Silicon photonics provides a unified solution for all-distance optical communications

Optical links underpin global communications from chip-to-chip interconnects to transoceanic fibre networks. Conventional architectures remain distance-dependent: long-haul systems rely on coherent transmission for high spectral efficiency and capacity, while short-reach links favour intensity modulation due to hardware complexity and power constraints. This divide impedes scalability for AI-driven intra-data-centre traffic and low-latency, flexible cloud-to-edge connectivity. Here we demonstrate a unified silicon photonic coherent solution for all-distance optical communications. By employing an ultralow-loss silicon nitride external cavity, we achieve 70 mW of direct laser output with a sub-kHz linewidth and 13.7% wall-plug efficiency. Paired with silicon photonic transceivers, this platform enables short-distance transmission without optical amplification across 256 wavelength channels, corresponding to an aggregate data rate of 81.92 Tb/s, as well as transmission exceeding 4400 km. It also supports wavelength switching and transmission re-establishment at tens-of-microseconds timescales. These results indicate the potential to simplify optical interfaces and enable flexible wavelength-routed connectivity. The authors demonstrate a silicon-photonic coherent platform using a high-power tunable laser and silicon-photonic transceivers, enabling broadband unamplified short-reach transmission, links beyond 4400 km and rapid wavelength switching.