Noise spread mitigation in optical DFT-S OFDM systems based on in-band RF pilot-tone

In the optical DFT-S OFDM system, noise spread induced by inverse discrete Fourier transform at the receiver, is proved to reduce the optical signal-to-noise ratio (OSNR). It features noise spread over the whole DFT-S OFDM subband. This paper firstly explores the noise spread mitigation method in DFT-S OFDM systems. A 400 Gb/s multiband 16QAM DFT-S OFDM system based on in-band RF pilot-tone was performed under different transmission conditions. The results show that in-band RF pilot-tone could improve the tolerance of systems to laser linewidth and launch power into fiber. Compared to the conventional subcarrier-pilot-based scheme, OSNR reduction of 0.6 dB and 1 dB for BTB and 240 km fiber transmission respectively at the BER of 3.8×10−3 shows that the RF pilot-tone based method is a feasible way for noise spread mitigation.