Sub-picosecond synchronized multi-faceted fronthaul with one-sample-per-symbol coherent detection

High-precision synchronization, empowering sub-centimeter positioning and simplified digital signal processing (DSP), is essential for next-generation multifunctional, high-capacity and energy-efficient fronthaul networks. However, simultaneously achieving sub-picosecond time synchronization and high-throughput fronthaul transmission within a unified network remains a technical challenge. Here, we propose an electro-optic comb-based bidirectional fronthaul architecture that seamlessly integrates advanced telecommunication and time-frequency synchronization. Pilot comb lines, acting as high-fidelity carriers for clock delivery, are bidirectionally transmitted, enabling real-time phase drift compensation and achieving 0.25 ps root-mean-square time synchronization stability. Meanwhile, the forward pilots also facilitate remote-site comb regeneration, providing local oscillators for self-homodyne detection. Moreover, by harnessing this dual capability, we achieve network-synchronous one-sample-per-symbol coherent detection at the Nyquist limit across all parallel channels, eliminating carrier-phase and sampling-clock-related DSP while substantially reducing the complexity of analog-to-digital conversion and the remaining DSP. Our proposed architecture offers a scalable prototype for 6G multifunctional coherent-lite fronthaul networks. The work demonstrates an electro-optic comb-based fronthaul architecture that unifies subpicosecond time-frequency synchronization with high-capacity transmission, enabling energy-efficient one-sample-per-symbol coherent detection for 6G networks.