Data Transmission Capacity Research Articles

Generation of Orbital Angular Momentum Light by Patterning Azopolymer Thin Films

Orbital angular momentum (OAM) encoding is a promising technique to boost data transmission capacity in optical communications. Most recently, azobenzene films have gained attention as a versatile tool for creating and altering OAM-carrying beams. Unique features of azobenzene films make it possible to control molecular alignment through light-induced isomerization about the azo bond. This feature enables the fabrication of diffractive optical devices such as spiral phase plates and holograms by accurately imprinting a phase profile on the incident light. By forming azobenzene sheets into diffractive optical elements, such as spiral phase plates, one can selectively create OAM-carrying beams. Due to the helical wavefront and phase variation shown by these beams, multiple distinct channels can be encoded within a single optical beam. This can significantly increase the data transmission capacity of optical communication systems with this OAM multiplexing technique. Additionally, holographic optical components made from azobenzene films can be used to build and reconstruct intricate wavefronts. It is possible to create OAM-based holograms by imprinting holographic designs on azobenzene films, which makes it simpler to control and shape optical beams for specific communication requirements. In addition, azobenzene-based materials can then be suitable for integration into optical communication devices because of their reconfigurability, compactness, and infrastructure compatibility, which are the main future perspectives for achieving OAM-based technologies for the next generation, among other factors. In this paper, we see the possible use of azobenzene films in the generation and modification of OAM beams for optical communications through light-induced isomerization. In addition, the potential role of azobenzene films in the development of novel OAM-based devices that paves the way for the realization of high-capacity, OAM-enabled optical communication networks are discussed.

Transmission of optical communication signals through ring core fiber using perfect vortex beams.

Orbital angular momentum can be used to implement high capacity data transmission systems that can be applied for classical and quantum communications. Here we experimentally study the generation and transmission properties of the so-called perfect vortex beams and the Laguerre-Gaussian beams in ring-core optical fibers. Our results show that when using a single preparation stage, the perfect vortex beams present less ring-radius variation that allows coupling of higher optical power into a ring core fiber. These results lead to lower power requirements to establish fiber-based communications links using orbital angular momentum and set the stage for future implementations of high-dimensional quantum communication over space division multiplexing fibers.

Last mile access-based FSO and VLC systems

Free-space optics (FSO) and visible light communication (VLC) are interesting solutions for last mile access due to their benefits over conventional wired and wireless communication systems, including easy installation, low latency, high bandwidth, and low cost. This study aims to present last mile access using hybrid FSO/VLC, addressing the shortcomings of each technology. A hybrid system might, for instance, use VLC to give last meter connectivity to specific buildings and FSO to provide high-bandwidth outdoor connectivity across vast distances. In this paper, three proposed scenarios are designed using Optisystem and Matlab software, employing pulse amplitude modulation with four levels (PAM-4). The first scenario involves designing the last mile of the FSO-VLC system. In contrast, the second uses wavelength division multiplexing (WDM) technology to increase the data transmission capacity by enabling multiple optical signals at various wavelengths. The last scenario entails using VLC systems and the non-orthogonal multiple access (NOMA) approach to accommodate several users simultaneously. The simulation results show that the proposed system can fulfill outdoor link distances of more than 10 km and indoor coverage of about 2 m with a bit-error rate (BER) of 1.5×10−32 for a 10 Gbps data rate. However, the proposed systems can achieve the same data rate with a reduced FSO distance under different turbulence and weather conditions.

Layered Gallium Monosulfide as Phase‐Change Material for Reconfigurable Nanophotonic Components On‐Chip

AbstractThe demand for information processing at ultrahigh speed with large data transmission capacity is continuously rising. Necessary building blocks for on‐chip photonic integrated circuits (PICs) are reconfigurable integrated low‐loss high‐speed modulators and switches. Phase change materials (PCMs) provide unique opportunities for integration into PICs. Here, the investigation of layered gallium monosulfide (GaS) as a novel low‐loss PCM from infrared to optical frequencies is pioneered, with high index contrast (Δn ≈0.5) at the optical telecommunication band. The GaS bandgap switches from 1.5 ± 0.2 eV for the amorphous state to 2.1 ± 0.1 eV for the crystalline state. It is demonstrated that the reversible GaS amorphous‐to‐crystalline phase transition can be operated thermally and by picosecond green (532 nm) laser irradiation. The design of a reconfigurable integrated optical modulator on‐chip based on Mach‐Zehnder Interferometers (MZI) with the GaS PCM cell deposited on one of the arms for application is presented at the telecommunication wavelength of λ = 1310 nm, where the standard single mode optical fiber exhibits zero chromatic dispersion, and at λ = 1550 nm, where a minimum optical loss of 0.22 dB km−1 is obtained. This opens the route to applications such as reconfigurable modulators, beam steering using phase modulation, and photonic neural networks.

Stroke telemedicine: yesterday, today and tomorrow

Introduction. Telemedicine, by fitting into the long chain of events of the patient’s fate, plays an integrative role, allowing all stages of stroke care to be monitored.The aim of the study was to analyse and systematise the scientific literature in the context of the development of telemedicine for stroke.Materials and methods. Narrative review is compiled from literature sources found in the scientific electronic library eLIBRARY.RU and the National Library of Medicine database (PubMed.gov) using the keywords “telemedicine”, “stroke”, “telestroke” for the years 1999 to 2022.Results and discussion. The emergence of thrombolytic therapy perceived as a risk treatment, the lack of specialists to provide round-the-clock care, the requirement of regulatory authorities to improve the quality of care and technological improvements in data transmission capacity served to develop stroke telemedicine in the first decade of the 21st century. In the second decade of the 21st century telestroke, which initially originated in North America and Western Europe, began to spread widely around the world. The pandemic of a new coronavirus infection at the turn of the third decade of the 21st century provided the greatest impetus for the development of telemedicine in general and was the third impetus for the development of stroke telemedicine. Stroke telemedicine is pushing the boundaries of clinical practice, making specialised care more accessible and less dependent on local manpower.Conclusion. Further evolution of telemedicine for stroke will proceed in three directions: (1) telemedicine for stroke will become routine clinical practice; (2) telemedicine for stroke will become more personalized; and (3) regional telestroke networks will be connected to national and international telestroke networks, and stroke telemedicine networks will develop.

Trench-assisted multi-ring-core fiber for orbital angular momentum modes

Orbital angular momentum (OAM) multiplexing technology has attracted significant interest due to its ability to increase the data transmission capacity in optical communications. By combining OAM-based mode division multiplexing (MDM) and wavelength division multiplexing (WDM) techniques in multi-core fiber (MCF), the transmission rate and spectral efficiency of the optical communication systems can be greatly enhanced. In this paper, we present a design of a multi-ring air-core trench-assisted fiber that supports transmission over the entire C + L (1530–1625 nm) band with low inter-ring crosstalk. The high-contrast ring and trench design can effectively suppress the inter-modal crosstalk. The effects of the ring spacing, wavelength range and doping concentration on the crosstalk suppression are also systematically investigated. Furthermore, the complexity of the MIMO processing system is greatly reduced with a fewer-optical-core structure while keeping low inter-ring crosstalk. The results demonstrate that our designed fiber can support 140 OAM modes at 1550 nm with < −79.4 dB inter-ring crosstalk at low Ge-doped concentration (12.5 mol%), and it can keep the inter-ring crosstalk below −66.56 dB across the C + L band, which features lower inter-ring crosstalk than the other reports while supporting more OAM modes. Furthermore, to support more OAM modes with lower inter-ring crosstalk and intra-modal crosstalk, we further provide a second low-doping-concentration (12.5 mol%) fiber design, which can support 196 OAM modes with < −35.74 dB inter-ring crosstalk and Δneff > 5.39 × 10−4. Additionally, our designed fiber can support 224 OAM modes (37.5 mol% Ge-doped) and < −63 dB inter-ring crosstalk with low intra-modal crosstalk (Δneff > 5.45 × 10−4) and flat dispersion distribution (chromatic dispersion slope lower than 0.171 ps/nm2/km) across the C + L band.

Spatial and Polarization Division Multiplexing Harnessing On‐Chip Optical Beam Forming

AbstractOn‐chip spatial and polarization multiplexing has emerged as a powerful strategy to boost the data transmission capacity of integrated optical transceivers. State‐of‐the‐art multiplexers require accurate control of the relative phase or the spatial distribution among different guided optical modes, seriously compromising the optical transmission bandwidth and performance of the devices. To overcome this limitation, a new approach based on the coupling between guided modes in integrated waveguides and optical beams free‐propagating on the chip plane is proposed. The engineering of the evanescent coupling between the guided modes and free‐propagating beams allows spatial and polarization multiplexing with state‐of‐the‐art performance. A two‐polarization multiplexed link and a three‐mode multiplexed link using standard 220‐nm‐thick silicon‐on‐insulator technology have been developed. The two‐polarization link shows a measured −35 dB crosstalk bandwidth of 180 nm, while the three‐mode link exhibits a −20 dB crosstalk bandwidth of 195 nm. These links are used to demonstrate error‐free operation (bit‐error‐rate &lt;10−9) in multiplexing and demultiplexing of two and three non‐return‐to‐zero signals at 40 Gbps each, with power penalties below 0.08 and 1.5 dB for the two‐polarization and three‐mode links, respectively. The approach demonstrated for two polarizations and three modes is transferable to future implementation of more complex multiplexing schemes.

High-Speed Carbon Nanotube Photodetectors for 2 μm Communications.

In the era of big data, the growing demand for data transmission capacity requires the communication band to expand from the traditional optical communication windows (∼1.3-1.6 μm) to the 2 μm band (1.8-2.1 μm). However, the largest bandwidth (∼30 GHz) of the current high-speed photodetectors for the 2 μm window is considerably less than the developed 1.55 μm band photodetectors based on III-V materials or germanium (>100 GHz). Here, we demonstrate a high-performance carbon nanotube (CNT) photodetector that can operate in both the 2 and 1.55 μm wavelength bands based on high-density CNT arrays on a quartz substrate. The CNT photodetector exhibits a high responsivity of 0.62 A/W and a large 3 dB bandwidth of 40 GHz (setup-limited) at 2 μm. The bandwidth is larger than that of existing photodetectors working in this wavelength range. Moreover, the CNT photodetector operating at 1.55 μm exhibits a setup-limited 3 dB bandwidth over 67 GHz at zero bias. Our work indicates that CNT photodetectors with high performance and low cost have great potential for future high-speed optical communication at both the 2 and 1.55 μm bands.

Simple polarization-insensitive coherent RoF link with increased capacity.

A simple polarization-insensitive coherent radio-over-fiber (RoF) link with increased spectrum efficiency and transmission capacity is proposed and demonstrated. Instead of using two polarization splitters (PBSs), two 90° hybrids, and four pairs of balanced photodetectors (PDs) in a conventional polarization-diversity coherent receiver (PDCR), a simplified PDCR with only one PBS, one optical coupler (OC), and two PDs is employed in the coherent RoF link. At the simplified receiver, a novel, to the best of our knowledge, digital signal processing (DSP) algorithm is proposed to achieve polarization-insensitive detection and demultiplexing of two spectrally overlapping microwave vector signals as well as the elimination of the joint phase noise originating from the transmitter and the local oscillator (LO) laser sources. An experiment is performed. The transmission and detection of two independent 16QAM microwave vector signals at identical microwave carrier frequencies of 3 GHz with a symbol rate of 0.5 GSym/s over a 25-km single-mode fiber (SMF) is demonstrated. Thanks to the spectrum superposition of the two microwave vector signals, the spectral efficiency as well as the data transmission capacity is increased.

Detailed performance investigation and BER characterization of S+C+L band-WDM transmission system

Recently, ultra-wideband (UWB) wavelength-division multiplexing (WDM) technique has been introduced to increase the data transmission capacity of optical system using the same infrastructure fibers. This capacity increase will raise the effect of fiber nonlinearity and stimulated Raman scattering (SRS) due to the increase of total launch power and operating wavelength band, respectively. This paper presents comprehensive investigation of UWB spectral characteristics of the fiber nonlinear interference (NLI) in dual-polarization (DP)− 16QAM S+C+L system. The investigation is based on enhanced Gaussian noise (EGN) model and takes into account the wavelength dependence of various fiber parameters. The results are used as a guide line to assess the transmission performance of the system under different values of symbol rate Rs (50–80 GBaud). The results reveal that a maximum transmission reach of 13 100 km-spans is achieved for Rs= 50 GBaud and 75 GHz channel spacing.

NOMA-enabled Cooperative V2V Communications with Fixed-Gain AF Relaying

By virtue of its improving bandwidth efficiency along with user fairness, non-orthogonal multiple access (NOMA) technique is considered a promising method for next-generation wireless communication systems. Since fading effect of wireless channels in vehicle-to-vehicle (V2V) communication systems are more severe than those in traditional systems, in this study, we employ the power-domain downlink NOMA technique in cooperative V2V communication systems to enhance data transmission capacity and network efficiency. In the proposed system, the base station communicates with two vehicular nodes, namely near and far users, through a relay vehicle employing the fixed-gain amplify-and-forward scheme. In real-life scenarios, the relay and the users move in high velocities; hence, the corresponding fading channels between these nodes are exposed as having double-Rayleigh fading characteristic in which the fading coefficient of a wireless channel is modeled as the product of two Rayleigh distributed random variables. To analyze the system performance, we first investigate the outage probability and derive its exact closed-form expressions for the near and far users. Then, we make the exact ergodic capacity analysis and obtain the closed-form solution for the near user. Furthermore, outage and ergodic performances of the NOMA-enabled system are compared to the simulation results of the traditional orthogonal multiple access approach. We also give analytic and numerical results to evaluate the performance of the proposed system and show the consistency of Monte-Carlo simulations with analytical derivations. It is observed that even with the small power allocation, both performances of the near user mostly outperform the far user.

Heterogeneously Integrated Multicore Fibers for Smart Oilfield Applications

In the context of Industry 4.0, the smart oilfield is introduced, which relies on large-scale information exchange among various parts, and there is an urgent need for special fiber links for both increased data transmission capacity and high-sensitivity distributed sensing. Multicore fibers can be expected to play a critical role, in the parts of cores that are responsible for data transmission, while others are used for sensing. In this paper, we propose a heterogeneously integrated seven-core fiber for interconnection and awareness applications in smart oilfields, which could not only support digital and analog signal transmission but could also measure temperature and vibration. The core for digital signal transmission has a low differential mode group delay of 10 ps/km over the C-band, and the crosstalk between adjacent cores is lower than −55 dB/km at the pitch of 50 μm. A 25-Gbaud transmission over 50 km is simulated. Each core for analog signal transmission has a large effective area of 172 μm2 to suppress the nonlinear effect due to the watt-scale input power. The proposed heterogeneously multicore fiber exhibits great potential to be applied in smart oilfields, meeting the demand for efficient and cost-effective oil production.

Multiway Relay Based Framework for Network Coding in Multi-Hop WSNs

In today’s information technology (IT) world, the multi-hop wireless sensor networks (MHWSNs) are considered the building block for the Internet of Things (IoT) enabled communication systems for controlling everyday tasks of organizations and industry to provide quality of service (QoS) in a stipulated time slot to end-user over the Internet. Smart city (SC) is an example of one such application which can automate a group of civil services like automatic control of traffic lights, weather prediction, surveillance, etc., in our daily life. These IoT-based networks with multi-hop communication and multiple sink nodes provide efficient communication in terms of performance parameters such as throughput, energy efficiency, and end-to-end delay, wherein low latency is considered a challenging issue in next-generation networks (NGN). This paper introduces a single and parallels stable server queuing model with a multi-class of packets and native and coded packet flow to illustrate the simple chain topology and complex multiway relay (MWR) node with specific neighbor topology. Further, for improving data transmission capacity in MHWSNs, an analytical framework for packet transmission using network coding at the MWR node in the network layer with opportunistic listening is performed by considering bi-directional network flow at the MWR node. Finally, the accuracy of the proposed multi-server multi-class queuing model is evaluated with and without network coding at the network layer by transmitting data packets. The results of the proposed analytical framework are validated and proved effective by comparing these analytical results to simulation results.

Security During Transmission Of Data Using Web Steganography

The enormous improvements in communications and related technologies, such as the Internet of Things (IoT) and its web-based and mobile applications, have changed our way of life. We are also noticing a trend in which internet-connected electronic devices are using technology more frequently and providing customers with services of a higher standard. However, there are several complications and issues that arise when sending and receiving information via the internet. The security, privacy, and preservation of sent information are the most critical of them all. The security of information has grown to be a significant problem with the expansion of data transfer across computer networks. There are numerous ways to safeguard data and prevent unwanted users from accessing it. Steganography and cryptography are two different data hiding and protection techniques. Steganography conceals communications within some other digital media. On the other side, cryptography obscures the message's content and makes it challenging for readers to decipher. To safeguard data, steganography can be combined with cryptographic methods. Combining steganography and cryptography for hidden data transmission is the best suggested method for protecting data transferred over the internet. A data carrier that is an image can be used for the transmission. With regard to capacity, security, and robustness for secure data transmission over an open channel, this combinational methodology will be sufficient. The purpose of this paper is to explain the steganographic security measures used to protect data while it is being transmitted across a network. Key words: Security, Transmission, Data, Web Steganography

A Practical Cross-Device Federated Learning Framework over 5G Networks

The concept of federated learning (FL) was first proposed by Google in 2016. Since then, FL has been widely studied for the feasibility of application in various fields due to its potential to make full use of data without compromising privacy. However, limited by the capacity of wireless data transmission, the employment of FL on mobile devices has been making slow progress in practice. The development and commercialization of the 5th generation (5G) mobile networks has shed some light on this. In this article, we analyze the challenges of existing FL schemes for mobile devices and propose a novel cross-device FL framework that utilizes the anonymous communication technology and ring signature to protect the privacy of participants while reducing the computation overhead of mobile devices participating in FL. In addition, our scheme implements a contribution-based incentive mechanism to encourage mobile users to participate in FL. We also give a case study of autonomous driving. Finally, we present the performance evaluation of the proposed scheme and discuss some open issues in FL.

Research and Simulation of OCDM Switch Layer Based on 2D WDM-Optical Code Switching Structure

Optical Communication is widely used in military and civilian backbone network communication, but due to the limitation of “electronic bottleneck”, the ability of network nodes to process information and optical layer data transmission capacity is seriously mismatched, which directly causes optical cross connectors in optical nodes. The number of ports carried has skyrocketed. In order to improve the processing speed of network nodes, this paper studies the four-layer multi-granularity switching system of optical fiber, wavelength band, wavelength, and optical code, and finally builds a complete OCDMA system through simulation software, simulates multi-user simulation, and successfully realizes The encoding and decoding process is analyzed, and the performance simulation and analysis of the core switching module of the four-layer multi-layer optical switching system-OCDM switching module are carried out, and the feasibility and superiority of the selected system are verified.

Tracking Efficiency Improvement According to Incident Beam Size in QPD-Based PAT System for Common Path-Based Full-Duplex FSO Terminals.

Free space optical (FSO) communication can support various unmanned aerial vehicles’ (UAVs) applications that require large capacity data transmission. In order to perform FSO communication between two terminals, it is essential to employ a pointing, acquisition, and tracking (PAT) system with an efficient and optimal performance. We report on the development of a common optical-path-based FSO communication system, tailored for applications in UAVs. The proposed system is equipped with a quadrant photodiode (QPD)-based PAT system without an additional beacon beam subsystem. The presented approach reduced the structural complexity and improved the tracking efficiency for the same size, weight, and power (SWaP). To achieve a robust FSO link in a dynamic UAV environment, the observability and controllability were obtained based on the linearized control according to the incident beam size on the QPD, which was verified by optical simulation and experiments. As a result, the QPD-based PAT system for implementing FSO links demonstrated an up to 4.25 times faster tracking performance. Moreover, the FSO link experimentally confirmed the 1.25 Gbps full-duplex error-free communication at a 50 m distance.

Optical Polarization Division Multiplexing Transmission System Based on Simplified Twin-SSB Modulation.

Optical twin-single sideband (Twin-SSB) modulation, due to the left sideband (LSB) and right sideband (RSB) signal carrying individual data, has become an attractive technique in fiber transmission because it satisfies the demand of the explosive increase in data traffic. This paper focuses on reducing the complexity of Twin-SSB system and further enhancing the spectral efficiency by proposing a polarization division multiplexing (PDM) Twin-SSB modulation scheme. LSB and RSB signals are extracted using de-mapping algorithm instead of optical bandpass filters (OBPFs) to reduce system complexity. To further improve spectral efficiency, PDM is employed to meet the polarization multiplexing transmission and achieve a higher transmission capacity. Based on the PDM Twin-SSB system, the LSB is 3-arr phase-shift-keying (3PSK) modulated, while RSB is quadrature phase-shift keying (QPSK) modulated. We simulated that the bit error ratio (BER) performance of LSB and RSB of X-polarization (X-Pol) and Y-polarization (Y-Pol) at 8-Gbaud, 10-Gbaud, 12-Gbaud, 14-Gbaud, and 16-Gbaud in the case of back-to-back (BTB) and 2 km standard single-mode fiber (SSMF) transmission. The simulation results verify the effectiveness and practical feasibility of the proposed PDM Twin-SSB scheme for future short-distance transmission owing to low cost, simplified structure, low algorithm complexity, and high data transmission capacity.

Ultralow Noise and Timing Jitter Semiconductor Quantum-Dot Passively Mode-Locked Laser for Terabit/s Optical Networks

Diode optical frequency comb lasers are promising compact solutions to generate high-speed optical pulses for applications in high spectral efficiency wavelength division multiplexing transmission with advanced modulation formats. In this paper, an InAs/InP quantum dot (QDot) C-band single-section passively mode-locked laser (MLL) based broadband optical frequency comb source with a free spectral range of 28.4 GHz is presented. The device exhibits less than 1.5 MHz optical linewidth (phase noise) over 56 channels and 2.1 fs pulse-to-pulse timing jitter with a central wavelength of 1550 nm. Using this comb, we demonstrate an aggregate data transmission capacity of 12.5 Terabit/s over 100 km of standard single mode fiber by employing dual-polarization with 16 QAM modulation format. This investigation shows the viability for semiconductor QDot MLLs to be used as low-cost optical source in Terabit/s or higher optical networks.

Efficient mode converters and filters using asymmetrical directional couplers with subwavelength gratings.

Mode-division multiplexing (MDM) is a promising solution to improve data transmission capacity for future optical interconnect networks. Mode converters and mode filters play a key role in on-chip MDM systems. Here, we propose and experimentally demonstrate a device, enabling mode conversion and filtering simultaneously, which is composed of asymmetrical directional couplers with subwavelength gratings, in a small footprint of 14.7 µm × 1.42 µm. The device can realize optical mode conversion between the first-order transverse electric (TE) mode and the fundamental TE mode, and can also filter the fundamental TE mode efficiently. The conversion efficiency is over 95%, with a broad 1 dB bandwidth over 80 nm and a high mode extinction ratio of >29 dB. As a mode filter, strong mode elimination of >30 dB is achieved.