Performance evaluation of superchannels using all-optical M-QAM OFDM and coherent receiver in the presence of time and frequency offsets

In the presence of OFDM symbol time misalignment (STM) and subcarrier frequency offset (ScFO) in an all-optical orthogonal frequency division multiplexing (AO-OFDM) system, the BER performance degraded due to intercarrier interference (ICI) and intersymbol interference. In this paper, an analytical study of the impacts of ScFO and STM on BER performance of M-QAM AO-OFDM system is conducted. The numerical results of the realistic AO-OFDM system are compared with an odd-and-even and a decorrelated emulation setups for precise estimation of STM and ScFO tolerances. For BER=10^-3, maximum acceptable relative deviations for the STM and the ScFO are 3.2% and 5.5% for the realistic AO-OFDM system. Finally, the minimum requirements of cyclic prefix (CP) are evaluated, and it is demonstrated that the STM variance is reduced by 3.3 dB at half of data rate, while the 1.8 × subcarrier spacing is required to reduce the ScFO variance by 6.9 dB.