Vacuum Research Articles

Symbol detection and BER analysis in wireless and free space optical networks using low complexity neural equalizer

Symbol detection and BER analysis in wireless and free space optical networks using low complexity neural equalizer

High-Gain Miniaturized Multi-Band MIMO SSPP LWA for Vehicular Communications

This paper introduces a novel miniaturized, four-mode, semi-flexible leaky wave Multiple-Input Multiple-Output (MIMO) antenna specifically designed to advance vehicular communication systems. The proposed antenna addresses key challenges in 5G low- and high-frequency bands, including millimeter-wave communication, by integrating innovative features such as a periodic Spoof Surface Plasmon Polariton Transmission Line (SSPP-TL) and logarithmic-spiral-like semi-circular strip patches parasitically fed via orthogonal ports. These design elements facilitate stable impedance matching and wide impedance bandwidths across operating bands, which is essential for vehicular networks. The hybrid combination of leaky wave and SSPP structures, along with a defected wide-slot ground structure and backside meander lines, enhances radiation characteristics by reducing back and bidirectional radiation. Additionally, a naturalization network incorporating chamfered-edge meander lines minimizes mutual coupling and introduces a fourth radiation mode at 80 GHz. Compact in size (14 × 12 × 0.25 mm3), the antenna achieves high-performance metrics, including S11 < −18.34 dB, dual-polarization, peak directive gains of 11.6 dBi (free space) and 14.6 dBi (on vehicles), isolation > 27 dB, Channel Capacity Loss (CCL) < 3, Envelope Correlation Coefficient (ECC) < 0.001, axial ratio < 2.25, and diversity gain (DG) > 9.85 dB. Extensive testing across various vehicular scenarios confirms the antenna’s robustness for Vehicle-to-Vehicle (V2V), Vehicle-to-Pedestrian (V2P), and Vehicle-to-Infrastructure (V2I) communication. Its exceptional performance ensures seamless connectivity with mobile networks and enhances safety through Specific Absorption Rate (SAR) compliance. This compact, high-performance antenna is a transformative solution for connected and autonomous vehicles, addressing critical challenges in modern automotive communication networks and paving the way for reliable and efficient vehicular communication systems.

Reconfigurable metasurface polarization rotator utilizing a phase-shifter-loaded truncated patch

This paper introduces a reconfigurable metasurface polarization rotator based on the linear to circular polarization decomposition concept. The design employs a simple truncated square patch configuration to accomplish linear-to-circular polarization decomposition. Following this, a phase shifter introduces an extra phase shift to one of the circularly polarized waves. This additional phase can be modified dynamically via external digital control. Subsequently, the waves are recombined into a new linearly polarized wave with a rotated orientation, which is reflected back into free space. A metasurface with 9×9 elements is designed and fabricated, which achieves 2-bit real-time linear polarization rotation. The proposed design is theoretically analyzed, and its performance is verified through full-wave simulating and experimental results.

Comparative Test of Novel Fluorescent Optical Antennas for LED‐ and Laser‐Based Optical Wireless Communications

AbstractFluorescent Concentrators (FCs) are set to revolutionize Optical Wireless Communications (OWC), offering significant advantages over traditional receivers, such as large Field of View (FoV) and enhanced optical gain (OG). In this study, three different Optical Antennas are presented and evaluated as OWC receivers, exploiting FCs incorporating different fluorophores. The performances of DQ1 and Lumogen Red 305F (LR305), and a newly synthesized fluorophore (H2) are comparatively tested for solar energy harvesting, never proposed before for OWC. The devices are tested in high bit rate, laser‐based OWC configuration, and for indoor LED‐based Visible Light Communication (VLC) by presenting a realistic indoor VLC transmitter‐receiver (TX‐RX) system embedding high‐power white LEDs as transmitter. The results demonstrate that all the proposed OAs exhibit greater angular stability than traditional detectors, potentially offering greater resilience to misalignment and beam wandering effects, particularly relevant also in Free Space Optical (FSO) configurations. Furthermore, the intrinsic properties of H2 and LR305 make them particularly suited for white‐light VLC applications. Based on a thorough experimental characterization, the work is the first to propose and evaluate in detail the performance of various new OAs, depending on the specific application, highlighting the efficiency of such devices across various OWC fields.

Common-path ghost imaging through complex media with dual polarization

The performance of ghost imaging (GI) is severely compromised by dynamic and complex scattering media in free space. In this Letter, we design a common-path GI (CPGI) setup with dual polarization in complex environments. The s-light and p-light with mutually perpendicular polarization states are generated and overlap in free space in the designed optical path to correct a series of dynamic scaling factors induced by the complex scattering media. Experimental results demonstrate that the proposed method is highly robust and can achieve high imaging quality in complex media. Compared to previous schemes, the proposed method adopts a simplified optical setup and realizes high-quality GI in complex and dynamic scattering environments without extra algorithms in order to promote the wider application of GI.

Predicting atmospheric turbulence for secure quantum communications in free space

Predicting atmospheric turbulence for secure quantum communications in free space

Coupling and propagation of strong-field THz waves on tungsten wires

Free-space strong-field terahertz (THz) radiation has significant applications in non-equilibrium quantum matter modulation, all-optical electron acceleration and manipulation, THz biomedical effects, and so on. However, certain applications like THz endoscopes, strong-field THz near-field nonlinear optics, and THz high-power devices require a deep understanding of strong-field THz–matter interaction mechanisms. Therefore, improving the manipulation of strong-field THz coupling and propagation characteristics, particularly through the use of metal wire waveguides, is crucial. To this end, we systematically investigate the coupling and propagation characteristics of strong-field THz waves on the surface of tungsten wires and implement two effective coupling methods: two-wire coupling and crossover coupling. This allows for a propagation distance of up to 100 mm along the tungsten surface as THz surface waves. This effective control of strong-field THz waves using metal wires enables the guidance of THz waves from free space into transmission lines and waveguides, which holds significant value for various specific applications.

Determining oscillator strengths of cesium from magic wavelengths of the D1 line

Abstract A magic-wavelength optical dipole trap (ODT) can eliminate the differential light shift of the transition between atomic states, so that transition frequency between the two states is the same as that in free space, which is of great significance for exploring atomic structure. Here we calculate the dynamic polarizabilities of the 6S1/2 ground state and 6P1/2 excited state of the cesium atom which are connected by the D1 line, by using the relativistic coupled cluster method, and obtain magic wavelengths of ODT laser for trapping the two states simultaneously. By using these magic wavelengths, we calculate oscillator strength of the 6P1/2 → 7D3/2 transition for linearly and circularly polarized lights. Furthermore, we analyze the influence of magic wavelengths on oscillator strengths.

Editorial

Welcome to the inaugural volume of Comm&Optics Connect, a multidisciplinary journal dedicated to advancing communication and networks across the entire electromagnetic spectrum. This first volume embodies our vision to provide a platform where groundbreaking research in radio, mmWave, THz, and optical technologies converges. The future of communication networks lies in the seamless integration of technologies across the electromagnetic spectrum to support ultra-high speed, ultra-low latency, and massive connectivity. However, realizing this vision requires overcoming significant challenges, such as managing the complexity of heterogeneous networks, ensuring robust security and privacy, and developing energy-efficient solutions. Comm&Optics Connect addresses these challenges by offering a platform for radio, mmWave, THz, and optical fields to share their work and collaboratively tackle these issues. The response to our call for papers reflects a strong interest in contributing to the aims and scope of the journal. The five articles featured in this volume represent the breadth and depth of research that Comm&Optics Connect aims to showcase. These articles cover critical areas such as: • Real-Time Cloud-based IoT for Energy Consumption Monitoring: Damien Campbell et al. present a cloud-based IoT platform for monitoring household electricity consumption, providing valuable insights into usage patterns and identifying opportunities for enhancing energy efficiency. This research exemplifies the journal’s focus on practical deployments. • Free Space Optical Inter-Satellite Links: Shivam Bhutiani and Nupur Shah explore the establishment of free space optical inter-satellite links beyond the Karman line. This work highlights the journal’s interest in cutting-edge communication technologies for space applications, aligning with the increasing demand for high-speed and reliable connectivity in satellite networks. • Enhancing Physical Layer Security: Shen Qian and Meng Cheng delve into physical layer security in lossy untrusted relay networks, focusing on the challenges and opportunities presented by finite blocklength transmissions. This research contributes to the journal’s commitment to exploring security and resilience in communication systems, an area of paramount importance as networks become more complex and vulnerable. • Open Fronthaul Technologies for 5G and Beyond: Hamna Shoukat et al. provide a comprehensive overview of technological trends in open fronthauls for beyond 5G and 6G networks. This work highlights the journal's emphasis on next-generation networks and the critical role of open and interoperable architectures in fostering innovation and flexibility. • Multi-Task Learning for Low-Complexity VLC Systems: Saksham Dewan and Hany Elgala explore the application of multi-task learning to reduce the complexity of visible light communication (VLC) systems. This research exemplifies the journal’s dedication to exploring novel data-driven approaches using deep learning (DL) models for enhanced efficiency and performance. As the Editor-in-Chief of Comm&Optics Connect, I am confident that the journal will become an essential resource for researchers in the field of communications and networks. None of this would be possible without the outstanding and diverse members of the editorial board, the hard-working staff at Scifiniti, and the valuable reviewers. I invite you to join us on this exciting journey as we bridge the gap between cutting-edge research and practical applications, shaping the future of a connected world. We look forward to receiving contributions from all over the world.

Enhancing Free Space Optical System Performance through Fog and Atmospheric Turbulence using Power Optimization

Free Space Optical (FSO) communication is gaining traction as a pivotal technology for next-generation communication systems, offering extremely high data rates, unlicensed bandwidth, and rapid transmission capabilities. However, its performance is significantly hindered by atmospheric factors such as turbulence and fog. This paper presents a comprehensive model for FSO communication designed to optimize performance under various atmospheric conditions. We assess channel capacity across a spectrum of weak to strong atmospheric turbulence using a Gamma-Gamma channel distribution. To mitigate channel losses, our system employs Wavelength Division Multiplexing (WDM) and multi-beam Multiple Input Multiple Output (MIMO) technologies. Results indicate that the integration of diversity techniques and WDM substantially enhances system performance in adverse weather conditions. Furthermore, power optimization is achieved through the implementation of optical amplifiers and feedback mechanisms from the receiver to the transmitter to adjust the transmitter power in accordance with received Bit Error Rate (BER). The proposed power-optimized WDM MIMO system demonstrates a remarkable BER of 1.48884e-15, while extending the transmission link distance to 2500 meters with a Q factor of 21.5 even under strong atmospheric turbulence conditions.

Escaping dynamics of inner gas from a bursting bubble in free space

Escaping dynamics of inner gas from a bursting bubble in free space

Multilayer homogenization and experimental demonstration of artificial plasma matched with free space

Multilayer homogenization and experimental demonstration of artificial plasma matched with free space

Pyramidal microwave absorbers: leveraging ceramic materials for improved electromagnetic interference shielding

This study presents the development and optimization of pyramidal microwave absorbers designed for efficient electromagnetic interference (EMI) reduction in anechoic chambers. Based on prior research, this work transitions from conventional flat cement-carbon absorbers to a novel pyramidal design, incorporating silicon carbide (SiC) as ceramic materials. Introducing ceramic materials into the cement-carbon composite aims to enhance absorption across a broader frequency range while maintaining structural integrity. The study evaluates five sets of pyramidal absorbers with varying SiC content within the 1–12 GHz frequency range. Reflectivity performance was assessed using the naval research laboratory (NRL) Arch free space method at a 0° incidence angle. Among the tested absorbers, the set containing 10% SiC demonstrated superior performance, achieving minimum and maximum reflectivity values of -26.6215 and -55.2752 dB, respectively, particularly in the C-band. The findings highlight the significant impact of material composition and porosity on the absorber's effectiveness, providing valuable insights for the future design of high-performance EMI absorbers.

LDPC-coded OAM shift-keying FSO communication system with dual-pattern CNN demodulator

An LDPC-coded orbital angular momentum shift-keying (OAM-SK) free space optical (FSO) communication system with a dual-pattern convolutional neural network (CNN) demodulator is put forward to resist the adverse effect of atmospheric turbulence (AT). Diverging from the standard single-pattern CNN demodulator, the proposed method inputs a dual OAM light pattern into the demodulator. The first pattern stems from the Laguerre-Gaussian OAM-SK light focused by a convex lens, while the second is acquired post-cylindrical lens modulation. The dual-pattern CNN demodulator can extract richer features from the incoming light, enhancing the recognition accuracy for OAM-SK modes. This advancement notably enables the recognition of OAM-SK modes with opposite orbital quantum numbers, a challenging task for standard single-pattern CNN demodulators. We have refined communication reliability by integrating LDPC coding with OAM-SK, and LDPC decoding has also been explicitly designed for OAM-SK channels. Simulations validate our proposed method, achieving a recognition accuracy 0.869 under strong AT (Cn2=5×10−14m−2/3). We use the image transmission as a benchmark; the dual-pattern CNN demodulator enhances the LDPC-coded OAM-SK FSO link, achieving a 30 dB boost in the image’s PSNR compared to the traditional CNN demodulation. The bit error rate (BER) drops to 3.8e−5, achieving significant advancement in comparison to the single-pattern CNN demodulators.

Influences and variations of wave impedance of electromagnetic fields generated by lightning return strokes

The domains of lightning electromagnetic pulse (LEMP) fields are classified as “near-field,” “intermediate-field,” and “far-field” based on qualitative descriptions. However, the systematic quantitative classification of LEMP fields is yet to be reported. This study characterized the wave impedance of lightning electromagnetic pulse (WILEMP) to solve this problem. The components and field domain distribution ranges of LEMP were analyzed by varying the WILEMP and the distance between the observation point and radiation source (r). The changes in the WILEMP with r under the influence of different factors were calculated using the finite-difference time-domain (FDTD) method. The results indicated that the LEMP field has high impedance. the WILEMP decreased rapidly with the increase in r when r ≤ 10 km, consistent with the characteristics of the electrostatic and induction fields (near field). The WILEMP gradually decreased and stabilized with the increase in r when r ≥ 20 km, and the value was roughly the same as the impedance of free space (377 Ω) when r = 100 km, consistent with the characteristics of radiation field (far field). The decay rate of the WILEMP was lower than that when r ≤ 10 km but higher than that when r ≥ 20 km. Finally, when 10 km < r < 20 km, the apparent transitivity was consistent with intermediate-field characteristics.

Half-time range description for the free space wave operator and the spherical means transform

Half-time range description for the free space wave operator and the spherical means transform

Free Volume Space of Polymers as a New Functional Nanospace: Synthesis of Guest Polymers.

Nanospace has been used as a specific field for syntheses and assemblies of molecules, polymers, and materials. Free volume space among polymer chains is related to their properties, such as permeation of gas and small molecules. However, the void has not been used as a functional nanospace in previous works. The present work shows synthesis of guest conductive polymers in free volume space of conventional synthetic resins and rubbers as a new nanospace. Vapor of heteroaromatic monomer and oxidative agent is diffused into the soft dynamic nanospace among the polymer chains under ambient pressure at low temperature. The oxidative polymerization provides the conductive polymers, such as polypyrrole (PPy), in the free volume space of poly(methyl methacrylate) (PMMA), polypropylene (PP), silicone rubber (SR), and polyurethane rubber (PU). The ratio of the free volume decreases with the infiltration of the conductive polymers. The composites exhibit the improved mechanical and gas barrier properties. The rubbers containing PPy are used as mechanical-stress sensors with both the conductivity and flexibility. The free volume space of resins and rubbers can be used as a new dynamic nanospace for synthesis of functional polymer composites.

240 Gbps SI-FMF/FSO communication system based on LP modes and PV code with the impact of foggy weather in Alexandria and Setif

This paper presents a novel, to the best of our knowledge, high-speed optical communication system achieving a 240 Gbps transmission capacity by integrating step-index few-mode fiber (SI-MMF) and free space optics (FSO). Knowing that Hermite-Gaussian modes (HGMs) are eigenmodes of a free space medium and the linearly polarized modes (LPMs) are eigenmodes of step-index few-mode fiber (SI-FMF), and by considering the similarity between HGM ( and ) and LPM ( and ), respectively, the system employs dual-polarization (DP) and linearly polarized (LP) modes (, , and ), combined with optical code division multiple access (OCDMA) using permutation vector (PV) codes. Each polarization state carries data from three LP modes, with each mode supporting four OCDMA channels, each assigned a unique PV code. The system’s performance is evaluated under varying fog conditions using key metrics such as quality-factor (Q-factor), bit error rate (BER), and eye diagrams, which provide a comprehensive assessment of signal strength and quality. Real-world applicability is assessed using meteorological data from two African cities, Alexandria, Egypt, and Setif, Algeria. System performance is characterized using the Q-factor, bit error rate (BER), and eye diagrams. The results show that, in Alexandria, successful transmission is achieved over 1.41 km. In Setif, the transmission distance is reduced to 1.31 km due to slightly higher atmospheric attenuation. These ranges are observed at a BER below HG00 and a Q-factor exceeding 3.10. Consequently, these findings confirm the viability of the proposed system for high-capacity optical communication in challenging weather conditions, making it suitable for future 6G networks.

A physical optics formulation of Bloch waves and its application to 4D STEM, 3D ED and inelastic scattering simulations.

Bloch waves are often used in dynamical diffraction calculations, such as simulating electron diffraction intensities for crystal structure refinement. However, this approach relies on matrix diagonalization and is therefore computationally expensive for large unit cell crystals. Here Bloch wave theory is re-formulated using the physical optics concepts underpinning the multislice method. In particular, the multislice phase grating and propagator functions are expressed in matrix form using elements of the Bloch wave structure matrix. The specimen is divided into thin slices, and the evolution of the electron wavefunction through the specimen calculated using the Bloch phase grating and propagator matrices. By decoupling specimen scattering from free space propagation of the electron beam, many computationally demanding simulations, such as 4D STEM imaging modes, 3D ED precession and rotation electron diffraction, phonon and plasmon inelastic scattering, are considerably simplified. The computational cost scales as {\cal O}({N^2} ) per slice, compared with {\cal O}({N^3} ) for a standard Bloch wave calculation, where N is the number of diffracted beams. For perfect crystals the performance can at times be better than multislice, since only the important Bragg reflections in the otherwise sparse diffraction plane are calculated. The physical optics formulation of Bloch waves is therefore an important step towards more routine dynamical diffraction simulation of large data sets.

Economic consequences of the phenomenon of uberization on the example of the services of selected carriers in the transport industry

Uberization is a process, phenomenon, trend, and direction that emerged in the 21st century economy thanks to Uber Technologies, Inc., which was the first to introduce a mobile application that connects drivers and passengers. Although the name of the trend was not formalized by the Uber corporation, it appeared a few years later to describe certain dependencies that emerged in the economy and that gained importance not only in the field of transportation services, but also in the field of finance, in the labor market, or in relation to the real estate market. The purpose of the study was to determine the impact of the progressive phenomenon of uberization on the competitiveness of the transportation industry in the pre-pandemic period and in the post-pandemic period. The study assumed the hypothesis that carpooling services, which are one of the important models of uberization, implemented in Poland through the BlaBlaCar app, can be a significant competitor to transportation services provided through traditional forms and models of communication, i.e., train and bus connections. The results of the study showed that BlaBlaCar services are a cheaper alternative to other means of transportation, i.e., public transport (Polskie Koleje Państwowe, PKP Intercity) and bus connections, although not always. As a rule, their competitiveness is higher for those routes and trips where there are many drivers offering free space in the car. On the other hand, on the routes less frequently visited by BlaBlaCar drivers, fares with a BlaBlaCar driver are higher than rail and bus fares. The considerations of the article meet the objectives of the cognitive goal and the application goal and showed that uberization in the transport industry is a significant phenomenon that is still developing and, in the future, may threaten traditional forms of transport, i.e., rail and bus travel.