When a guide groove for a lens is formed in a single crystal silicon substrate,
a rectangular parallelepiped opening is formed having a width smaller than a desired
width of the guide groove and is then processed by wet etching using a KOH solution.
Two {111} planes are exposed on at least one end surface of the guide groove in
an optical axis direction, and the planes described above are inclined toward the
substrate side from the upper and the lower sides. Since a protrusion portion protruding
to the guide groove side is not provided at the bottom part of the end surface,
a light-emitting diode and a lens can be disposed close to each other, thereby
forming an optical coupling device having high optical coupling efficiency obtained
between elements.
