Narrowband silicon waveguide Bragg reflector achieved by highly ordered graphene oxide gratings.

Graphene oxide (GO) ultrathin film can be wafer-scale deposited by spin coating, can be patterned by laser interference lithography and oxygen plasma etching, can be thinned atomically (0.26 nm/min) and oxidized by ozone treatment, and is a relatively transparent and low-refractive-index material compared to pristine graphene. All those unique properties prompt us to realize a low-loss (∼5  dB/cm), high-extinction-ratio (19 dB), and narrowband (0.425 nm) GO/silicon hybrid waveguide Bragg reflector by transferring 7-nm-thick GO gratings (n=1.58) atop a silicon strip waveguide. Unlike a sidewall-corrugated strip waveguide Bragg reflector that generally exhibits distorted corrugation profiles and is sensitive to fabrication errors, the as-realized GO-grating-covered strip waveguide Bragg reflector exhibits a stable reflecting wavelength and controllable reflection bandwidth that can be well predicted by numerical simulations.