Sharply bent optical waveguide silicon-on-insulator substrate

We fabricated optical waveguides with a relative refractive index difference of maximally 45 percent on a silicon-on-insulator (SOI) substrate. We designed the Si channel using the finite difference time domain simulation and fabricated using electron beam lithography and inductively coupled plasma etching. The single or quasi-single mode propagation was observed for channel width of 0.3 - 1.0 microns and thickness of 0.32 microns at a wavelength of 1.55 microns. Propagation loss evaluated using the Fabry-Perot resonance method was of 10 inverse cm order for these channel widths. The large effective index of the guided mode over 4.5 was also observed, which well agreed with the simulation. When channel width was 0.5 microns, the bend loss of 0 - 1 dB was roughly evaluated even though the bend radius was 0.5 - 9.5 microns. The similar low loss was also confirmed for half circular disk waveguides butt-joined to use as 90-degree-bends. These results suggest the potential of an ultra-high density optical wiring in lightwave circuits.