Long-reach single-mode-fibre OTDR using a 1.5 μm semiconductor laser

We report an OTDR operating at 1.535 μm wavelength, capable of fault location over 100 km of commercial single-mode fibre. Whereas the one-way loss range of an OTDR is conventionally quoted for a received signal/noise ratio of unity, we demonstrate that a margin of at least 3 dB should be allowed in deducing the realistic range of fibre loss over which faults could be located.