Search Results (113)

Visible light communication (VLC) is an emerging optical wireless technology capable of delivering high data rates for both indoor and outdoor environments. When combined with multiple-input, multiple-output (MIMO) systems, VLC demonstrates enhanced capacity, extended transmission range, and improved reliability. However, VLC systems are susceptible to ambient light interference, which can degrade performance. This paper investigates the performance of MIMO-VLC systems using three modulation techniques: non-return to zero (NRZ), return to zero (RZ), and quadrature phase shift keying (QPSK). The study evaluates the VLC systems in terms of bit error rate (BER), quality factor (Q-factor), and received power over varying link distances. The obtained results show that MIMO-based systems outperform single-input, single-output (SISO) systems in terms of transmission range, with MIMO achieving up to 1450 m using QPSK, compared to 1125 m for SISO. Under ambient light noise, MIMO-based systems experience a greater reduction in transmission distance (13.6%) compared to SISO (6.2%), but the overall performance gain of MIMO compensates for this degradation. Among the modulation schemes, NRZ and QPSK provide the best performance, showing greater resilience to ambient light interference. The findings confirm that MIMO–VLC systems, particularly with NRZ and QPSK, offer a robust solution for overcoming interference and maximizing transmission distance in real-world applications. Full article

High demand for 6G wireless has made photonics-aided D-band (110–170 GHz) communication a research priority. Photonics-aided technology integrates optical and wireless communications to boost spectral efficiency and transmission distance. This study presents a Radio-over-Fiber (RoF) communication system utilizing photonics-aided technology for 4600 m long-distance D-band transmission. We successfully show the transmission of a 50 Gbps (25 Gbaud) QPSK signal utilizing a 128.75 GHz carrier frequency. Notwithstanding these encouraging outcomes, RoF systems encounter considerable obstacles, including pronounced nonlinear distortions and phase noise related to laser linewidth. Numerous factors can induce nonlinear impairments, including high-power amplifiers (PAs) in wireless channels, the operational mechanisms of optoelectronic devices (such as electrical amplifiers, modulators, and photodiodes), and elevated optical power levels during fiber transmission. Phase noise (PN) is generated by laser linewidth. Despite the notable advantages of classical Volterra series and deep neural network (DNN) methods in alleviating nonlinear distortion, they display considerable performance limitations in adjusting for phase noise. To address these problems, we propose a novel post-processing approach utilizing a two-dimensional convolutional neural network (2D-CNN). This methodology allows for the extraction of intricate features from data preprocessed using traditional Digital Signal Processing (DSP) techniques, enabling concurrent compensation for phase noise and nonlinear distortions. The 4600 m long-distance D-band transmission experiment demonstrated that the proposed 2D-CNN post-processing method achieved a Bit Error Rate (BER) of 5.3 × 10⁻³ at 8 dBm optical power, satisfying the soft-decision forward error correction (SD-FEC) criterion of 1.56 × 10⁻² with a 15% overhead. The 2D-CNN outperformed Volterra series and deep neural network approaches in long-haul D-band RoF systems by compensating for phase noise and nonlinear distortions via spatiotemporal feature integration, hierarchical feature extraction, and nonlinear modelling. Full article

This work presents a high-speed hybrid communication system integrating Underwater Optical Wireless Communication (UOWC), Multimode Fiber (MMF), and Free-Space Optics (FSO) channels, leveraging Orbital Angular Momentum (OAM) beams for enhanced data transmission. A Photodetector, Remodulate, and Forward Relay (PRFR) is employed to enable wavelength conversion from 532 nm for UOWC to 1550 nm for MMF and FSO links. Four distinct OAM beams, each supporting a 5 Gbps data rate, are utilized to evaluate the system’s performance under two scenarios. The first scenario investigates the effects of absorption and scattering in five water types on underwater transmission range, while maintaining fixed MMF length and FSO link. The second scenario examines varying FSO propagation distances under different fog conditions, with a consistent underwater link length. Results demonstrate that water and atmospheric attenuation significantly impact transmission range and received optical power. The proposed hybrid system ensures reliable data transmission with a maximum overall transmission distance of 1125 m (comprising a 25 m UOWC link in Pure Sea (PS) water, a 100 m MMF span, and a 1000 m FSO range in clear weather) in the first scenario. In the second scenario, under Light Fog (LF) conditions, the system achieves a longer reach of up to 2020 m (20 m UOWC link + 100 m MMF span + 1900 m FSO range), maintaining a BER ≤ 10⁻⁴ and a Q-factor around 4. This hybrid design is well suited for applications such as oceanographic research, offshore monitoring, and the Internet of Underwater Things (IoUT), enabling efficient data transfer between underwater nodes and surface stations. Full article

Due to its narrow divergence, optical wireless power transmission (OWPT) is promising for long-distance transmission systems. In OWPT systems, matching the beam shape with the solar cell geometry is crucial for both efficiency and safety. When the light is incident at an oblique angle, the beam is distorted in an axial direction, which requires appropriate beam shape control. In this study, a cylindrical lens system was designed to ensure uniform and effective light beam irradiation, even under oblique incidence conditions. A numerical model of the optical system was constructed, and it was experimentally confirmed that the beam shape could be controlled within 5% error over a transmission range of 1 m. The optical system was integrated with solar cell detection for consistent target recognition and beam irradiation, and its functionality was experimentally validated. The results are useful for expanding the application and infrastructure design in OWPT. Full article

Electric vehicles (EVs) are becoming more widespread as we move toward a carbon-free society. However, challenges remain, such as the need for large batteries, the inconvenience of charging, and limited driving range. Dynamic optical wireless power transmission (D-OWPT) is considered a promising solution to these problems. This paper investigates the infrastructure configuration and feasibility of D-OWPT. To this end, a model of EV power consumption was created, and a simulator for D-OWPT was developed. Using this simulator, it was shown that placing light sources in low-speed sections is an effective method, and that continuous driving can be achieved by providing a light source with an output of about 20 kW, assuming a 50% of light irradiation section ratio. Since many of the conditions used in the analysis are achievable with existing technologies, these results demonstrate the high feasibility of D-OWPT. While the analysis presented in this study is based on simulation, the modeling parameters, including EV power consumption and OWPT system characteristics, are derived from actual vehicle specifications and experimental data reported in OWPT research. Although this study does not include physical implementation, the results present numerically validated conditions that are directly applicable to practical system design. This work is intended to serve as a theoretical foundation for the future development and prototyping of D-OWPT infrastructure. Full article

In recent years, many studies have been conducted on OFDM-based optical wireless communications to develop a 6G communication infrastructure to improve data transmission and reduce the BER. Real-time optimal power management can enhance the data transmission speed and received power in an optical wireless channel under various conditions. This paper discusses implementing a real-time optimal power allocation system using a neural network for OFDM-based optical wireless communications. The system is designed to manage transmitter power, enhancing data transmission rates in optical wireless channels. In system design, data concerning power allocation for various types of OFDM-based optical wireless channels are calculated analytically, including the BER, SNR, fog effects, and fading types in the channel model. Next, a DNN neural model is trained using data generated from the analytical method. The trained model is finally integrated into wireless optical communication transmitter hardware. The experimental results indicate that the embedded power allocation system processes power allocation quickly. The proposed system achieves an average accuracy of 98% in power allocation, surpassing the analytical method. When used in wireless optical communication transmitters, this embedded system enhances speed and accuracy in power management, optimizing the data transmission rate up to 16 Gbps for a 500 m channel. Full article

In this paper, we present recent advancements in transmitter and receiver technologies for Optical Wireless Communication (OWC). OWC offers very wide license-free optical spectrum which enables very high capacity transmission. Additionally, beam-steered OWC is more power-efficient and more secure due to low divergence of light. One of the main challenges of OWC is wide angle transmission and reception because law of conservation of etendue restricts maximization of both aperture and field of view (FoV). On the transmitter side, we use Micro Electro-Mechanical System cantilevers activated by piezoelectric actuators together with silicon micro-lenses for narrow laser beam steering. Such design allowed us to experimentally demonstrate at least 10 Gbps transmission over 100° full angle FoV. On the receiver side, we show the use of photodiode array, and Indium-Phosphide Membrane on Silicon (IMOS) Photonic Integrated Circuit (PIC) with surface grating coupler (SGC) and array of SGC. We demonstrate FoV greater than 32° and 16 Gbps reception with photodiode array. PIC receiver allowed to receive 100 Gbps WDM with single SGC, and 10 Gbps with an array of SGC which had 8° FoV in the vertical angle and full FoV in the horizontal angle. Our results suggest that solutions presented here are scalable in throughputs and can be adopted for future indoor high-capacity OWC systems. Full article

In response to the urgent demands of the Internet of Things for precise indoor target positioning and information interaction, this paper proposes a multi-band analog radio-over-fiber mobile fronthaul system. The objective is to obtain the target’s location in indoor environments while integrating remote beamforming capabilities to achieve wireless access to the targets. Vector signals centered at 3, 4, 5, and 6 GHz for indoor positioning and centered at 30 GHz for wireless access are generated centrally in the distributed unit (DU) and fiber-distributed to the active antenna unit (AAU) in the multi-band analog radio-over-fiber mobile fronthaul system. Target positioning is achieved by radiating electromagnetic waves indoors through four omnidirectional antennas in conjunction with a pre-trained neural network, while high-speed wireless communication is realized through a phased array antenna (PAA) comprising four antenna elements. Remote beamforming for the PAA is implemented through the integration of an optical true time delay pool in the multi-band analog radio-over-fiber mobile fronthaul system. This integration decouples the weight control of beamforming from the AAU, enabling centralized control of beam direction at the DU and thereby reducing the complexity and cost of the AAU. Simulation results show that the average accuracy of localization classification can reach 86.92%, and six discrete beam directions are achieved via the optical true time delay pool. In the optical transmission layer, when the received optical power is 10 dBm, the error vector magnitudes (EVMs) of vector signals in all frequency bands remain below 3%. In the wireless transmission layer, two beam directions were selected for verification. Once the beam is aligned with the target device at maximum gain and the received signal is properly processed, the EVM of millimeter-wave vector signals remains below 11%. Full article

The rapid advancement of terahertz (THz) communication systems has positioned this technology as a key enabler for next-generation telecommunication networks, including 6G, secure communications, and hybrid wireless-optical systems. This review comprehensively analyzes THz communication, emphasizing its integration with free-space optical (FSO) systems to overcome conventional bandwidth limitations. While THz-FSO technology promises ultra-high data rates, it is significantly affected by atmospheric absorption, particularly absorption beyond 500 GHz, where the attenuation exceeds 100 dB/km, which severely limits its transmission range. However, the presence of a lower-loss transmission window at 680 GHz provides an opportunity for optimized THz-FSO communication. This paper explores recent developments in high-power THz sources, such as quantum cascade lasers, photonic mixers, and free-electron lasers, which facilitate the attainment of ultra-high data rates. Additionally, adaptive optics, machine learning-based beam alignment, and low-loss materials are examined as potential solutions to mitigating signal degradation due to atmospheric absorption. The integration of THz-FSO systems with optical and radio frequency (RF) technologies is assessed within the framework of software-defined networking (SDN) and multi-band adaptive communication, enhancing their reliability and range. Furthermore, this review discusses emerging applications such as self-driving systems in 6G networks, ultra-low latency communication, holographic telepresence, and inter-satellite links. Future research directions include the use of artificial intelligence for network optimization, creating energy-efficient system designs, and quantum encryption to obtain secure THz communications. Despite the severe constraints imposed by atmospheric attenuation, the technology’s power efficiency, and the materials that are used, THz-FSO technology is promising for the field of ultra-fast and secure next-generation networks. Addressing these limitations through hybrid optical-THz architectures, AI-driven adaptation, and advanced waveguides will be critical for the full realization of THz-FSO communication in modern telecommunication infrastructures. Full article

This study proposes optimizing the performance of free space optic signal transmission using spatial division multiplexing. The research uses different modified duobinary modulation schemes to model and optimize three hybrid mode division multiplexing-free-space optical (MDM-FSO) channels, each operating at 40 Gb/s–40 GHz. The study also includes the parametric optimization of various components to enhance system performance. The findings are significant for achieving high data rate links for backhaul solutions and improving bandwidth for future MDM-based wireless distributed networks. The research shows that employing three linearly polarized modes as data transmission channels with direct detection can be effective. Additionally, it is discovered that adjusting the bias voltages of the two LiNbO₃ modulators can improve power sharing between the modes, thereby mitigating the power penalty. Full article

Photonic millimeter-wave communication systems are promising for high-capacity, high-speed wireless networks, and their production is driven by the growing demand from data-intensive applications. However, challenges such as inter-symbol interferences (ISIs), inter-band interferences (IBIs), symbol timing offsets (STOs), and nonlinearity impairments exist, especially in non-orthogonal multiband configurations. This paper proposes and demonstrates the neural network-based waveform-to-symbol converter (NNWSC) for a coordinated multi-input and single-output (MISO) photonic millimeter-wave system with multiband multiplexing. The NNWSC replaces conventional matched filtering, down-sampling, and equalization, simplifying the receiver and enhancing interference resilience. Additionally, it reduces computational complexity, improving operational feasibility. As a proof of concept, experiments are conducted in a 16QAM non-orthogonal multiband carrierless amplitude and phase (NM-CAP) modulation system with coordinated MISO configurations in a scenario where two base stations have 5 km and 10 km fiber links, respectively. Data were collected across various roll-off factors, sub-band spacings, and received optical power (ROP) levels. Based on the proposed method, a coordinated MISO photonic millimeter-wave (mmWave) communication system at 91.9 GHz is demonstrated at a transmission speed of 30 Gbps. The results show that the NNWSC-based receiver achieves significant bit error rate (BER) reductions compared to conventional receivers across all configurations. The tolerances to the STO of NNWSC are also studied. These findings highlight NNWSC integration as a promising solution for high-frequency, interference-prone environments, with potential improvements for low-SNR and dynamic STO scenarios. Full article

Micro-drones weighing less than about 200 g have a limited flight time of 5–15 min. Dynamic charging by optical wireless power transmission is a promising solution to this problem. This paper investigated the configuration and conditions required for dynamic charging of micro-drones by optical wireless power transmission and clarified the effect of weight change on the power required for flight and the size of solar cells that can be installed. Furthermore, a micro-drone equipped with a solar cell without a battery was used to demonstrate a vertical flight height of 75 cm at 35 W light output. The results are useful for continuous flight of micro-drones by optical wireless power transmission. Full article

This paper presents an efficiency optimization method for laser wireless power transmission (LWPT) system, focusing on the coordination and control of multiple laser diodes. A distributed laser wireless power transmission (D-LWPT) system is proposed, which includes multiple independent and parallel power transmission chains. The system has the characteristics of power scalability, redundancy, and control flexibility. The efficiency characteristics of each key component in the LWPT system are discussed. Due to the internal losses of the laser, the transmission efficiency is also affected by the transmission power. For distributed architecture, its flexibility allows for the rational allocation of transmission power. To achieve optimal efficiency, a central scheduling controller is designed to regulate the current of LDs. A swarm intelligence-based optimization algorithm is used to determine the optimal operating current. This significantly improves the system’s efficiency and ensures real-time control. Experimental results validate the effectiveness of the proposed techniques. The DC to DC efficiency of the power transmission chain can reach over 14%, and the photovoltaic array can output a maximum power of over 130 W. The impact of beam combination on the efficiency and output power of PV arrays is less than 3%, indicating that the distributed structure does not affect system performance. The experimental results show that the proposed efficiency optimization method has excellent power following performance (algorithm execution time < 10 ms) and effective efficiency optimization performance. Under light load conditions, the LDs’ efficiency is optimized from 27.5% to 45.0%, and under medium load conditions, it is optimized from 41.5% to 44.5%. This distributed structure and efficiency optimization method provide a solution for improving the performance of LWPT systems. Full article

In biomedical research, telemetry is used to take automated physiological measurements wirelessly from animals, as it reduces their stress and allows recordings for large data collection over long periods. The ability to transmit high-throughput data from an in-body device (e.g., implantable systems, endoscopic capsules) to external devices can also be achieved by radiofrequency (RF), a standard wireless communication procedure. However, wireless in-body RF devices do not exceed a transmission speed of 2 Mbit/s, as signal absorption increases dramatically with tissue thickness and at higher frequencies. This paper presents the design of an optical wireless communication system (OWCS) for neural probes with an optical transmitter, sending out physiological data through an optical signal that is detected by an optical receiver. The optical receiver position is controlled by a tracking system of the small animal position, based on a cage with a piezoelectric floor. To validate the concept, an OWCS based on a wavelength of 850 nm for a data transfer of 5 Mbit/s, with an optical power of 55 mW, was demonstrated for a tissue thickness of approximately 10 mm, measured in an optical tissue phantom. Full article

This paper introduces a high-precision alignment method for laser wireless power transmission (LWPT) systems, integrating neural network-based target detection with a perturbation-observation technique. The objective is to enhance the alignment accuracy between the laser spot and the photovoltaic array, thereby improving energy transfer efficiency. The method’s key feature is its ability to achieve these results without requiring additional optical components, simplifying system design. Continual assessment and adjustment based on real-time output power data ensure optimal alignment, maximizing the photovoltaic array power output. Experimental results demonstrated that the proposed method achieved an initial alignment precision with pixel errors below 3%, translating to a physical error of approximately 7 mm. Fine-tuning through the perturbation-observation method further optimized the alignment, resulting in a photovoltaic array power output of 98.70% of its maximum potential. This hybrid approach provides a reliable solution for boosting the performance of LWPT systems, offering significant potential for practical applications. Full article