| 摘要 |
PURPOSE:To surely detect the interruption of an optical input signal, by providing the 2nd ADP having the same dark current characteristics as an avalache photodiode receiving the optical signal and interrupting an optical input. CONSTITUTION:An optical reception system is provided with the 1st ADP1 receiving an optical input and the 2nd APD2 interrupting the optical input with a cap or the like, and the same reverse bias voltage VB is applied to both of them. In case of optical input signal interruption, the amplification factor of the APDs is increased by the automatic gain adjusting function and a peak value of the shot noise due to the dark current of the APDs stable at a prescribed level, then a dark current ID is very large at the increased reverse bias voltage VB. This dark current ID is detected as a voltage drop of a resistor R3 in series connection with the ADP2, and when the said voltage drop is a threshold voltage Vth or more, input signal interrupting detection information SD is outputted from a comparator COMP. |
