High speed light emitting diode (LED) based visible light communication (VLC) system is restricted by the limited LED bandwidth, low detector sensitivity, linear and nonlinear distortions. Thus, single and two cascaded constant-resistance symmetrical bridged-T amplitude hardware pre-equalizers, carrier-less amplitude and phase (CAP) modulation and a three-stage hybrid post-equalizer are investigated to increase transmission data rate for a high speed LED based VLC system. The schemes utilized by the hybrid post-equalizer are modified cascaded multi-modulus algorithm (M-CMMA), Volterra series based nonlinear compensation algorithm and decision-directed least mean square algorithm (DD-LMS). With these technologies, we successfully implement high speed CAP32, CAP64 and CAP128 VLC experimental system over 1m free space transmission with bit error rate (BER) under the hard decision-forward error correction (HD-FEC) threshold of $3.8\times 10^{-3}$. System performance improvement employing these key technologies is also validated through experimental demonstration. With the superposition of each stage of the hybrid post-equalizer, system performance will be improved. And utilizing two cascaded hardware pre-equalizer will provide more accurate channel compensation than single pre-equalizer.

Compared with multicolor-chip integrated white LEDs, phosphor-based white LEDs are more attractive for daily illumination due to lower cost and complexity, and thus they are preferable for future commercial use of visible light communication (VLC) systems. However, the application of phosphorescent white LEDs has a lower data rate than multicolor-chip integrated LEDs because of severe nonlinear impairments and limited bandwidth caused by the slow-responding phosphor. In this paper, for the first time we propose to employ phosphorescent white LEDs based on silicon substrate with adaptive bit-loading discrete multitone (DMT) modulation and a memoryless polynomial based nonlinear equalizer to achieve a high-speed VLC system. We also present a comprehensive comparison among nonlinear equalizers based on the Volterra series model, memory polynomial model, memoryless polynomial model and deep neural network (DNN) with experimental results utilizing a silicon substrate phosphorescent white LED, and provide detailed suggestions on how to choose the most suitable nonlinear mitigation scheme considering different practical conditions and the tradeoff between complexity and performance. Beyond 3.00 Gb/s DMT VLC transmission over 1-m indoor free space is successfully demonstrated with bit error rate (BER) under the 7% forward error correction (FEC) limit of 3.8×10⁻³. As far as we know, this is the highest data rate ever reported for VLC systems based on a single high-power phosphorescent white LED.

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.