Reflection-induced penalty in Raman amplified systems

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