State-of-the-art for high-speed visible light laser communication

In recent years, visible light communication (VLC) has gained attention as a promising solution to mitigate the scarcity of spectrum resources and channel capacity issues in 6G. Light emitting diodes (LEDs), super luminance diodes (SLDs) and laser diodes (LDs) can serve as the light sources in VLC systems. Over the years, LEDs have been widely utilized in VLC systems due to lower cost and reduced risk to human eyes. However, the LD-based VLC is becoming increasingly attractive to achieve ultra- high-speed and long-distance applications due to its advantages over LEDs and SLDs such as high modulation bandwidth, high coherence, precise beam focusing, and narrow linewidth. This paper provides a summary of the latest advances in high-speed and long-distance visible light laser communication (VLLC), with maximum data rates exceeding 500Gbps and distances up to 100m, as well as the corresponding challenges and prospects. In addition, an overview of the VLLC system is provided, including devices, modulation, signal processing, channels, and networking. This paper also introduces the design of the 50-channel wavelength division multiplexing (WDM) VLLC system achievingthe date rate over 500Gbps.