Waveguide-coupled drop filters on SOI using quarter-wave shifted sidewalled grating resonators.

We report on the design, fabrication, and demonstration of waveguide coupled channel drop filters at 1550 nm, on a silicon-on-insulator (SOI) substrate. These devices rely on resonant power transfer from a bus waveguide to side-walled Bragg resonators with quarter-wave shifts in the middle. By employing a second mirror resonator, and a tap-off waveguide, reflections along the bus waveguide can be reduced, leading to realization of circulator-free resonance filters. These devices were fabricated on SOI using e-beam lithography and inductively coupled plasma (ICP) etching. Fabricated devices with two coupled cavities are demonstrated to have rejection ratios greater than 20 dB and 3-dB bandwidths of 110 GHz, close to the values predicted by numerical modeling. We also demonstrate power tap-off at resonance of around 16 dB.