Interconnected counter-propagating recirculating loops with high-loss loop back path for long-haul integrated sensing and communication in-lab emulation

The integration of high-speed optical communication and distributed sensing could bring intelligent functionalities to ubiquitous optical fiber networks, such as seismic detection, while in the face of a major challenge of constructing a long-haul thousand-kilometer fiber link. This work proposes the first, to our knowledge, interconnected counter-propagating recirculating loop (ICP-RL) with high-loss loop back (HLLB) path as a compact in-lab platform for ultra-long-haul integrated sensing and communication (ISAC), and experimentally demonstrates a simultaneous 32-GBaud PMD-QPSK signal transmission and distributed acoustic sensing (DAS) system application with a spatial resolution of 3.3 km over 3651-km SSMF. The recirculating loop is controlled by acoustic-optical modulators, which also provide an essential frequency shift for the Rayleigh backward scattering sensing signal distinction. The proposed ICP-RL makes possible a low-cost in-lab validation platform for long-haul ISAC systems during the research and development (R&D) phase.