| 摘要 |
PURPOSE:To stably judge optical input interruption. CONSTITUTION:A band filter 10 is connected to an amplifier 3 and uses one part of the occupied band (such as a low frequency area, for example) of a data signal as a passing band. A detector 11 detects the output of the band filter 10. A subtracter 12 subtracts the output of the detector 11 from the output of a detector 17, and the output of the subtracter 12 is inputted to a comparator 13. The comparator 13 judges whether the output DC signal of the subtracter 12 is higher than a level decided in advance or not, and the result is outputted to an optical input interruption alarm output terminal 16. Therefore, the optical input interruption can be stably judged at all times. |
