| 摘要 |
PURPOSE:To allow an avalanche photodiode (APD) to operate constantly with a certain high sensitivity independently from temperature variations, by utilizing the self-bias method with a combination of a differential amplifier and a light- emitting diode. CONSTITUTION:Signal light 1 is collected by an optical system to the light receiving surface 3 of an APD2. A light emitting diode 4 is disposed at a position where it does not obstruct the signal light 1, the diode having emission spectrum in the wave range where the APD has sufficient spectral sensitivity. This diode is caused to emit light by an output from a differential amplifier 5 for amplifying the difference in potential across a bias resistance 7, whereby bias light 6 is applied to the APD light receiving surface. To the APD2, a bias voltage is applied from a bias power source 9 which has a voltage larger than the maximum breakdown voltage in a range of environmental temperatures used, through the bias resistance 7 and the output resistance 8. An output signal 11, which has been photoelectrically converted, is taken out from the APD through a coupling capacitor 10. |
