On envelope-tracking for SOA amplification of multicarrier signals

Semiconductor Optical Amplifiers are known to be prone to nonlinear effects in the saturated regime. This is particularly true if the signals to be amplified have a non-constant envelope and a high Peak-to-Average Power Ratio (PAPR). The benefits of envelope-tracking is investigated here for linearizing a Coherent-Optical OFDM (CO-OFDM) transmitter employing a SOA as a power booster. The effect of a filtered envelope is studied and its optimum amplification gain is evaluated by considering an accurate physical model of the SOA. Moreover, the joint combining of PAPR reduction (via nonlinear companding) and envelope tracking is proved to be effective, with a power margin close to 5 dB.