Spot-size converter, photonic device and method for fabricating spot-size converter

A photonic device, comprising a spot-size converter, wherein the spot-size converter is provided with a first end face for coupling to an integrated optical waveguide and a second end face for coupling to an optical fiber, wherein the second end face is parallel to the first end face, the spot-size converter comprising:

• a substrate, provided with a first recess that is exposed to its top surface and the second end face;
• an isolation layer, located on the substrate and provided with a second recess and a third recess that are exposed to a top surface of the isolation layer and the second end face, the second recess being provided with a plurality of first holes communicating with the first recess, the third recess being provided with a plurality of second holes communicating with the first recess, and a portion of the isolation layer located between the second recess and the third recess forming a first transmission portion that extends to the second end face in a first direction, wherein the first direction is orthogonal to the first end face and the second end face;
• a waveguide layer, located on the isolation layer, a dimension of the waveguide layer in a second direction decreasing in a direction approaching the second end face, and the waveguide layer comprising a portion that protrudes in the form of a ridge from a surface of the first transmission portion, wherein the second direction is orthogonal to the first direction and parallel to a bottom surface of the substrate;
• and
• a cover layer, located on the waveguide layer and covering the waveguide layer, the cover layer comprising a second transmission portion located on the surface of the first transmission portion and extending to the second end face in the first direction.

A method for fabricating a spot-size converter, the spot-size converter being provided with a first end face for coupling to an integrated optical waveguide and a second end face for coupling to an optical fiber, wherein the second end face is parallel to the first end face, the method comprising:

• forming an isolation film layer on a substrate base;
• forming a waveguide layer on the isolation film layer, a dimension of the waveguide layer in a second direction decreasing in a direction approaching the second end face, wherein the second direction is parallel to the first end face and the second end face and parallel to a bottom surface of the substrate base;
• forming a cover film layer on the isolation film layer and the waveguide layer;
• etching the cover film layer and the isolation film layer to form structures of a cover layer and an isolation layer, wherein the isolation layer is provided with a second recess and a third recess that are exposed to its top surface and the second end face, wherein a plurality of first holes are provided at a bottom of the second recess, and a plurality of second holes are provided at a bottom of the third recess, and wherein a portion of the isolation layer located between the second recess and the third recess forms a first transmission portion that extends to the second end face in a first direction, and the cover layer covers the waveguide layer and comprises a second transmission portion located on a surface of the first transmission portion and extending to the second end face in the first direction, the first direction being orthogonal to the first end face and the second end face;
• and
• etching the substrate base through the plurality of first holes and the plurality of second holes to form a structure of a substrate, wherein the substrate is provided with a first recess that is exposed to its top surface and the second end face, wherein the second recess communicates with the first recess through the plurality of first holes, and the third recess communicates with the first recess through the plurality of second holes.