Silicon-on-insulator optical rib waveguides: loss, mode characteristics, bends and y-junctions

Optical rib waveguides with widths from 2.73 to 7.73 microns have been formed in SIMOX-based silicon-on-insulator (SOI) structures consisting of a 4.32 micron thick surface-silicon layer and a 0.398 micron buried-oxide layer. The effect of waveguide width, bend radius, y-junction splitting and interface roughness on loss and mode characteristics have been studied at wavelengths of 1.15 and 1.523 microns. The experimental results support the hypothesis that certain rib dimensions can lead to single-mode waveguides even though planar SOI waveguides of similar multimicron dimension are multimode. The propagation losses of waveguides 3.72 microns wide were found to be nominally 0.0 dB/cm and 0.4 dB/cm for the TE and TM modes, respectively, when measured at 1.523 microns, where the measurement error was ±0.5 dB/cm. This means that the loss is experimentally indistinguishable from pure bulk silicon. These results are thought to be the lowest loss measurements for silicon integrated optical waveguides reported to date