Small radius bends and large angle splitters in SOI waveguides

The silicon/silicon dioxide (Si/SiO2) materials system provides a high index contrast waveguide platform compatible with existing monolithic microelectronic fabrication processes. The large index difference between the Si and SiO2 (Delta n approximate to 2.0) allows the miniaturization of waveguide cross-sectional dimensions: single-mode strip waveguides with 0.2 x 0.5 mu m cross-sections are possible. Additionally, right angle waveguide bends with radii of 2.0 mu m can be fabricated with insertion loss of less than 1.0 dB. Bend radii of 250 mu m or more are required to achieve the same performance in less confined waveguide systems such as GaAs/AlGaAs. The high confinement of the Si/SiO2 system also allows Y-branch power splitters with splitting angles greater than 20 degrees to operate with low loss. The combination of small cross-section, small bend radius, and large splitting angle provides a highly compact light guiding technology. Calculations of the loss due to 90 degrees bends in these waveguides and preliminary loss measurements for bends from 2.0 to 100.0 mu m in radius are reported. Y-branch power splitters are analyzed and measurements of branches from 2 degrees to 40 degrees are presented.