On-Fiber Diffractive Beam Splitter for Multi-Core Fiber Interfacing Fabricated by Two-Photon Polymerization

Abstract

We present a monolithic diffractive beam splitter (DFBS) directly fabricated on a single-mode fiber facet using two-photon polymerization direct laser writing. The device enables compact single-core to multi-core fiber coupling through free-space beam shaping, integrating a microstructured optical fiber-based mode expander, a diffractive beam-splitter, and collimating-focusing diffractive optical elements within a 355 μm-long structure. Operating at 1550 nm, the DFBS splits the input beam into seven collimated outputs matching a typical seven-core fiber layout. Simulations achieved a 72% conversion efficiency and <1% intensity variation, while experimental results confirmed functional multi-beam projection and good fabrication repeatability. The approach demonstrates a scalable route towards miniaturized, fiber-integrated optical interfaces for spatial-division multiplexing and lab-on-fiber applications, supporting future co-packaged photonic systems.