Forward polarization sensing triggered area-focus DAS over a bidirectional coherent network.

Empowering optical communication networks with sensing capabilities is an emerging trend. In this Letter, we propose a method to preliminarily detect perturbations in a bidirectional coherent network by utilizing forward polarization information. This information acts as a trigger and provides prior knowledge to back-scattering-based distributed acoustic sensing (DAS), enabling more detailed event recovery. Consequently, the need to keep DAS continuously active is eliminated, making it highly practical for long-haul, high-resolution DAS sensing networks. Once activated, DAS can focus on a preliminary area of interest, significantly reducing its data processing workload. Experimentally, we employ a commercial 200-kHz laser to simultaneously achieve bidirectional 60-GBaud 16-QAM transmission and forward polarization sensing. The forward sensing information, extracted through equalization taps, triggers area-focused DAS, enabling fine-grained and ultra-low complexity sensing. This seamless integration of communication and sensing functions enhances efficiency and reduces complexity, paving the way for advanced network applications and more effective network surveillance capabilities.