| 摘要 |
PURPOSE:To accurately detect a state of a faulty transmission line by differentiating a carrier frequency applying analog modulation to an optical signal at a sender side from both stations in the optical transmission system in which a digital information signal and an auxiliary data signal obtained through analog modulation of the digital information signal are sent. CONSTITUTION:An electric signal A sent from its own station 1 is subject to PAM modulation at an analog modulation circuit 8 by using an auxiliary data signal and converted into an optical signal A' by an electrooptic conversion circuit 4 and sent to an optical transmission line 3 through an optical directional coupler 6. On the other hand, an optical signal B' from an opposite station B is inputted to an optoelectric conversion circuit 5 through the optical directional coupler 6, converted into an electric signal B and outputted. A carrier signal separated by the signal B from an auxiliary data signal band pass filter 12 is detected by a signal interrupt detection circuit 13. When the optical transmission line 3 is broken, the optical signal A' sent from its own station 1 is reflected at a broken point 11 and returned and since the center frequency sent from its own station 1 and the pass frequency of the band pass filter 12 are different, the auxiliary data signal of the signal reflected and returned does not pass the filter 12 and the signal interrupt detection circuit 13 discriminates it as a fault of a transmission line. |
