PURPOSE: To input a large luminous flux of the GaAs light emission diode into the optical fiber with high efficiency, by providing the GaAs light emission diode having a hemispherical lens consisting of GaAs, on the focus of the rotary parabolic reflector, providing the convex lens whose optical axis has been made to coincide with the opening of the reflector, and providing one end of the optical fiber on the focus.

CONSTITUTION: The light emission part center A of the GaAs light emission diode 3 equipped with a hemispherical lens 5 consisting of GaAs is provided to the focus of the rotary parabolic reflector 10 to which chrome plating has been performed. The convex lens 13 is provided by making its optical axis coincide with the opening 12 of the reflector 10. The arrangement is made so that the core end 9 of te optical fiber 8 conforms with said focus. The photocoupling factor of approximately 50% can be obtained by said arrangement. Accordingly, it is possible to obtain a photocoupler by which a large luminous flux from the GaAs light emission diode 3 can be input to the optical fiber 8 with high coupling efficiency.