Optical fiber composite overhead ground wire (OPGW), which is used as communication lines by electric power companies, sometimes freezes and causes communication faults in winter season because of rainwater immersion into aluminum pipes which envelop optical fibers (referred to as OP unit). The rainwater in OP unit causes corrosion reaction with aluminum, and generates hydrogen gas. If the hydrogen gas penetrates the core of an optical fiber, optical loss at the wavelength of 1.24 and 1.625 µm increases. The author proposes an estimation method of water immersion amount in OP unit, based on continuous measurement data of an optical time domain reflectometer (OTDR) using 1.24/1.625 µm.
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