The data rate of a visible light communication (VLC) system is basically determined by the electrical-to-optical (E-O) bandwidth of its light-emitting diode (LED) source. In order to break through the intrinsic limitation of the carrier recombination rate on E-O bandwidth in conventional c-plane LEDs based on InGaN quantum wells, a blue micro-LED with an active region of nano-structured InGaN wetting layer is designed, fabricated, and packaged to realize a high-speed VLC system. The E-O bandwidth of the micro-LED can reach up to 1.3 GHz. Based on this high-speed micro-LED, we demonstrated a data rate of 2 Gbps with a bit error rate (BER) of 1.2 × 10 − 3 with simple on-off keying signal for a 3-m real-time VLC. In addition, a 4-Gbps VLC system using quadrature phase shift keying-orthogonal frequency-division multiplexing with a BER of 3.2 × 10 − 3 is also achieved for the same scenario. Among all the point-to-point VLC systems based on a single-pixel LED, this work has the highest distance-bandwidth product of 3 GHz·m and the highest distance-rate product of 12 Gbps·m.

Blue/green light-emitting diodes (LEDs) show great potential in medium/short distance underwater optical wireless communication (UOWC) while suffering limited bandwidth caused by a long radiative recombination carrier lifetime and large resistance–capacitance (RC) constant. We designed, fabricated, and packaged a 75-µm single-layer quantum dot (QD) blue micro-LED with a record high modulation bandwidth up to 1.03 GHz. The single-layer structure of QD reduces the carrier lifetime and RC delay. A data rate of 2 Gbps over a 3-m air–underwater channel using a non-return-to-zero on–off-keying modulation format with a low bit-error rate of 2 . 03 × 10 − 3 was achieved below the forward error correction limit, which is the highest data rate of micro-LED-based UOWC systems, to the best of our knowledge.

We experimentally demonstrated a high-speed multi-user green and blue laser diode based underwater optical wireless communication (UOWC) system using non-orthogonal multiple access (NOMA) with polarization multiplexing. The system affords eight users with a record sum rate of 18.75 Gbps over 2-m underwater plus 0.5-m free-space channel. The modulation bandwidths of four detachable optical paths with different wavelengths and polarization states all exceed 1.5 GHz. The results suggest that the flexible balance according to both user fairness and overall throughput/sum rate can be achieved via an appropriate power allocation strategy. The joint optimization of driving current and user assignment ensures the feasibility of providing stable high-speed UOWC for multiple users. With the proposed OFDMA-NOMA scheme, user scale expands by twice while the sum rate for single path reaches 3.2 Gbps. Finally, the BER performances of NOMA modality in turbulent underwater environment with air bubbles of different flow rates are also discussed in detail.

We propose and experimentally demonstrate a distributed digital pre-equalization (DPE) technique for orthogonal frequency division multiplexing (OFDM)-based bandlimited visible light communication (VLC) systems. In the VLC system applying distributed DPE, the subcarriers are divided into two bands, where the bandwidth and the power of each band can be flexibly adjusted to maximize the achievable data rate of the system. Hence, distributed DPE exhibits much higher tolerance against light-emitting diode (LED) nonlinearity than conventional centralized DPE. Experimental results verify the superiority of distributed DPE for OFDM-based bandlimited VLC systems. More specifically, a data rate of 976.6 Mbit/s is achieved by using distributed DPE, which corresponds to an achievable rate improvement of 25% in comparison to centralized DPE.

This article presents a novel scheme based on underwater optical wireless communication and positioning (UOWC-UOWP) for an underwater wireless sensor network (UWSN). A dual-hop system is adopted to extend the limited coverage area of the UWSN with mobile nodes, consisting of a grade-index plastic optical fiber (GI-POF) link and a wireless link. Specifically, the mini-LED offers high-speed and flexible uplink transmission and the high-power LED enables both downlink transmission and positioning. The time frame design and code division multiplexing access (CDMA) support multi-user signal transmission. Proof-of-concept experiments with GI-POF and wireless link demonstrate the feasibility of the proposed scheme, which offers full-duplex communication, high-precise positioning and extended distance. To the best of our knowledge, the UOWC-UOWP convergent system is proposed for the first time. It has great potential to support high-capacity transmission between mobile nodes for future underwater transmission scenarios.