| 摘要 |
PURPOSE: To surely prevent transmission of an output light toward a downstream side of an optical transmission line by detecting a fault in a modulation light from an external modulator and a fault of a drive signal for the external modulator. CONSTITUTION: An automatic output stabilizing circuit 4 receives a backward optical monitor signal of a light receiving element 1b to control automatically an output light from a semiconductor laser 1a to be at a prescribed level. An external modulator 2 receives an output light of the semiconductor laser 1a and modulates it in response to a drive signal from a modulator drive circuit 5. A light receiving element circuit 6 receives the modulated light branched by a photocoupler 3 and provides a fault detection signal on the occurrence of a fault. Furthermore, A drive signal monitor circuit 10 monitors the drive signal of the external modulator 2 and provides ah output of a fault detection signal on the occurrence of a fault. An OR circuit 11 ORs the fault detection signal from the light receiving element circuit 6 and the fault detection signal from the drive signal monitor circuit 10 and a shut-down circuit 8 receives the fault detection signal to provide an output of an optical interruption signal of the semiconductor laser 1a to the automatic output stabilizing circuit 4. |
