High efficiency grating coupler between silicon-on-insulator waveguides and perfectly vertical optical fibers.

A high-efficiency waveguide-to-fiber grating coupler for silicon-on-insulator waveguides was designed. Perfectly vertical fiber coupling is achieved by using an asymmetric grating structure to suppress the second-order Bragg reflection from the grating. The ability to use a perfectly vertical positioned optical fiber simplifies the packaging of the photonic integrated circuit. A coupling efficiency of 80% at a wavelength of 1.55 microm is obtained.