Distortion and regeneration of optical 32QAM by semiconductor optical amplifiers

Numerical results for distortion and further regeneration of optical 32QAM by SOAs are presented. The distortions caused by the first SOA were reduced by a second device acting as a saturable absorber. EVM is reduced from 36% to 16% for 10 Gbaud, and from 24% to 12% for 20 Gbaud (Pin = -10.5 dBm). It is demonstrated that the two SOAs, if properly operated, can work as a quasi-linear amplifier and so be eligible to be used in middle range links employing multilevel and/or phase encoded optical signal.