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

A method of fabricating a spot size converter comprising:

• providing a substrate;
• forming an optical waveguide having at least one core layer and at least a first cladding layer and a second cladding layer such that
• the first cladding layer is located between the substrate and the core layer and the second cladding layer is arranged on a side of the core layer facing away from the first cladding layer,
• the core layer has a first thickness in a first section of the spot size converter, and
• the core layer in a second section of the spot size converter has a second thickness which is smaller than the first thickness;
• forming a ramp region located between the first and the second section and in which the thickness of the core layer decreases continuously,
• forming a facet via which light can be coupled into an optical device, wherein
• forming a guiding structure in the core layer, the guiding structure configured to guide light laterally, wherein the guiding structure does not extend to the facet, and wherein
• the core layer comprises lithium niobate or silicon nitride.