A new fault-identification method using a dichroic reflective optical filter in optical subscriber loops

A new method is studied which can automatically identify faults between an optical line and the transmission equipment on the subscriber side. This method employs a 1.3/1.55-μm-WDM dichroic reflective optical filter and a 1.55-μm-band optical time-domain reflectometer (OTDR). The filter is inserted between the optical line and the transmission equipment. The level and distance of reflection from the filter are measured with a 1.55-μm-band OTDR from the central office in this fault identification method. The required characteristics and structural design method for the filter are discussed. A prototype of the filter achieves the target characteristics and reliability. System evaluation experiments were carried out, and the possibility of 100% fault identification was confirmed as a result of accuracy tests in the field