In-line Monitoring of Multi-Core Fibers by 3D Polymer Waveguides

Space-division multiplexing (SDM) based on multi core fibers (MCFs) has emerged as a critical technology to overcome the capacity limits of traditional single-mode fiber networks driven by artificial intelligence (AI), 6G, and big data applications. Ensuring the reliability of such systems requires real time signal monitoring. However, current solutions suffer from bulky discrete architectures and high integration costs. To address this, this paper presents a three-dimensional (3D) polymer waveguide chip for 7-core fibers that monolithically integrates fan in/fan-out (FIFO) capability with low-invasiveness signal tapping. The fabricated device achieves a total insertion loss of < 5.4 dB at 1550 nm, while tapping approximately 4% of the optical power for monitoring. This integrated approach provides a practical, scalable route for on-chip, real-time management of next generation SDM systems.