Fabrication for Y-branched Polymer Optical Waveguide Using the Imprint Method and Its Application for Mode Division Multiplexing Devices

We propose an asymmetric polymer Y-branched waveguide for a multiplexer of TE
01
and TE
11
modes to a few-mode fiber in mode division multiplexing links, in this paper. Fabricated waveguides have square cross-sectional graded-index (GI) cores which exhibit strong optical confinement to the core center. Theoretical loss calculation by BPM shows that the GI core exhibits higher mode splitting ratio and about 1 dB lower insertion loss than the conventional SI core. The measurement results of the fabricated waveguide elucidate that the GI core shows an insertion loss about 1.5 dB lower than the SI core, showing a more pronounced low loss advantage. We also demonstrate in this paper that a square approximation for the core cross-section allows to reduce the coupling loss with fibers and realize a low-loss mode multiplexer, compared to the rectangular cross-sectional core.