An Improved Envelope Tracking SOA Amplifier for CO-OFDM Transmission by Using PSO

Envelope tracking (ET) is a popular technique for improving the power efficiency and linearity of radio-frequency power amplifiers. In this paper, we investigate its use in a Coherent-Optical OFDM transmitter using a Semiconductor Optical Amplifier (SOA) as a power booster. At a fixed bias current, such amplifier may lead to significant nonlinear effects, especially when the signal to be amplified has a non-constant envelope. Thanks to a bias current control scheme, an efficient linearization of the SOA can be achieved. It is shown that the bit error rate (BER) performance of a SOA-based CO-OFDM system can be largely improved by jointly tuning significant key parameters associated with the E T block. A particle swarm optimization (PSO) is applied for identifying the best operating conditions of the ET scheme, which is eventually combined with Peak to Average Power Ratio (P APR) reduction via nonlinear companding. Three distinct scenarios are proposed depending on the tuned parameters. An improvement of up to 8 dB is achieved at a BER of 10–3, for a 5 Gb/s QAM/CO-OFDM transmission.