An optical element according to the invention uses a thin film-like two-dimensional
photonic crystal having a structure of periodic repetition in two directions perpendicular
to each other. When the two periodic directions are Y-axis and Z-axis directions,
opposite surfaces of the photonic crystal structure perpendicular to the Z-axis
direction and parallel to the Y-axis direction are used as a light input surface
and a light output surface respectively. The direction of movement of light rays
incident onto the light input surface is decided so that it is parallel to the
YZ plane and inclined at a predetermined inclination angle to the Z-axis direction.
