PURPOSE: To make it possible to execute the search for a fault point readily by arranging a dielectric multilayered-film filter at the specified position of the intersections of all split paths of a light splitting/coupling device or all optical fiber lines.
CONSTITUTION: The wavelength region of passable inspecting light is limited in correspondence with the film thickness of a dielectric multilayered-film filter, which is inserted into an optical splitting/coupling device 15, in the light propagating direction at each split light port. At each split light port, several kinds of cutoff wavelengths are determined. Therefore, when a plurality of optical lines 16 are monitored based on the inspecting light emitted from a variable wavelength light source 11, each reflected light is received with a photodetector 13 for every wavelength, which is marked off with N kinds of cutoff wavelengths. Therefore, when the linear-shape operation is performed for the reflection loss of each wavelength with an operation/control circuit part 14 based on the intensity level of the reflected light corresponding to the respective wavelength, the fault point in each split light port and the line 16, which is optically connected 5, to the port, can be independently detected based on the difference of the reflected lights between the respective split light ports.
UEKI TAKESHI
SHIMIZU TAKEO
YANAGAWA HISAHARU
YAMAMOTO FUMIHIKO
NIPPON TELEGRAPH & TELEPHONE
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