Bit-error-rate degradation due to on-line OTDR monitoring above 1.6 μm

1625/1650 nm optical time-domain reflectometers (OTDRs) are commercially available and are used for on-line monitoring of fibers carrying signals in the 1550-nm window. Because OTDRs operate with high peak powers stimulated Raman scattering (SRS) will deplete the signal in the 1550-nm window. We have considered OTDR pulses that are copropagating with the signal. If the OTDR pulses are counter-propagating the system degradation is reduced significantly. However, this solution restricts the use ofan OTDR in a network node to monitoring fibers with incoming traffic. The OTDR-introduced penalty can alternatively be reduced by choosing a wavelength closer to the signal window or by decreasing the peak power or duty cycle of the OTDR pulses