400 Gb/s coherent fiber-optic integrated sensing and communication with LFM optical carrier reuse

A coherent fiber-optic integrated sensing and communication (F-ISAC) system with linearly frequency-modulated (LFM) optical carrier reuse is experimentally demonstrated over standard single-mode fiber. In the proposed scheme, a communication signal carried by an LFM optical carrier is coupled with an unmodulated LFM optical carrier to form an integrated sensing and communication (ISAC) signal. The unmodulated LFM carrier is reused as both an in-band phase-noise reference for coherent communication and the distributed acoustic sensing (DAS) probe. By using this reference, the local-oscillator (LO) phase noise can be compensated, enabling cost-effective coherent receiving with a large-linewidth LO, while the same carrier generates the Rayleigh backscattering signal for DAS. Experiments demonstrate single-wavelength 400-Gb/s coherent transmission over 82 km using an approximately 5-MHz-linewidth LO, together with DAS operation with 5-m spatial resolution and 208-pε/sqrt(Hz) strain sensitivity. Compared with DAS using a pure LFM probe, only a 1.4-dB sensing penalty is introduced. Moreover, the carrier-to-signal power ratio-dependent communication-sensing trade-off is characterized, providing a flexible power-allocation guideline for coherent F-ISAC links.