| 摘要 |
PURPOSE:To easily detect a fault of an optical transmission line without error by providing an interference film filter to one end of an optical transmission line, sending an optical signal from other end and varying its wavelength so as to detect the level of the returned light. CONSTITUTION:A variable wavelength light source (OSC) 3, a photodetector (DET) 5 and an optical directional coupler 4 are connected to one end 1 of an optical transmission line being an optical fiber and the other end 2 connects to an interference film filter 6 and an optical transmitter (transmitter-receiver) 7. Then when an optical signal is outputted from a variable wavelength light source 3, the optical signal is sent to an optical transmission line 8 through the optical directional coupler 4 and the optical signal through the optical transmission line 8 enters one end 2, is radiated to the interference film filter 6 and the light with a wavelength not passing through the filter 6 is reflected in the optical transmission line 8 and returns to one end 1. The returned optical signal is branched by the optical directional coupler 4 and made incident in the photodetector 5. Thus, if no fault exists in the optical transmission line 8, the output level of the photodetector 5 is changed by varying the wavelength of the variable wavelength light source 3. |
