Optical device for coupling light and method for fabricating the same

An optical device, comprising:

• a waveguide,
• a grating portion, the grating portion comprising first groups of grating patterns and second groups of grating patterns, a first interval between the first groups of grating patterns is different from a second interval between the second groups of grating patterns, wherein at least one group of the grating patterns among the first and second groups of grating patterns comprise trapezoid-shaped grating patterns, and at least one group of the grating patterns among the first groups of grating patterns include step-shaped sidewalls.

A method, comprising:

• forming a dielectric layer on a semiconductor substrate;
• forming a light-guiding material layer on the dielectric layer, the light-guiding material layer comprising a waveguide and a grating coupler, the waveguide comprising an end portion, wherein the grating coupler comprises a first portion optically coupled to the end portion of the waveguide and a second portion optically coupled to the first portion, and the second portion comprises groups of grating patterns;
• filling gaps between the grating patterns with a filling element, wherein the groups of grating patterns comprise trapezoid-shaped grating patterns, and at least a portion of the gaps includes step-shaped sidewalls.