| 摘要 |
PURPOSE:To detect a fault of an optical transmission line independently of the number of branches by providing an interference film filter to each terminal equipment in the distribution type optical transmission system, sending an optical signal from a center while varying the wavelength and detecting a level of a returned light. CONSTITUTION:A center 1 is connected to terminal equipments 21-2n through an optical fiber 6 and optical distributers (T) 71-7n and an interference film filter 8 with different wavelength characteristic is provided respectively to the terminal equipments 21-2n. When an optical signal is sent to a transmission line being an optical fiber 6 through an optical directional coupler 5 from a variable wavelength light source (OSC) 3 of the center 1, the optical signal is made incident in the terminal equipments 21-2n and only the optical signal with a specific wavelength is much reflected by the interference film filter 8 and returns to the center 1. Thus, the returned optical signal is detected by a photodetector (DET) 4 through the optical directional coupler 5. If the optical fiber 6 is broken at the branched destination, since only the level of the reflected light of the wavelength is lowered, the fault of the transmission line is detected. |
