Silicon‐Nitride‐Based Laser Directly Driving Computationally Lightweight 600 Gbps/λ Optical Transmission

Driven by 6G connectivity and AI computing, coherent optical transmission is expanding beyond long‐haul networks toward a broad range of lightweight links. Silicon photonic devices, particularly integrated lasers, offer advantages in ultra‐high capacity, and low power consumption. However, their practical deployment remains hindered by the gain‐noise trade‐off, as well as the huge coherent digital signal processing (DSP) consumption. To address this challenge, we report an integrated Si 3 N 4 ‐based laser unifying high power, high coherence, and wide tunability, enabling high‐capacity, computationally lightweight optical transmission. It integrates a dual‐external‐cavity laser with an extended semiconductor optical amplifier (SOA), featuring a high‐Q subwavelength‐defect‐assisted microring for considerable linewidth reduction despite SOA degradation. The demonstrated laser maintains an intrinsic linewidth below 20 Hz @ 50 mW across 53 nm wavelength range, and presents a maximum fiber‐port output power of 171 mW. It directly drives coherent optical transmission with a line rate of up to 600 Gbps per wavelength. Furthermore, we highlight its low‐linewidth property for reducing carrier phase estimation computation in coherent DSP to 10 −5 compared to using commercial tunable lasers. This work paves the way toward computationally lightweight optical transmission, opening new opportunities for data‐center interconnects, inter‐satellite links and beyond.