Impact of multiple reflection noise in Gbit/s lightwave systems with optical fibre amplifiers

Severe systems degradations and bit error ratio floors are observed in high-speed (11 Gbit/s) lightwave transmission systems with optical amplifiers due to multiple reflections which convert laser phase noise into intensity noise. This effect is greatly intensified due to the amplifier gain and also because of the additional presence of single-spontaneous emission beat noise. Furthermore, even if discrete reflections in the fibre transmission path are eliminated, the multiple reflection noise arising from Rayleigh backscattering ultimately limits the maximum useful gain for optical repeaters to a level far below the maximum allowable gain to avoid lasing, unless optical isolators are employed.