Optical coupling structure

A coupling structure for optically coupling a first optical mode having a first effective index and a second optical mode having a second effective index strictly greater than the first effective index, the coupling structure comprising:

• a first waveguide comprising a core configured to guide the first optical mode, the core extending beyond the first waveguide in an extension comprising a proximal section, close to the first waveguide, and a distal section in contact with the proximal section,
• a second waveguide comprising a base and a ridge, configured to guide the second optical mode,
• a hybrid waveguide, interposed between the first and second waveguides, comprising the proximal section and an extension of the base beyond the second waveguide, arranged to cooperate to guide an intermediate optical mode optically coupled to the first optical mode by the extension, and
• a modal transition section extending from the hybrid waveguide to the second waveguide, comprising the distal section;
• wherein the coupling structure is such that:
• the proximal section has a width at a junction with the distal section such that an effective index of the intermediate optical mode is strictly greater than the second effective index, and
• the distal section continuously narrows away from the hybrid waveguide so as to perform optical coupling between the intermediate optical mode and the second optical mode.