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 equip- ment on the subscriber side. This method employs a 13/1.55- pm-WDM dichroic reflective optical filter and a 1.55-pm-band 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-pm-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 is fabricated and which achieves the target characteristics and reliability. System eval- uation experiments are carried out and the possibility of 100% fault identification is confirmed as a result of accuracy tests in the field.