21.79/17.49 Gbps Full-Duplex Visible Light Communication Enabled by Short-Cavity Blue and Green InGaN/GaN Laser Diodes

Future 6G communication includes underwater and cross-media scenarios, in which visible light laser communication (VLLC) has inherent advantages such as large capacity and transmission security. GaN-based laser diodes (LDs) are expected to play important roles in future VLLC systems, leveraging their capability in short-wavelength visible light spectrum, especially in the blue-green transmission window of water. Large bandwidth, high-speed blue/green laser devices could provide desirable channel capacity for wavelength-division full-duplex communication systems. In this paper, through theoretical analysis based on the bandwidth formula of LDs derived from the carrier rate equation, combined with numerical calculations, we design blue and green InGaN/GaN Fabry–Pérot (FP) cavity LD structures to increase bandwidth. High-bandwidth blue and green LDs for short-distance high-speed communication are fabricated by simultaneously shortening cavity length, reducing waveguide layer thickness, and increasing end-face reflectivity. The blue and green LDs achieve the −3dB E-E bandwidth of 5.4 GHz and 3.5 GHz, respectively, enabling a 21.79/17.49 Gbps full-duplex system with 21.79 Gbps downlink and 17.49 Gbps uplink using the discrete multi-tone (DMT) bit-loading modulation format. These results set a record for bandwidth and communication rate in blue and green VLLC full-duplex systems, paving the way for future high-speed applications in visible light wireless access infrastructures.