Spot size converter for adapting the diameter and/or the shape of a mode field of an optical component and method of fabricating a spot size converter

The invention relates to a spot size converter for adapting the diameter and/or the shape of a mode field of an optical component, comprising a substrate (10); an optical waveguide (3) comprising at least one core layer (31) and at least a first and a second cladding layer (32, 33), wherein the first cladding layer (32) is located between the substrate (10) and the core layer (31), while the second cladding layer (33) is arranged on a side of the core layer (31) facing away from the first cladding layer (32); a first section (100) in which the core layer (31) has a first thickness; and a second section (200) in which the core layer (31) has a second thickness which is smaller than the first thickness. According to the invention, a ramp region (400) is located between the first and the second section (100, 200) and in which the thickness of the core layer (31) decreases continuously. The invention also relates to a method of fabricating a spot size converter.