Optical coupler and optical device including the same

An optical coupler comprising:

• a substrate;
• a buffer layer on the substrate;
• and
• an optical coupling layer including a horizontal mode expander layer and a vertical mode expander layer,
• wherein the horizontal mode expander layer expands in one direction on the buffer layer, and
• wherein the vertical mode expander layer adjusts a stepped difference between the horizontal mode expander layer and a plurality of optical transmission devices having different diameters or cross-sectional areas and connected to first and second sides of the horizontal mode expander layer, and the vertical mode expander layer is disposed on a side of the horizontal mode expander layer to minimize optical loss between the plurality of optical transmission devices, and
• wherein the horizontal mode expander layer of the optical coupling layer comprises:
• a waveguide coupling region disposed on the first side of the vertical mode expander layer and having a first width that is greater than a width of one of the plurality of optical transmission devices;
• a horizontal expander region connected to the waveguide coupling region and having a first divergence width that gradually increases in a direction away from the waveguide coupling region;
• and
• a vertical expander region connected to the horizontal expander region and having a second width that is same as a width of another one of the plurality of optical transmission devices,
• wherein the second width is greater than the first width.