Optical element and optical device

A light receiving optical element made of a material transparent to light, the optical element comprising:

• a front surface having a first surface, a second surface and a third surface;
• a back surface facing the front surface;
• and
• a fourth surface connecting to the third surface,
• wherein the front surface includes a recessed surface in a region facing the fourth surface,
• the recessed surface includes the second surface and the third surface,
• the recessed surface has a point closest to the fourth surface as a closest point, and has a first singular point being a discontinuous slope point other than the closest point,
• the second surface is situated between the first surface and the third surface,
• the first singular point is a boundary point between the second surface and the third surface,
• the back surface has a fifth surface and a sixth surface,
• a second singular point being a discontinuous slope point is included in the back surface,
• the second singular point is a boundary point between the fifth surface and the sixth surface,
• the fifth surface is connected to the front surface, and
• the sixth surface is situated on the side of the fourth surface,
• wherein rays are incident from the first surface,
• the rays being incident from the first surface are reflected on the fifth surface and the sixth surface,
• the rays being reflected on the fifth surface are reflected on the second surface,
• a portion of the rays being reflected on the second surface are reflected on the third surface,
• a portion of the rays being reflected on the second surface are introduced into the fourth surface,
• the rays being reflected on the sixth surface are reflected on the third surface, and
• the rays being reflected on the third surface are introduced into the fourth surface.