| 摘要 |
PURPOSE:To surely receive an information signal by correcting an incident luminous quantity of a light receiving element with an optical attenuator, correcting the light receiving sensitivity of the light receiving element and selecting a gain of an amplifier circuit so as to correct a level of an output signal. CONSTITUTION:An optical attenuation means 26 attenuates the luminous quantity of a received optical beam L2 made incident in a light receiving element 16 based on the result of detection of the luminous quantity to correct the luminous quantity of the received optical beam L2 made incident in the light receiving element 16 and also to control the light receiving sensitivity of the light receiving element 16 and to correct a level of an output signal. Even when the incident luminous quantity of the received optical beam L2 is largely changed, it is possible to keep the level of the received optical output signal to be a prescribed level. In this case, an avalanche photodiode is adopted for the light receiving element 16 and the light receiving sensitivity of the light receiving element 16 is largely changed by controlling a multiple factor M of the avalanche photodiode 16, and the light receiving sensitivity of the light receiving element 16 is controlled based on a gain control voltage of an AGC circuit 38. |
