Loss Cause Identification by Evaluating Backscattered Modal Loss Ratio Obtained With 1-μm-Band Mode-Detection OTDR

We propose a novel diagnostic technique that uses 1-μm-band mode-detection optical time domain reflectometry (1 μm-OTDR) to identify the loss causes such as macrobends and fusion splices, of single-mode fibers. 1 μm-OTDR, which employs 1-μm-band probe pulses and a mode selective coupler operating in the same band, enables us to individually observe the fundamental (LP
₀₁
) and the second-order (LP
₁₁
) modes of the backscattered light generated in the two-mode region of single-mode fibers. Evaluating the ratio of losses occurring in the LP
₀₁
to LP
₁₁
modes of the backscattered light allows us to determine whether the cause of loss is a macrobend or a fusion splice. A proof-of-concept demonstration is performed for two kinds of widely used single-mode fibers, and the results show that macrobending and fusion splice losses can be clearly identified.