Reflection-Induced Penalty in Raman Amplifiers

We describe the measurement of reflection-induced penalties in Raman amplifier systems. We find that the reflection-induced in-band crosstalk power ratio (R sub c) provides a convenient means for predicting system penalties from crosstalk due to either a pair of discrete reflectances or a discrete reflectance combined with Rayleigh backscattering, occurring under a variety of system parameters, such as fiber attenuation, Raman gain efficiency, mode field size, connector reflectance, and fiber length. A 1-dB penalty in our optically preamplified receiver is observed when the reflection-induced in-band crosstalk level is -25.2 dB for non-return-to-zero signals and -22.8 dB for 50% return-to-zero signals. We also estimate the penalties of multi-span systems using R sub c per span. We find, for instance, that a Raman amplified system could accommodate 30 spans for an R sub c of -40 dB per span to provide a 1-dB penalty using non-return-to-zero signals.