Decentering optical system, optical transmitting device, optical receiving device, and optical system

A decentering optical system which takes a substantially parallel beam as input light, comprising a prism whose refractive index is greater than 1, wherein:

• at the boundary surface of the prism, at least five optical surfaces, which are arranged so as to be mutually decentering or inclined, are formed, in order along one optical path in which the input light pursues, as a first surface, a second surface, a third surface, a fourth surface, and a fifth surface;
• at least one among the five optical surfaces is a splitting surface which splits the optical path of the input light into a transmission optical path and a reflection optical path;
• the reflection optical path is an optical path along which the input light proceeds in order from the first surface to the fifth surface and is emitted to the exterior of the prism;
• and
• at least one real image is formed within the prism upon the reflection optical path or upon the transmission optical path.