| 摘要 |
PURPOSE:To test an operation of a monitoring circuit by on-line, by forcibly making an excessive current flow to the monitoring circuit of a light emission element, which is used for an optical transmission device. CONSTITUTION:A digital input signal passes through a waveform processing circuit 2 from an input terminal 1, a part of which is applied to a driving circuit 3, drives a laser diode 4 and outputs an optical signal 16. A part of the optical signal 16 is converted to an electrical signal by a photodetecting element 14, is applied to a voltage comparing circuit 11 through an amplifier 13 and a mean value detecting circuit 12, and is compared with reference voltage which is obtained through the waveform processing circuit 2 and a means value detecting circuit 15. In this case, when the laser diode is deteriorated and the optical output is decreased, a bias current of the laser diode 4 is increased by controlling a current source 10, and an alarm is raised by an alarming circuit 9 by monitoring said bias current by a monitoring cir- cuit 8, but when executing a test, a switch 7 of a shunting circuit 5 is closed, the bias current is increased forcibly, and the monitoring circuit 8 is operated. |
