Visible light communication (VLC) is a highly promising complement to conventional wireless communication for local-area networking in future 6G. However, the extra electro-optical and photoelectric conversions in VLC systems usually introduce exceeding complexity to communication channels, in particular severe nonlinearities. Artificial intelligence (AI) techniques are investigated to overcome the unique challenges in VLC, whereas considerable obstacles are found in practical VLC systems applied with intelligent learning approaches. In this paper, we present a comprehensive study of the intelligent physical and network layer technologies for AI-empowered intelligent VLC (IVLC). We first depict a full model of the visible light channel and discuss its main challenges. The advantages and disadvantages of machine learning in VLC are discussed and analyzed by simulation. We then present a detailed overview of advances in intelligent physical layers, including optimal coding, channel emulator, MIMO, channel equalization, and optimal decision. Finally, we envision the prospects of IVLC in both the intelligent physical and network layers. This article lays out a roadmap for developing machine learning-based intelligent visible light communication in 6G.

Advancements in the semiconductor industry have enabled wearable devices to be used for a wide range of applications, including personalised healthcare. Novel energy harvesting technologies are therefore necessary to ensure that these devices can be used without interruption. Crystalline silicon photovoltaic (PV) cells provide high energy density to electronic loads. However, the optimization of these cells is a complex task since their optical performance is coupled to the surroundings, while their electrical performance is influenced by the intrinsic PV characteristics and parasitic losses. Without doubt, simulation tools provide the necessary insight to PV cell performance before device fabrication takes place. However, the majority of these tools require expensive licensing fees. Thus, the aim of this article is to review the range of non-commercial PV simulation tools that can be used for wearable applications. We provide a detailed procedure for device modelling and compare the performance of these tools with previously published experimental data. According to our investigations, non-commercial 3D tools such as PC3D provide accurate simulation results that are only ≈1.7% different from their commercial counterpart.

The rapid development of emerging technologies has led to a significant increase in data traffic, posing challenges for data centers in terms of storing, transmitting, and processing large volumes of information. Intra- and inter-datacenter connections with high bandwidth, low latency, high reliability, and high energy efficiency are in great demand. Traditional electrical communication is becoming increasingly inadequate, while optical communication has emerged as promising solutions. Visible light laser communication (VLLC) utilizes the spectrum ranging from 380nm to 700nm and has the advantages of offering high transmission rates, cost-effectiveness, and simple system structures. In this paper, enabling technologies including high-bandwidth laser diodes, advanced modulation formats, and artificial intelligence (AI)-based equalization schemes are introduced. A compact 50-channel VLLC interconnect system has been developed, achieving ultra-high-speed short-range VLLC transmission with a record data rate of 534.51Gbps, showcasing the potential of VLLC as a high-capacity and cost-effective optical intra-data center connection solution.

Although the 5G wireless network has made significant advances, it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras. As a result, emerging technologies in higher frequencies including visible light communication (VLC), are becoming a hot topic. In particular, LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing (WDM) technology. This paper proposes an optimized multi-color LED array chip for high-speed VLC systems. Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency, especially in the “yellow gap” region, and it achieves significant improvement in data rate compared with earlier research. This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model, which provides an explanation of the simulation and experiment results. In the final test using a laboratory communication system, the data rates of eight channels from short to long wavelength are 3.91 Gb/s, 3.77 Gb/s, 3.67 Gb/s, 4.40 Gb/s, 3.78 Gb/s, 3.18 Gb/s, 4.31 Gb/s, and 4.35 Gb/s (31.38 Gb/s in total), with advanced digital signal processing (DSP) techniques including digital equalization technique and bit-power loading discrete multitone (DMT) modulation format.

The application of high-speed micro-scale light-emitting diode (micro-LED) technology in short-distance data transmission breaks through the limitations of traditional electrical connections. This is particularly crucial as the demand for large-capacity and high-speed communications becomes more urgent, with a high-speed micro-LED light source being a key component. In this work, the alternating growth interruption method is used to grow a 3-layer InGaN nanostructure with smaller size and higher density. This approach increases local carrier concentration and reduces differential carrier lifetime. Based on the 3-layer improved InGaN nanostructure, a blue micro-LED is designed and fabricated, achieving the output optical power exceeding 0.5 mW while the electro-electric (E-E) −3 dB bandwidth exceeding 2.6 GHz. Utilizing this high-speed micro-LED as the light source, three non-return-to-zero on-off keying (NRZ-OOK) real-time communication systems are demonstrated: single-channel transmission via free-space and quartz optical fiber, and 4-channel transmission via plastic imaging fiber, achieving data rates of 3.07, 2.60, and 12.00 Gbps, respectively. Additionally, the 4-channel system achieves bit-power loading discrete multi-tone (DMT) transmission of 15.05 Gbps.

Future 6G communication includes underwater and cross-media scenarios, in which visible light laser communication (VLLC) has inherent advantages such as large capacity and transmission security. GaN-based laser diodes (LDs) are expected to play important roles in future VLLC systems, leveraging their capability in short-wavelength visible light spectrum, especially in the blue-green transmission window of water. Large bandwidth, high-speed blue/green laser devices could provide desirable channel capacity for wavelength-division full-duplex communication systems. In this paper, through theoretical analysis based on the bandwidth formula of LDs derived from the carrier rate equation, combined with numerical calculations, we design blue and green InGaN/GaN Fabry–Pérot (FP) cavity LD structures to increase bandwidth. High-bandwidth blue and green LDs for short-distance high-speed communication are fabricated by simultaneously shortening cavity length, reducing waveguide layer thickness, and increasing end-face reflectivity. The blue and green LDs achieve the −3dB E-E bandwidth of 5.4 GHz and 3.5 GHz, respectively, enabling a 21.79/17.49 Gbps full-duplex system with 21.79 Gbps downlink and 17.49 Gbps uplink using the discrete multi-tone (DMT) bit-loading modulation format. These results set a record for bandwidth and communication rate in blue and green VLLC full-duplex systems, paving the way for future high-speed applications in visible light wireless access infrastructures.