Broadband Compact Silicon Wire to Silicon Slot Waveguide Orthogonal Bend

An ultra-compact 90° bend between silicon (Si) wire and silicon slot waveguide (SSW) with a footprint of ~725 nm × 500 nm is experimentally demonstrated on silicon-on-insulator substrate. By achieving momentum matching of the waveguides through an orthogonal junction placement, and maximizing modal overlap through an angled facet, coupling efficiency of ~70% and 3-dB bandwidth of over 500 nm has been achieved. The nominal experimental transmission through cascaded input (Si wire to SSW) and output (SSW to Si wire) orthogonal junctions match closely those obtained from simulations, both in the range from 1270 to 1360 nm and from 1480 to 1590 nm. For slot widths ranging from 30 to 230 nm, our Si wire-SSW bend can achieve coupling efficiency comparable to that of a direct butt-coupler over a 400 nm bandwidth. This compact and wideband waveguide bend serves as an important component to enable dense integration between conventional Si wire and SSW.