| 摘要 |
PURPOSE:To eliminate an influence on a main signal system and to accurately detect optical input interruption even if the fault of a circuit occurs by providing a clad light detection means detecting the propagation light of the part of the an optical fiber, discriminating a detection signal level and detecting optical input interruption. CONSTITUTION:For an optical input from the core part of the optical fiber 1, data output is generated through a photoelectric conversion element 2, an equivalent amplifier circuit 3, a discrimination circuit 5. On the other hand, the propagation light of the clad part of the optical fiber 1 is inputted to the photoelectric conversion element 7, and the electrical signal output of the photoelectric conversion element 7 is added to a comparator 6 and compared with a reference value. When the output level of the photoelectric conversion element 7 is below the reference value, the comparator 6 generates an output showing optical input interruption. Thus, optical input interruption can accurately be detected without affecting the main signal light which is propagated through the core part and even if the fault of the circuit occurs. |
