PURPOSE: To monitor the abnormality of a light propagation path on a transmission side, by interposing an optical filter having a specific wavelength and specific reflectivity on the way of the light propagation path or the end surface thereof.
CONSTITUTION: For example, a long wavelength cutting filter reflecting a wavelength of 1.3μm and transmitting a wavelength of 0.85μm is vapor-deposited on the end surface of the optical connector connected to the light circuit terminal apparatus FSU of a subscriber's house. When the use wavelength of this system is set to 0.85μm and the maintenance wavelength thereof is set to 1.3μm, so far as a laser diode or LED of 0.85μm is used to perform transfer of signals, the effect of the filter does not appear too much. When light of 1.3μm is incident as maintenance one from a transmission side, the light of 1.3μm returns to the transmission side through an optical cable with high reflectivity by the filter on the end surface of the optical connector and the power of said light can be measured by the branch device on the transmission side. By this method, the maintenance and investigation on a trouble point up to the end surface of the final optical connector of the optical cable can be performed.
YANAGAWA HISAHARU
KAMATA YOSHIYUKI
HAYAKAWA KOICHI
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