Analysis of Polarization-Splitting Characteristics in Three-Core-Based Directional Couplers Using Silicon Hybrid Plasmonic Waveguides

The polarization dependent nature of a central waveguide in a three-core directional coupler plays a key role in splitting polarized guided modes onto different layers of 3-D silicon photonic circuits. Here, we investigate the dependence of beam splitting characteristics on the central hybrid plasmonic waveguides. We used three Si-based hybrid long-range surface plasmon polariton (LR-SPP) waveguides: a Si-M-Si, a Si-SiO₂-M-Si, and a Si-SiO₂-M-SiO₂-Si waveguide, where M is a metal or an emerging plasmonic material. Numerical simulations revealed that the device using a symmetric LR-SPP waveguide structure provided the most satisfactory optical characteristics. On the entire C-band, the extinction ratios for 3-D and 2-D polarization beam splitting were larger than 20 dB and the insertion losses were less than 0.25 dB. Based on theoretical investigations, we suggest some design guidance for the proposed three-core-based 3-D polarization beam splitters using a Si-based hybrid LR-SPP waveguide.