Micro optical circuit and optical mode converter

A micro optical circuit comprising:

• a first micro optical waveguide having a first bottom face, a first top face arranged at a first height from the first bottom face, and a first side face and a second side face substantially perpendicular to the first bottom face and the first top face;
• and
• a second micro optical waveguide having a second bottom face, a second top face arranged at a second height from the second bottom face, a third side face and a fourth side face substantially perpendicular to the second bottom face and the second top face, and a boundary face to which the first micro optical waveguide is connected, the second height being larger than the first height,
• wherein the first side face is connected to the third side face at a first connection point in a plan view.
• wherein the second side face is connected to the fourth side face at a second connection point in a plan view, and
• wherein an intersection between the boundary face and a center line equidistant from the third side face and the fourth side face is present in a region between a first straight line and a second straight line in a plan view, the first straight line passing through the first connection point and the second connection point, the second straight line crossing the second micro optical waveguide so as not to cross the first micro optical. waveguide.