3D direct laser writing of microstructured optical fiber tapers on single-mode fibers for mode-field conversion.

We present a design and fabrication approach for 3D printed polymer microstructured optical fiber tapers on standard single-mode glass fibers for efficient and compact mode-field conversion. This paves the way towards complex functionalized fiber tips for various applications, like sensors and beam shaping components, currently limited by the mode-field size and distribution of standard optical fibers. In this paper, we demonstrate the potential of mode-field converting tapers for relaxing the misalignment tolerance in fiber-to-fiber connections and maximizing the coupling efficiency in fiber-to-chip connections. We demonstrate a mode-field diameter expansion ratio of 1.7 and reduction ratio of 3 and show that our microstructured tapers achieve a comparable performance in coupling efficiency as their step-index counterparts, while providing greater robustness.