by 7 | Viewed by 3027
Abstract
We propose and demonstrate a high-performance asymmetrical multimode interference splitter on X-cut lithium niobate on insulator (LNOI) with an ultra-compact size of 5.8 μm × (26.4–35.6) μm. A rectangle with a small region is removed from the upper left corner of the multimode [...] Read more.
We propose and demonstrate a high-performance asymmetrical multimode interference splitter on X-cut lithium niobate on insulator (LNOI) with an ultra-compact size of 5.8 μm × (26.4–35.6) μm. A rectangle with a small region is removed from the upper left corner of the multimode interference (MMI) coupler to achieve a variable splitting ratio. Here, we design and characterize MMIs in six different distribution ratios ranging from 50:50 to 95:5 on a 600 nm thick LNOI. Based on the cascade structure, the linear fitting method accurately shows the device loss (~0.1–0.9 dB). Our fabricated devices demonstrate robustness across a 30 nm optical bandwidth (1535–1565 nm). In addition, we numerically simulate the Z-cut LNOI, showing that the structure corresponding to the TM mode can also achieve a good variable splitting ratio. Full article
(This article belongs to the Special Issue Photonics Integration on Silicon-on-Insulator and Thin-Film Lithium Niobate Platforms)
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17 pages, 928 KiB  
Article
Cooperative Terrestrial–Underwater FSO System: Design and Performance Analysis
by Carmen Álvarez-Roa, María Álvarez-Roa, Thiago R. Raddo, Antonio Jurado-Navas and Miguel Castillo-Vázquez
Photonics 2024, 11(1), 58; https://doi.org/10.3390/photonics11010058 - 5 Jan 2024
Cited by 4 | Viewed by 2740
Abstract
In this paper, we propose, design, and evaluate a new hybrid terrestrial–underwater optical communication link for providing high-speed connectivity between land and underwater systems. A device based on an amplify-and-forward strategy is considered and used for the hybrid optical link. A performance analysis [...] Read more.
In this paper, we propose, design, and evaluate a new hybrid terrestrial–underwater optical communication link for providing high-speed connectivity between land and underwater systems. A device based on an amplify-and-forward strategy is considered and used for the hybrid optical link. A performance analysis of the proposed hybrid system is then carried out, taking into account both the atmospheric and underwater channels and their respective degradation sources. Different networking scenarios and conditions are evaluated. To this end, the channel model of the terrestrial free-space optical (FSO) link is modeled using the Gamma–Gamma distribution, while the underwater optical link is modeled using the Weibull distribution. The former takes into account atmospheric and turbulence attenuation, geometric spread and pointing errors, while the latter takes into account underwater and turbulence attenuation and geometric spread. Accordingly, a new analytical closed-form expression for the bit error rate (BER), which depends on the cumulative distribution function of the holistic hybrid system, is derived. Analytical results show that pointing errors as well as atmospheric and oceanic turbulence seriously degrade the performance of the hybrid system. In addition, ocean turbulence leads to the occurrence of a BER floor in some scenarios. This is the first time that such a network is proposed and modeled under the assumption of critical channel impairments. Full article
(This article belongs to the Special Issue Free-Space Optical Communication: Physics and Applications)
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12 pages, 5876 KiB  
Article
Online Denoising Single-Pixel Imaging Using Filtered Patterns
by Zhaohua Yang, Xiang Chen, Zhihao Zhao, Lingan Wu and Yuanjin Yu
Photonics 2024, 11(1), 59; https://doi.org/10.3390/photonics11010059 - 5 Jan 2024
Cited by 1 | Viewed by 1740
Abstract
Noise is inevitable in single-pixel imaging (SPI). Although post-processing algorithms can significantly improve image quality, they introduce additional processing time. To address this issue, we propose an online denoising single-pixel imaging scheme at the sampling stage, which uses the filter to optimize the [...] Read more.
Noise is inevitable in single-pixel imaging (SPI). Although post-processing algorithms can significantly improve image quality, they introduce additional processing time. To address this issue, we propose an online denoising single-pixel imaging scheme at the sampling stage, which uses the filter to optimize the illumination modulation patterns. The image is retrieved through the second-order correlation between the modulation patterns and the intensities detected by the single-pixel detector. Through simulations and experiments, we analyzed the impact of sampling rate, noise intensity, and filter template on the reconstructed images of both binary and grayscale objects. The results demonstrate that the denoising effect is comparable to the imaging-first followed by post-filtering procedures, but the post-processing time is reduced for the same image quality. This method offers a new way for rapid denoising in SPI, and it should be particularly advantageous in applications where time-saving is of paramount importance, such as in image-free large target classification. Full article
(This article belongs to the Special Issue Advances in Photonic Materials and Technologies)
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22 pages, 29853 KiB  
Article
Investigation of OFDM-Based HS-PON Using Front-End LiFiSystem for 5G Networks
by Meet Kumari, Mai Banawan, Vivek Arya and Satyendra Kumar Mishra
Photonics 2023, 10(12), 1384; https://doi.org/10.3390/photonics10121384 - 16 Dec 2023
Cited by 14 | Viewed by 2637
Abstract
Fifth-generation (5G) technology has enabled faster communication speeds, lower latency, a broader range of coverage, and greater capacity. This research aims to introduce a bidirectional high-speed passive optical network (HS-PON) for 5G applications and services including mobile computing, cloud computing, and fiber wireless [...] Read more.
Fifth-generation (5G) technology has enabled faster communication speeds, lower latency, a broader range of coverage, and greater capacity. This research aims to introduce a bidirectional high-speed passive optical network (HS-PON) for 5G applications and services including mobile computing, cloud computing, and fiber wireless convergence. Using 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing techniques, the system transmits uplinks and downlinks with a pair of four wavelengths each. Light fidelity (LiFi) services are provided with blue light-emitting-diode-based technology. With a threshold bit error rate (BER) of 10−3, the results demonstrate reliable transportation over a 100 km fiber at −17 dBm received power and in a maximum LiFi range of 20 m. Furthermore, the system offers symmetric 4 × 50 Gbps transmission rates under the impact of fiber–LiFi channel impairments with maximum irradiance and incidence half-angles of 500. Additionally, at threshold BER, the system provides a detection surface range from 1.5 to 4 cm2. Compared to existing networks, the system also provides a high gain and low noise figure. A number of features make this system an attractive option. These include its high speed, high reach, high split ratio, low cost, easy upgradeability, pay-as-you-grow properties, high reliability, and ability to accommodate a large number of users. Full article
(This article belongs to the Special Issue Optical Technologies Supporting 5G/6G Mobile Networks)
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8 pages, 5646 KiB  
Article
Mode-Independent Optical Switch Based on Graphene-Polymer Hybrid Waveguides
by Tianhang Lian, Yuhang Xie, Qidong Yu, Shijie Sun, Xiaoqiang Sun, Xibin Wang and Daming Zhang
Photonics 2023, 10(12), 1372; https://doi.org/10.3390/photonics10121372 - 13 Dec 2023
Cited by 1 | Viewed by 1586
Abstract
Mode-division multiplexing (MDM) is a promising multiplexing technique to further improve the transmission capacity of optical communication and on-chip optical interconnection systems. Furthermore, the multimode optical switch is of great importance in the MDM system, since it makes the MDM system more flexible [...] Read more.
Mode-division multiplexing (MDM) is a promising multiplexing technique to further improve the transmission capacity of optical communication and on-chip optical interconnection systems. Furthermore, the multimode optical switch is of great importance in the MDM system, since it makes the MDM system more flexible by directly switching multiple spatial signals simultaneously. In this paper, we proposed a mode-independent optical switch based on the graphene–polymer hybrid waveguide platform that could process the TE11, TE12, TE21 and TE22 modes in a few-mode waveguide. The presented switch is independent of the four guided modes, optimizing the buried position of graphene capacitors in the polymer waveguide to regulate the coplanar interaction between the graphene capacitors and spatial modes. The TE11, TE12, TE21 and TE22 modes can be regulated simultaneously by changing the chemical potential of graphene capacitors in a straight waveguide. Our presented switch can enable the independent management of the spatial modes to be more flexible and efficient and has wide application in the MDM transmission systems. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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11 pages, 3191 KiB  
Article
Ultra-Broadband, Compact Arbitrary-Ratio Multimode Power Splitter Based on Tilted Subwavelength Gratings
by Wenbin Chen, Hongjie Guo, Yongkang Yang, Baiang Qu, Yali Zhao, Yingchun Cao, Wentao Guo and Manqing Tan
Photonics 2023, 10(12), 1327; https://doi.org/10.3390/photonics10121327 - 29 Nov 2023
Cited by 2 | Viewed by 1773
Abstract
Mode division multiplexing (MDM) technology is an effective solution for high-capacity optical interconnection, and multimode power splitters, as essential components in MDM systems, have attracted widespread attention. However, supporting a wide range of modes and arbitrary power splitting ratios with large bandwidth in [...] Read more.
Mode division multiplexing (MDM) technology is an effective solution for high-capacity optical interconnection, and multimode power splitters, as essential components in MDM systems, have attracted widespread attention. However, supporting a wide range of modes and arbitrary power splitting ratios with large bandwidth in power splitters remains a significant challenge. In this paper, we designed a power splitter based on a subwavelength grating (SWG) structure with tilted placement on a silicon-on-insulator (SOI) substrate. We achieve arbitrary TE0–TE9 mode-insensitive power distribution by altering the filling coefficient of the SWG. Thanks to our specific selection of cladding materials and compensatory design for the optical wave transmission and reflection shifts induced by SWG, our device demonstrates low additional loss (EL < 1.1 dB) and inter-mode crosstalk (−18.8 < CT < −60 dB) for optical modes ranging from TE0 to TE9, covering a wavelength range from 1200 nm to 1700 nm. Furthermore, our proposed device can be easily extended to higher-order modes with little loss of device performance, offering significant potential in MDM platforms. Full article
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17 pages, 7012 KiB  
Article
Foundry-Processed Compact and Broadband Adiabatic Optical Power Splitters with Strong Fabrication Tolerance
by Can Ozcan, J. Stewart Aitchison and Mo Mojahedi
Photonics 2023, 10(12), 1310; https://doi.org/10.3390/photonics10121310 - 27 Nov 2023
Cited by 6 | Viewed by 2310
Abstract
Optical power splitters play a crucial role as the fundamental building blocks for many integrated optical devices. They should have low losses, a broad bandwidth, and a high tolerance to fabrication errors. Adiabatic optical power splitters inherently possess these qualities while being compatible [...] Read more.
Optical power splitters play a crucial role as the fundamental building blocks for many integrated optical devices. They should have low losses, a broad bandwidth, and a high tolerance to fabrication errors. Adiabatic optical power splitters inherently possess these qualities while being compatible with foundry processes well suited for mass production. The long device lengths of adiabatic power splitters, however, are a limiting factor to achieve compact device sizes, which must be reduced. Here, we used a polynomial taper profile optimization algorithm to design 1 × 2 and 2 × 2 adiabatic power splitters with significantly shorter lengths than their adiabatic counterparts. The best-performing 1 × 2 and 2 × 2 power splitters had 20 μm and 16 μm coupling lengths, respectively. Our designs had minimum feature sizes ranging from 140 nm to 200 nm, and our measurements averaged across nine different chips showed excellent consistency in performance for devices with 180 nm and 200 nm minimum features. Both the 1 × 2 and 2 × 2 adiabatic optical power splitters had excess losses less than 0.7 dB over a 100 nm bandwidth, with a standard deviation lower than 0.3 dB. Furthermore, our measurements showed splitting ratios within 50 ± 3% over a 130 nm bandwidth. We also demonstrated the design of 1 × 2 power splitters with arbitrary splitting ratios, where splitting ratios ranging from 50:50 to 94:6 were achieved with standard deviations between 2% and 6%. Full article
(This article belongs to the Special Issue On-Chip Photonics)
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17 pages, 6018 KiB  
Article
Dynamic Secure Key Distribution Based on Dispersion Equalization and Cellular Automata for Optical Transmission
by Jiabin Cui, Wei Kong, Zhaoyang Liu and Yuefeng Ji
Photonics 2023, 10(12), 1308; https://doi.org/10.3390/photonics10121308 - 27 Nov 2023
Viewed by 1920
Abstract
This paper proposes a dynamic secure key distribution scheme based on dispersion equalization and cellular automata (CAs). The scheme effectively eliminates the key inconsistency problem caused by imperfect channel reciprocity, and dynamic key sequences can be conveniently generated with large key space in [...] Read more.
This paper proposes a dynamic secure key distribution scheme based on dispersion equalization and cellular automata (CAs). The scheme effectively eliminates the key inconsistency problem caused by imperfect channel reciprocity, and dynamic key sequences can be conveniently generated with large key space in long-haul optical transmission. In the process of communication, the legitimate parties obtain the secure core parameter from the frequency domain equalizer algorithm, and a final key sequence is generated through CA iterations on the basis of the core parameter. The randomness and reciprocity characteristics of the channel ensure the security and uniqueness of the core parameter and final key sequence. With 10G Baud 16 quadrature amplitude modulation over 400 km standard single-mode fiber transmission, the proposed scheme is verified with a free key error rate and an unlimited key generation rate. The security robustness of this scheme was theoretically analyzed and verified by sweeping the eavesdropper’s tapping position and improving CA operation processing. The proposed key distribution scheme is compatible with the existing transmission system for different signal modulation formats. Full article
(This article belongs to the Special Issue Optical Communication, Sensing and Network)
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12 pages, 10146 KiB  
Communication
Effect of Beam-Steering Angle, Operation Wavelength and Mean Inter-Element Distance on the Side-Lobe Levels of Integrated Optical Phased Arrays under Beam-Steering Operation
by Ivan Aldaya, Bruna Dias Pires de Souza, Rafael Abrantes Penchel, Julian Leonel Pita, Mirian Paula dos Santos, José Augusto de Oliveira and Marcelo Luis Francisco Abbade
Photonics 2023, 10(12), 1300; https://doi.org/10.3390/photonics10121300 - 24 Nov 2023
Cited by 2 | Viewed by 1982
Abstract
Integrated optical phased arrays (OPAs) play an important role in a broad range of applications. Fabrication constraints, however, pose a limit to the minimum inter-element separation that further results in high-intensity side lobes. The intensity of these secondary lobes can be reduced by [...] Read more.
Integrated optical phased arrays (OPAs) play an important role in a broad range of applications. Fabrication constraints, however, pose a limit to the minimum inter-element separation that further results in high-intensity side lobes. The intensity of these secondary lobes can be reduced by arranging the antenna elements with non-uniform separation distance, which has been addressed by different methods. In this paper we employ one of the already proven optimization algorithms, i.e., differential evolution, to optimize the element positions of linear arrays with different configurations operating under beam-steering operation and considering a minimum inter-element distance. These optimizations allowed us to derive some design guidelines that can assist in reducing the side-lobe level (SLL) of integrated linear OPAs. In particular, we found that it is necessary to optimize the positions for the broadest beam-steering angle and the shortest operation wavelength. Additionally, optimizations of different configurations reveal that, when imposing a minimum inter-element distance, there is an optimum mean distance that minimizes the SLL of the array. Full article
(This article belongs to the Special Issue Optical Wireless Communications and Applications)
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14 pages, 2278 KiB  
Review
Recent Advances in Graphene-Enabled Silicon-Based High-Speed Optoelectronic Devices—A Review
by Yadvendra Singh and Harish Subbaraman
Photonics 2023, 10(12), 1292; https://doi.org/10.3390/photonics10121292 - 23 Nov 2023
Cited by 5 | Viewed by 3732
Abstract
Silicon (Si) photonics has emerged as a prominent technology for meeting the escalating requirements of high-speed data transmission in optical communication systems. These systems need to be compact, energy-efficient, and capable of handling large amounts of data, driven by the advent of next-generation [...] Read more.
Silicon (Si) photonics has emerged as a prominent technology for meeting the escalating requirements of high-speed data transmission in optical communication systems. These systems need to be compact, energy-efficient, and capable of handling large amounts of data, driven by the advent of next-generation communication devices. Recently, there have been significant activities in exploring graphene within silicon-based components to enhance the overall performance metrics of optoelectronic subsystems. Graphene’s high mobility of charge carriers makes it appealing for the next generation of high-performance devices, especially in high-speed optoelectronics. However, due to its zero bandgap, graphene is unlikely to replace silicon entirely, but it exhibits potential as a catalyst for silicon-based devices, namely in high-speed electronics and optical modulators, where its distinctive characteristics can facilitate progress in silicon photonics and other fields. This paper aims to provide an objective review of the advances made within the realm of graphene-integrated Si photonics for high-speed light modulation and detection. Full article
(This article belongs to the Special Issue On-Chip Photonics)
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13 pages, 3905 KiB  
Article
Theoretical Substantiation of the Possibility of Performing Non-Damaging UV Diagnostics of Biological Tissues In Vivo
by Andrey P. Tarasov, Maria E. Shtyflyuk and Dmitry A. Rogatkin
Photonics 2023, 10(12), 1289; https://doi.org/10.3390/photonics10121289 - 22 Nov 2023
Cited by 4 | Viewed by 1158
Abstract
Since UV radiation is capable of causing skin erythema, there is a risk of damage during in vivo UV spectroscopy of skin. In particular, the conventional estimation of radiation dose indicates the impossibility of conducting such studies when using fiber sources to deliver [...] Read more.
Since UV radiation is capable of causing skin erythema, there is a risk of damage during in vivo UV spectroscopy of skin. In particular, the conventional estimation of radiation dose indicates the impossibility of conducting such studies when using fiber sources to deliver UVA and UVB radiation to the skin due to the rapid accumulation of the minimal erythema dose (MED). Using numerical simulations, we investigated the possibility of achieving MED when exposing the skin to UV light of diagnostic power and forming irradiation spots of different sizes. It has been shown that the conventional approach to calculating the dose as radiant exposure (J/cm2) turns out to be unsuitable in the case of irradiation spots of small area (which is the case when fiber sources are used) since it greatly overestimates the dose. This, in turn, results in a significant underestimation of the permissible duration of the diagnostic procedure. The reason for this is the failure to take into account the diffusion of radiation in biological tissue. We substantiated that for a more correct calculation of the dose taking into account diffusion, it is necessary to estimate the volumetric energy density (J/cm3) in biological tissue. In vivo experiments confirmed that this approach is more correct in determining the time to reach erythema compared to the conventional approach. The calculations showed that the minimum spot area of UVA/UVB irradiation on the skin surface, beyond which the calculation of the dose as radiant exposure does not introduce a significant error, is 1.5–3 mm2, which corresponds to diameters of 1.4–2 mm in the case of a round irradiation spot. Full article
(This article belongs to the Special Issue Biomedical Spectroscopy: Techniques and Applications)
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18 pages, 5108 KiB  
Article
Investigations of Nanoscale Columnar AlxGa1-xN/AlN Heterostructures Grown on Silicon Substrates with Different Modifications of the Surface
by Pavel Vladimirovich Seredin, Nikolay Kurilo, Dmitry L. Goloshchapov, Vladimir Kashkarov, Aleksandr S. Lenshin, Nikita Buylov, Dmitry Nesterov, Andrey Mizerov, Sergey A. Kukushkin, S. Timoshnev, K. Yu. Shubina and M. S. Sobolev
Photonics 2023, 10(11), 1209; https://doi.org/10.3390/photonics10111209 - 30 Oct 2023
Viewed by 1319
Abstract
The growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on the surface of silicon substrates using plasma-activated nitrogen molecular-beam epitaxy was investigated in this work. Silicon substrates include atomic-smooth cSi substrate, Si substrate with a transition layer of porous silicon porSi/cSi [...] Read more.
The growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on the surface of silicon substrates using plasma-activated nitrogen molecular-beam epitaxy was investigated in this work. Silicon substrates include atomic-smooth cSi substrate, Si substrate with a transition layer of porous silicon porSi/cSi and a hybrid substrate involving a silicon carbide layer grown with matched substitution of the atoms on the surface of porous silicon SiC/porSi/cSi. A complex analysis performed using a set of structural and spectroscopic techniques demonstrated that the epitaxial growth of the nuclear AlN layer on all types of the substrates in a N-enriched environment resulted in the formation of AlxGa1-xN/AlN heterostructures with a Ga-polar surface, which was realized only on the SiC/porSi/cSi substrate. The layer of AlxGa1-xN on cSi and porSi/cSi substrates was in the state of disordered alloy with an excess of gallium atom content. It was shown that a great difference in the lattice parameters of a substrate–film pair resulted not only in the appearance of a number of various defects but also in a considerable effect on the chemical process of the formation of the alloys, in our case, the AlxGa1-xN alloy. It was shown that nanoscale columns of AlxGa1-xN formed on SiC/porSi/cSi substrate were inclined relative to the c-axis, which was connected with the features of the formation of a SiC layer by the matched substitution of the atoms on the porous Si substrate, resulting in the formation of the inclined (111) SiC facets at the boundary of the (111) Si surface and pores in Si. Optical studies of the grown samples demonstrated that the optical band-to-band transition for the AlxGa1-xN alloy with Eg = 3.99 eVB was observed only for the heterostructure grown on the SiC/porSi/cSi substrate. A qualitative model is proposed to explain the difference in the formation of AlxGa1-xN layers on the substrates of cSi, porSi/cSi and SiC/porSi/cSi. The results obtained in our work demonstrate the availability of using SiC/porSi/cSi substrates for the integration of silicon technology and that used for the synthesis of nanoscale columnar AlxGa1-xN heterostructures using plasma-activated molecular-beam epitaxy with a nitrogen source. Full article
(This article belongs to the Special Issue III-V Semiconductors Optoelectronic Materials and Devices)
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9 pages, 1280 KiB  
Article
Genetic Optimization of the Y-Shaped Photonic Crystal NOT Logic Gate
by Vladimir Pavelyev, Yuliana Krivosheeva and Dimitriy Golovashkin
Photonics 2023, 10(10), 1173; https://doi.org/10.3390/photonics10101173 - 21 Oct 2023
Cited by 2 | Viewed by 1889
Abstract
The present paper is devoted to the actual problem of photonic crystal (PhC) logic gate design. The development of components for photonic digital computing systems will provide opportunities for high-efficient information processing. The use of 2D photonic crystals is one of the most [...] Read more.
The present paper is devoted to the actual problem of photonic crystal (PhC) logic gate design. The development of components for photonic digital computing systems will provide opportunities for high-efficient information processing. The use of 2D photonic crystals is one of the most promising approaches to designing interference logic gates. Photonic crystal band gap and use of lattice defects are giving opportunities for flexible control of waveguiding light. Interference logic gates of NOT, OR, AND, and XOR types based on the Y-shaped structure are well known. However, known realizations have limited energy efficiency. Earlier, a method for minimizing energy losses at the PhC waveguide bending based on genetic optimization of the PhC waveguide topology was proposed and investigated. In this paper, the genetic algorithm for optimization of the PhC interference logic gate of the NOT type was used. Optimization of the Y-shaped topology allowed for an increase in the energy efficiency of the logic gate to 95%. A description of the developed numerical procedure as well as computer simulation results are presented. The developed procedure includes the possibility of taking into account the limitations of the technology to be used for the realization of a designed 2D PhC structure. Full article
(This article belongs to the Special Issue Recent Advances in Diffractive Optics)
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35 pages, 12619 KiB  
Review
Polarization Lidar: Principles and Applications
by Xudong Liu, Liping Zhang, Xiaoyu Zhai, Liye Li, Qingji Zhou, Xue Chen and Xiaobo Li
Photonics 2023, 10(10), 1118; https://doi.org/10.3390/photonics10101118 - 4 Oct 2023
Cited by 30 | Viewed by 10154
Abstract
Traditional lidar techniques mainly rely on the backscattering/echo light intensity and spectrum as information sources. In contrast, polarization lidar (P-lidar) expands the dimensions of detection by utilizing the physical property of polarization. By incorporating parameters such as polarization degree, polarization angle, and ellipticity, [...] Read more.
Traditional lidar techniques mainly rely on the backscattering/echo light intensity and spectrum as information sources. In contrast, polarization lidar (P-lidar) expands the dimensions of detection by utilizing the physical property of polarization. By incorporating parameters such as polarization degree, polarization angle, and ellipticity, P-lidar enhances the richness of physical information obtained from target objects, providing advantages for subsequent information analysis. Over the past five decades, the application fields of P-lidar have rapidly expanded, starting from its early use in atmospheric remote sensing to later applications in oceanic remote sensing. This review first provides a brief introduction to the basic principles of both polarization and P-lidar, along with typical systems. It then explores the applications of P-lidar in various remote sensing fields, including atmospheric, oceanic, and terrestrial domains. Additionally, we propose potential research directions based on current cutting-edge applications, with the aims of providing critical insights to researchers in the fields of polarization and lidar and inspiring further exciting ideas. Full article
(This article belongs to the Special Issue Advanced Polarimetry and Polarimetric Imaging)
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11 pages, 9874 KiB  
Article
Optimizing Self-Seeded Perfluorooctane SBS Compressor Configurations to Achieve ~90 ps High-Energy Pulses
by Aleksej M. Rodin, Augustė Černeckytė, Paulius Mackonis and Augustinas Petrulėnas
Photonics 2023, 10(9), 1060; https://doi.org/10.3390/photonics10091060 - 20 Sep 2023
Cited by 2 | Viewed by 1811
Abstract
Three different stimulated Brillouin scattering (SBS) configurations in perfluorooctane were experimentally compared to achieve the ultimate compression of ~1.1 ns pulses from a commercially available Nd:YAG mini-laser. These schemes contained either a focusing lens and a plane feedback mirror, a spherical mirror, or [...] Read more.
Three different stimulated Brillouin scattering (SBS) configurations in perfluorooctane were experimentally compared to achieve the ultimate compression of ~1.1 ns pulses from a commercially available Nd:YAG mini-laser. These schemes contained either a focusing lens and a plane feedback mirror, a spherical mirror, or variable pulse splitting to provide self-seeding of the SBS. In the optimal configuration with a focusing lens and return mirror, 93 ps pulses with an energy of 9.5 mJ were achieved at the output of the double-pass phase-conjugated Nd:YAG amplifier. The resulting diffraction-free, high-quality beams with M2~1.2 and excellent pointing stability are of practical interest for scientific, medical, and industrial applications. Full article
(This article belongs to the Special Issue Photonics: Theory, Technologies and Applications)
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11 pages, 2657 KiB  
Article
High-Linear Frequency-Swept Lasers with Data-Driven Control
by Haohao Zhao, Dachao Xu, Zihan Wu, Liang Sun, Guohui Yuan and Zhuoran Wang
Photonics 2023, 10(9), 1056; https://doi.org/10.3390/photonics10091056 - 18 Sep 2023
Cited by 1 | Viewed by 1946
Abstract
The frequency-swept laser (FSL) is applied widely in various sensing systems in the scientific and industrial fields, especially in the light detection and ranging (Lidar) area. However, the inherent nonlinearity limits its performance in application systems, especially in the broadband frequency-swept condition. In [...] Read more.
The frequency-swept laser (FSL) is applied widely in various sensing systems in the scientific and industrial fields, especially in the light detection and ranging (Lidar) area. However, the inherent nonlinearity limits its performance in application systems, especially in the broadband frequency-swept condition. In this work, from the perspective of data-driven control, we adopt the reinforcement learning-based broadband frequency-swept linearization method (RL-FSL) to optimize the control policy and generate the modulation signals. The nonlinearity measurement system and the system simulator are established. Since the powerful learning ability of the reinforcement learning algorithm, the linearization policy is optimized off-line and the generated modulation signals reduce the nonlinearity almost 20 times, compared to the case without control. In the long-term operation, the regular updated modulation signals perform better than the traditional iteration results, demonstrating the efficiency of the proposed data-driven control method in application systems. Therefore, the RL-FSL method has the potential to be the candidate of optical system control. Full article
(This article belongs to the Special Issue Artificial Intelligence and Machine Learning in Photonics)
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12 pages, 4493 KiB  
Article
Structurally Stable Astigmatic Vortex Beams with Super-High Orbital Angular Momentum (ABCD Matrix Approach)
by Alexander Volyar, Mikhail Bretsko, Server Khalilov and Yana Akimova
Photonics 2023, 10(9), 1048; https://doi.org/10.3390/photonics10091048 - 15 Sep 2023
Cited by 5 | Viewed by 1871
Abstract
We have demonstrated efficiency of employing the ABCD matrix approach to transform higher-order structured Laguerre–Gaussian (sLG) beams into structurally stable astigmatic sLG (asLG) beams, highlighting their dynamics at propagating. Radical transformations of the beam structure by a cylindrical lens form not only orbital [...] Read more.
We have demonstrated efficiency of employing the ABCD matrix approach to transform higher-order structured Laguerre–Gaussian (sLG) beams into structurally stable astigmatic sLG (asLG) beams, highlighting their dynamics at propagating. Radical transformations of the beam structure by a cylindrical lens form not only orbital angular momentum (OAM) fast oscillations and bursts, but also make the asLG beams structurally unstable in propagation through cylindrical and spherical lenses when focusing paraxially. But, if the spherical lens performs a Fourier transform of the asLG beam after a cylindrical lens, the symmetric beam emerges at the lens focal plane with a sharp OAM dip; then, the OAM restores its former astigmatism, becoming structurally stable at the far diffraction domain. By investigating the beam structure at the focal area, we have showed that the OAM sharp dip is associated with nothing less than the process of dividing the OAM into the vortex and astigmatic constitutes predicted by Anan’ev and Bekshaev. Full article
(This article belongs to the Special Issue Advances and Application of Structured Light)
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8 pages, 1480 KiB  
Communication
High-Responsivity Planar Photodetector Based on Methylammonium Lead Bromide Perovskite Thin Film
by Pavlo Mai, Julien Houel, Nathan Dreveton, Benoit Mahler and Alban Gassenq
Photonics 2023, 10(9), 1043; https://doi.org/10.3390/photonics10091043 - 14 Sep 2023
Cited by 2 | Viewed by 5997
Abstract
We have fabricated planar interdigitated photodetectors exhibiting high responsivity. These detectors are based on thin layers of methylammonium lead bromide (MAPbBr3) at 90 nm thickness. MAPbBr3 thin films were first characterized on glass (borosilicate) substrates using absorption and photoluminescence measurements [...] Read more.
We have fabricated planar interdigitated photodetectors exhibiting high responsivity. These detectors are based on thin layers of methylammonium lead bromide (MAPbBr3) at 90 nm thickness. MAPbBr3 thin films were first characterized on glass (borosilicate) substrates using absorption and photoluminescence measurements showing a high absorption edge at 521 nm and strong emission at 530 nm, as expected. MAPbBr3 thin films were then deposited on top of interdigitated electrodes, hence producing planar photodetectors with responsivity up to 0.4 A/W. Such higher performances were attributed to the interdigitated design, low crack density (0.05 µm−2), and lower resistivity (20 MΩ.cm) compared to MAPbBr3 single crystal. Therefore, this work highlights MAPbBr3 thin films as very promising for photodetection applications. Full article
(This article belongs to the Special Issue Perovskite Materials and Optoelectronic Applications)
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15 pages, 4860 KiB  
Article
Gyrotropic Crystals as a Basis for Creation of Helical Polychromatic Singular Beams
by Yuriy Egorov and Alexander Rubass
Photonics 2023, 10(9), 1044; https://doi.org/10.3390/photonics10091044 - 14 Sep 2023
Cited by 6 | Viewed by 1627
Abstract
In this work, studies are carried out in the field of optical singular beams that have passed through gyrotropic crystals. We have experimentally shown that singular beams with a helical intensity distribution are formed when passing through a system of two gyrotropic crystals [...] Read more.
In this work, studies are carried out in the field of optical singular beams that have passed through gyrotropic crystals. We have experimentally shown that singular beams with a helical intensity distribution are formed when passing through a system of two gyrotropic crystals with opposite values of the gyration coefficient. It is shown that the system is capable of generating optical vortices with a double topological charge in one of the components of circular polarization when light propagates through two gyrotropic crystals. Full article
(This article belongs to the Special Issue Optical Communication, Sensing and Network)
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17 pages, 7013 KiB  
Article
Design and Implementation of a Non-Common-View Axis Alignment System for Airborne Laser Communication
by Chenghu Ke, Yuting Shu, Xizheng Ke, Meimiao Han and Ruidong Chen
Photonics 2023, 10(9), 1037; https://doi.org/10.3390/photonics10091037 - 11 Sep 2023
Cited by 3 | Viewed by 2098
Abstract
This paper proposes a non-common-view axis alignment method for the alignment requirements of airborne laser communication systems. The system consists of a ground transmitting end and an airborne relay terminal. The ground transmitting end uses a camera and a pan-tilt for image tracking, [...] Read more.
This paper proposes a non-common-view axis alignment method for the alignment requirements of airborne laser communication systems. The system consists of a ground transmitting end and an airborne relay terminal. The ground transmitting end uses a camera and a pan-tilt for image tracking, while the airborne relay end uses a two-dimensional mirror to control the beam to achieve non-common-view axis alignment between the transmitting and receiving sides. The working principle and process of both the transmitter and receiver of the non-common-view axis alignment system for airborne laser communication were compared with traditional wireless optical alignment methods. The design process of the two-dimensional mirror used in this paper is introduced, the scanning trajectory of the two-dimensional mirror is simulated and analyzed according to the beam scanning principle, and the field experiment link is set up to carry out the airborne laser communication experiment. The experimental results show that when the link distance is 10 m, the tracking errors of the system in the azimuth and pitch directions are 19.02 µrad and 22.35 µrad respectively, and the amplitude of the electrical signal output by the signal detector is 84.0 mV; When the link distance is 20 m, the tracking errors of the system in the azimuth and pitch directions are 39.66 µrad and 33.94 µrad respectively, and the amplitude of the electrical signal output by the signal detector is 23.0 mV. Using this method, the alignment can be completed without data return, and the establishment of the reverse link can also be realized while the transmission link is quickly established, and there is no need for an air stability platform. The feasibility of the application of the non-common-view axis alignment method to the airborne laser communication system is verified. Full article
(This article belongs to the Special Issue Application of Adaptive Optics Theory and Technology in Optical Wireless Communication)
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9 pages, 3147 KiB  
Communication
Inverse Design of Ultra-Compact and Low-Loss Optical Phase Shifters
by Junpeng Liao, Ye Tian, Zhe Kang and Xiaowei Zhang
Photonics 2023, 10(9), 1030; https://doi.org/10.3390/photonics10091030 - 8 Sep 2023
Cited by 2 | Viewed by 2207
Abstract
In previous works, inverse design methods have primarily focused on manipulating the optical power to achieve specific design targets. In this paper, we use the inverse design method to enable the precise engineering of the optical phase. As a proof of concept, we [...] Read more.
In previous works, inverse design methods have primarily focused on manipulating the optical power to achieve specific design targets. In this paper, we use the inverse design method to enable the precise engineering of the optical phase. As a proof of concept, we present a series of phase shifters (PSs) with varying phase shifts, which are inversely designed and theoretically validated on the silicon-on-insulator (SOI) platform. The designed PSs exhibit remarkable accuracy, with deviations of below 1°. These proposed PSs feature an ultra-compact footprint of 3 µm in length and offer superior fabrication tolerances compared to conventional structures. Over the 1535–1565 nm bandwidth, the discrepancy between the actual and target phase shifts remains below ±1° for all phase shifters, while the insertion loss is consistently below 0.035 dB. Moreover, the feasibility of the designed five PSs is verified using 2 × 2 multimode interference couplers (MMI). Full article
(This article belongs to the Special Issue Silicon and Silicon Nitride Integrated Photonics: Challenges and Opportunities)
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12 pages, 750 KiB  
Article
Optical Bistability and Thermal Mode Hopping in External Cavity Feedback Semiconductor Lasers
by Da Meng, Haiyang Yu, Yejin Zhang and Jianguo Liu
Photonics 2023, 10(9), 1027; https://doi.org/10.3390/photonics10091027 - 8 Sep 2023
Cited by 6 | Viewed by 2220
Abstract
The external cavity feedback semiconductor laser shows obvious optical bistability in practice. That is, at the same operating temperature, different temperature tuning directions will lead to different laser mode outputs. This will lead to optical mode hopping and unstable output wavelength of the [...] Read more.
The external cavity feedback semiconductor laser shows obvious optical bistability in practice. That is, at the same operating temperature, different temperature tuning directions will lead to different laser mode outputs. This will lead to optical mode hopping and unstable output wavelength of the laser. In this work, we measured this phenomenon and explained it through a theoretical model with thermal synchronization considered. Our measured results show obvious bistability and temperature tuning direction dependence. In order to explain this phenomenon, we considered the physical characteristics of each optoelectronic component in the external cavity, and found that the temperature changes of each component were not synchronized over time. After establishing a model that takes into account the thermal asynchrony phenomenon, we have effectively explained this phenomenon. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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12 pages, 7172 KiB  
Article
Imaging through a Scattering Medium under Different Intensities of Ambient Light Interference
by Yantong Zhang, Huiling Huang, Feibin Wu, Jun Han, Yi Yang and Ruyi Li
Photonics 2023, 10(9), 1023; https://doi.org/10.3390/photonics10091023 - 7 Sep 2023
Cited by 3 | Viewed by 2075
Abstract
Many solutions for imaging through a scattering medium are sensitive to noise, which can lead to degradation or even to a failure of the image quality. This is especially the case in practical application scenarios, which are always filled with changing ambient light [...] Read more.
Many solutions for imaging through a scattering medium are sensitive to noise, which can lead to degradation or even to a failure of the image quality. This is especially the case in practical application scenarios, which are always filled with changing ambient light interference; as such, the traditional methods are difficult to practically apply. Therefore, in this paper, a spatial-frequency dual-domain learning neural network is designed for reconstructing the target of a speckle pattern under different intensities of ambient light interference. The network is mainly based on two modules. One module is designed from two perspectives, frequency domain denoising and the spatial-frequency spectrum of the speckle pattern. Another module is a dual-feature fusion attention module, which is used to improve the accuracy of the network. The experimental results demonstrate that the network is capable of reconstructing complex targets with high quality under varying intensities of interfering light. Furthermore, it is not constrained by the optical memory effect, exhibiting remarkable robustness and generalizability. The research based on this paper provides a feasible path for the practical application of scattering imaging methods. Full article
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21 pages, 5976 KiB  
Review
Functionalized Chiral Twisted Optical Fibers: A Review
by Yifan Zhang, Boyao Li, Tianrong Huang, Guiyao Zhou and Yaoyao Liang
Photonics 2023, 10(9), 1025; https://doi.org/10.3390/photonics10091025 - 7 Sep 2023
Cited by 1 | Viewed by 2503
Abstract
With an increase in the volume of information exchange and perception, the demands for intelligent, miniaturized, and integrated optical devices for information acquisition are also increasing. As the core component of optical networks for transmitting information, further optimization of their structural characteristics to [...] Read more.
With an increase in the volume of information exchange and perception, the demands for intelligent, miniaturized, and integrated optical devices for information acquisition are also increasing. As the core component of optical networks for transmitting information, further optimization of their structural characteristics to generate richer optical characteristics and apply them to information exchange and optical field control has become a key research hotspot. The introduction of chiral twist characteristics has led to new phenomena and applications in optical field transmission and the transformation of traditional optical fibers or microstructured optical fibers (MOF). Therefore, this review mainly begins with the principle of chiral optical fibers, introduces their preparation and latest application scenarios, and finally discusses their potential future development prospects. Full article
(This article belongs to the Special Issue Mechanisms, Applications and Development of Microstructure-Based Fiber Devices)
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