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.

With the advent of the sixth-generation mobile communication standard (6 G), the visible light communication (VLC) technology based on wavelength division multiplexing (WDM) technology can effectively solve the problem of shortage of spectrum resources and insufficient channel capacity. This paper introduces one of our technical achievements, namely the construction of a near-real-time visible light laser communication (VLLC) system based on WDM, which includes a self-designed 10-λ fully-packaged visible light laser emission module, 1 m multimode fiber – 0.175 m free space – 1 m multimode fiber optical transmission link, and receiver array. In the transmitter system, we adopt adaptive discrete multitone (DMT) modulation technique combined with Quadrature Amplitude Modulation (QAM) modulation scheme to obtain maximum spectral efficiency (SE). In the receiving system, we utilize the sparse-structured reservoir computing post-equalization algorithm to achieve superior equalization performance on the basis of the traditional post-equalization algorithm. The experimental results indicate that this quasi-real-time communication system has achieved a signal transmission rate of 113.175Gbps. To the best of our knowledge, this work has set a record in the field of high-speed visible light laser communication. Therefore, the laser communication system constructed by this work, with its flexibility in deployment and high-speed performance, demonstrates the significant potential application of visible light laser communication in data center interconnection and high-speed indoor access networks.

Underwater visible light communication (UVLC) based on LEDs has become a competitive candidate, which is able to provide high data rates, low latency and low cost for next-generation wireless communication technologies. However, it is still challenging to achieve high-speed communication because of bottleneck problems such as bandwidth limitation and linear and nonlinear distortions. Traditional Deep-learning Neural Network (DNN)-based waveform-to-symbol converter is verified to be an effective method to alleviate them, but impractical due to high complexity. To achieve a better tradeoff between communication performance and computation complexity, a cascaded receiver consisting of a DNN-based waveform-to-symbol converter and modified Neural Network (NN)-based decision-directed least mean square (DD-LMS) is then innovatively proposed. With fewer taps and nodes than the traditional converter, the front-stage converter could mitigate the majority of Inter-Symbol Interference (ISI) and signal nonlinear distortions. Then modified NN-based DD-LMS is cascaded to improve communication performance by reducing phase offset, making received constellation points more concentrated and closer to standard constellation points. Compared with the traditional converter, the cascaded receiver could achieve 89.6% of signal Vpp dynamic range with 12.4% of complexity in the 64APSK UVLC system. Moreover, the ratio of signal Vpp dynamic range and total trainable parameters is 1.24 × 10⁻¹ mV, while that of the traditional converter is 1.95 × 10⁻² mV. The cascaded receiver used in 64APSK UVLC systems is experimentally verified to achieve enhanced performance, thus as a promising scheme for future high-speed underwater VLC.

The sixth-generation mobile communication is committed to creating a large-capacity, low-latency, three-dimensional communication network encompassing space, air, land, and sea. Visible light communication (VLC) uses carriers with wavelengths from 380 nm to 760 nm for information transmission, offering a spectrum of 400 THz. Besides, visible light falls within the underwater transmission window, which offers significant potential for sea-based communication network construction. However, underwater visible light communication (UVLC) faces the effects of turbulence, device nonlinearity, attenuation, and noise, which limit the increase of the capacity of UVLC. To address the effects of turbulence, considering that turbulence has different effects on different polarization directions, the received signal can be better reconstructed by increasing the observation dimension, like observing the signal in multiple polarization directions. We proposed the use of circularly polarized light for transmission with a dual-aperture receiver, where the dual apertures detect the horizontally and vertically polarized components of the light beam, respectively. For the fusion of the two received signals, and in order to resist undesirable factors such as device nonlinearity and high-frequency attenuation, we designed a sparse dual-polarization triple-branch network (S-DPTBN) for signal reconstruction and recovery. The sparsification reduces the complexity and improves the robustness of the network, and the triple-branch design can fully extract the information of the horizontal and vertical polarizations as well as the weighted sum of the two. To enhance the communication capacity, we integrated an 8-wavelength laser emission module for signal transmission. Finally, experimental results confirmed that the proposed system achieved data rates of 144.90 Gbps, 143.50 Gbps, and 140.70 Gbps in conditions of no turbulence, medium turbulence, and strong turbulence, respectively, which had an improvement of 14.00 Gbps, 14.00 Gbps, and 13.30 Gbps over traditional point-to-point systems with deep neural network-based equalizers.