Low-distortion inline amplification of single-channel 16/64QAM signals using SOAs with optimized holding beam

Semiconductor optical amplifiers (SOAs) are typically not recommended for amplification of coherent signals due the gain and phase distortions introduced by them. However, in the presence of a saturating holding beam (HB), these distortions can be minimised, with a trade off in the achievable gain. In this paper, we present a detailed experimental analysis of identifying the HB parameters for 16 and 64QAM signals to maximise the signal gain while minimising the bit error rate (BER) at different input optical signal to noise ratios (OSNRs). With optimised holding beam parameters, we demonstrate an improvement in Q factor by 4 dB and 2 dB respectively for 16 and 64QAM signals with a reduction of corresponding signal gains by only 4 dB and 6 dB respectively. We demonstrate the efficacy of the approach for polarization multiplexed signals as well. All these results prove the potential of using SOAs as inline amplifiers, especially for amplification outside the C-band.