Metal–Insulator–Silicon–Insulator–Metal Waveguide Splitters With Large-Arm Separation

Symmetric 1 × 2 splitters of metal-insulator-silicon-insulator-metal (MISIM) waveguides, which are hybrid plasmonic waveguides with a 190-nm-wide silicon strip covered by 30-nm-thick SiO₂ and sandwiched by copper, are theoretically and experimentally investigated. The splitters consist of a Y-branch, two 90° submicrometer-radius bends (SRBs), and two straight MISIM waveguides connecting the Y-branch and the two SRBs. The Y-branch is an overlap of two oppositely directed SRBs. All the SRBs of the splitter have the same radius of curvature. The splitter has a feature that the length of the in-between MISIM waveguides is adjusted to make its input waveguide split over a short distance into its widely separated output waveguides. Simulation of the splitters indicates that the radius of curvature of the SRB needs to be ≥ 0.8 μm to make small the excess losses of the splitters. When the radius of curvature is 0.8 μm, the splitter which can connect its input waveguide just over 1.6 μm to its output waveguides spaced 6.4 μm apart has an excess loss of 1.4 dB. The splitters are realized by using the standard CMOS technology. The measured excess losses of the fabricated splitters are larger than the calculated excess losses. However, the measured dependence of the excess loss on the radius of curvature is similar to the calculated one. Finally, the splitter feature is theoretically confirmed, and the addition of a tapering region to the Y-branch is discussed to reduce the excess loss of the Y-branch.