Ultracompact 3D Splitter for Single-Core to Multi-Core Optical Fiber Connections Fabricated Through Direct Laser Writing in Polymer

The deployment and advancement of high-bandwidth communication networks, quantum information systems, and sensing platforms relying on multi-core optical fibers (MCFs) are challenged by the scarcity of cost-effective, compact, and efficient optical interfacing components. This study introduces an unprecedented 3D-printed 1 × 4 splitter for MCFs fabricated with 2-photon polymerization-based direct laser writing. The pivotal element is a triangular cross-section 3D multimode interference (MMI) coupler, supplemented with S-bends and adiabatic tapers to facilitate the splitting of a signal from a single core of a single-mode fiber into four cores of a multi-core fiber. All components are initially designed and assessed to minimize loss and polarization dependence across the C- and L-bands using optical simulation. Subsequently, a proof-of-concept model of the splitter, compactly integrated within the fiber volume, featuring a remarkably short length of 180 µm and insertion loss of ≈−3 dB, is fabricated. The manufacturing speed, minimal loss, component compactness, and flexibility of the approach, collectively present promising avenues for pioneering developments in MCF-coupling components.