In recent studies, visible light communication (VLC) has been predicted to be a prospective technique in the future 6G communication systems. To suit the trend of exponentially growing connectivity, researchers have intensively studied techniques that enable multiple access (MA) in VLC systems, such as the MIMO system based on LED devices to support potential applications in the Internet of Things (IoT) or edge computing in the next-generation access network. However, their transmission rate is limited due to the intrinsic bandwidth of LED. Unfortunately, the majority of visible light laser communication (VLLC) research with beyond 10 Gb/s data rates concentrates on point-to-point links, or using discrete photodetector (PD) devices instead of an integrated array PD. In this paper, we demonstrated an integrated PD array device fabricated with a Si-substrated GaN/InGaN multiple-quantum-well (MQW) structure, which has a 4×4 array of 50 μm×50 μm micro-PD units with a common cathode and anode. This single-integrated array successfully provides access for two different transmitters simultaneously in the experiment, implementing a 2×2 MIMO-VLLC link at 405 nm. The highest data rate achieved is 13.2 Gb/s, and the corresponding net data rate (NDR) achieved is 12.27 Gb/s after deducing the FEC overhead, using 2.2 GHz bandwidth and superposed PAM signals. Furthermore, we assess the Huffman-coded coding scheme, which brings a fine-grain adjustment in access capacity and enhances the overall data throughput when the user signal power varies drastically due to distance, weather, or other challenges in the channel condition. As far as we know, this is the first demonstration of multiple visible light laser source access based on a single integrated GaN/InGaN receiver module.

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.

In this paper, we studied a series of high-speed photodetectors (PD) with different super-lattice interlayer periods and the scale of the effective area to examine their communication performance. The mini-PDs are designed with a single 1 mm × 1 mm effective area. The mini-PDs have three different super-lattice (SL) periods in the interlayer: 8, 15, and 32. The micro-PD sample has multiple 50um by 50um photosensitive areas that form a 4 × 4 receiver array, which shares a common N electrode. Its SL period is 26. The experiment shows that mini-PDs have the advantages such as better tolerance to beam spot deviation, larger field of view (FoV), higher responsibility, and wider peak width in spectral response. But micro-LED samples outperform the others in communication capacity and wavelength selectivity. The 8, 15, and 32 SL mini-PD samples achieve 6.6, 7.3, and 8.8 Gb/s data rates, respectively. The micro-PD gains the maximum data rate of 14.38Gb/s without applying waveform level post-equalization, and 15.26Gb/s after using an NN-based post-equalizer. This experiment shows that with proper DSP, GaN-based PD would be suitable for high-speed VLC systems, especially for the short wavelength spectrum in visible light.

Visible light communication (VLC) has emerged as a valuable addition to the existing spectrum for wireless communication, complementing traditional radio frequency (RF) communication. By utilizing the untapped spectrum of visible light, VLC has the potential to play a substantial role in advancing wireless communication technologies. Nonetheless, it is worth noting that the predominant research focused in LED-based visible light communication has primarily revolved around point-to-point communication or the more ideal multiple-input multiple-output (MIMO) system. In this article, a transmission matrix-assisted neural network (TMANN) is proposed for a 2 × 4 MIMO visible light communication system to implement MIMO demultiplexing. The 2 × 2 transmission matrix is estimated by three methods, including the preamble method, the least mean-squares MIMO (LMS-MIMO) method, and the proposed attention-based weight neural network (AttWNN) method. The performance of transmission matrix estimation methods has been thoroughly investigated through both simulation and experimental evaluations. During the experiments conducted, it is observed that without employing any MIMO demultiplexing techniques, the total transmission rate can only achieve 2.787 Gbps, while by utilizing the classical least mean-squares MIMO (LMS-MIMO) method, the transmission rate can significantly increase to 5.961 Gbps. Compared with a multi-branch hybrid neural network (MBNN), the proposed TMANN has a full 59.23% reduction in computational complexity, although there is only a slight increase in data rate (from 6.643 Gbps to 6.689 Gbps). To the best of our knowledge, this is the highest transmission rate achieved in a LED-based MIMO visible light communication system in the simultaneous transmission of two data channels. These results showcase the promising applications of our proposed TMANN in low-cost MIMO visible light communication systems.

Despite an increasing number of researches focused on the photo-biological effects of lighting on visual and non-visual health, insights into the phosphor-free white LED lamps with different spectral power distributions remain unclear. In this study, human factors experiments were conducted with 30 participants. Variations in ocular physiological parameters and melatonin circadian rhythms were assessed for participants in an ordinary lamp, a full-spectrum lamp, and four phosphor-free white LED lamps rich in the 535–589 nm yellow-green light. It was observed that ocular functions exhibited significantly higher improvements under the four phosphor-free LED lamps compared to the ordinary and full-spectrum lamps, indicating the advantageous effects of phosphor-free lamps rich in the 535–589 nm yellow-green light on both visual and non-visual health.