SEMICONDUCTOR LIGHT RECEIVING DEVICE

PURPOSE:To improve S/N of a light receiving device which converts a weak optical signal photoelectrically, by superposing the steady signal light of a required level onto the optical signal from an optical fiber transmission light to receive the light. CONSTITUTION:One end of an optical fiber 22 for transmission of a steady signal light is provided adjacently to a fiber end 21 of an optical fiber transmission line 1, and a luminous source 23 and an output control power source 24 for this luminous source 23 are provided at the other end of the fiber 22. A condenser lens 25 is provided between ends of fibers 1 and 22 and a light receiving element 2, and the light flux of the optical signal from fibers 1 and 22 is condensed and incident to the element 2. Since the steady signal light of a required level from the luminous source 23 is superposed to the weak optical signal from the fiber 1 and the optical signal of an optimum receiving light level is received by the element 2, S/N for shot noise and heat noise is improved when the optical signal is converted to an electric signal and is amplified in a circuit 4.