An optical waveguide includes a partial cylindrical portion, and a
plurality of end portions. The partial cylindrical portion has an
elongated profile, and is formed of a material transparent to light
propagating along the partial cylindrical portion. The end portion has an
approximately partial spherical profile, smoothly joins the partial
cylindrical portion, and is formed of the same material as the material of
the partial cylindrical portion, so that the light propagates along the
partial cylindrical portion and the end portions while repeating total
reflections at a boundary surface contouring the partial cylindrical
portion and the end portions.
