Experimental OFDM transmission performance analysis in a SOA - fiber cavity laser

In this article, we present an experimental study of OFDM transmission using a specific bi-directional fiber cavity laser based on a semiconductor optical amplifier. We show that in the presence of sinusoidal modulation, its frequency response presents resonances relative to the optical cavity modes. We investigate first the performance of the system in terms of Error Vector Magnitude (EVM) for different configurations relative to the frequency position of the OFDM sub-carriers with respect to the frequency interval of the resonant modes. The obtained results show a significant improvement in the OFDM transmission EVM by increasing the OFDM subcarriers per frequency interval. We then analyze the impact of inter-symbol interference and inter-frame interference on the system's performance due to the round-trip echo and propose a pre-compensation method that added a small percentage of the previous symbol inversed before transmitting it inside the cavity where a decrease in the EVM is obtained respectively from 21.4% to 9.6% and from 26.8% to 13.2% for 4-QAM and 16-QAM data transmission.