| 摘要 |
PURPOSE:To enable the switching of transmission lines automatically even when a fault takes place in an optical transmission line and the transmission quality is not satisfied by installing two systems of the optical transmission line and a coaxial transmission line in trunk lines in a CATV optical transmission system. CONSTITUTION:A level detection circuit 13 detects a light receiving current of an O/E section 10 and a comparator circuit 14 compares the light receiving current with an optional setting value. The result is inputted to a control signal generating circuit 15, then a transmission line changeover circuit 8 in an optical transmitter 2 is controlled via a transmission line changeover circuit 11 in an optical transmitter 4 and an optional transmission means 9 based on the result of the comparator circuit 14, and when the performance of the optical transmission line is deteriorated and the transmission quality is not satisfied, it is possible to select automatically the transmission line from the optical transmission line 3 to the coaxial transmission line 5. |
