| 摘要 |
PURPOSE:To detect deterioration in optical output waveform by differentiating a monitoring signal converting an optical output signal into an electric signal, detecting the pulse width of a differentiating circuit output pulse and sending an alarming signal when the pulse width reaches a prescribed value or above. CONSTITUTION:A transmission signal 11 is converted into an LD driving signal 12 by a driving circuit 1 and subjected to electrooptical conversion by an LD 3 and the result is sent to a transmission line using an optical fiber as an optical output signal 13 and the optical output signal 13 is subjected to photoelectric conversion by a monitoring photodiode 4 in the LD module 2 into a monitoring signal 14. The monitoring signal 14 is differentiated by a differentiation circuit 5 and converted into a differentiation output pulse signal 15. A pulse width detecting circuit 6 detects the pulse width of the differentiation output 15 and sends an alarming signal 16 when the pulse width reaches a prescribed value. Thus, the deterioration in the optical output waveform is directly detected. |
