Time and frequency synchronisation in all-optical orthogonal frequency division multiplexing systems

In all-optical orthogonal frequency division multiplexing (AO-OFDM) systems, symbol time misalignment (STM) and subcarrier frequency offset (ScFO) result in intercarrier-interference and intersymbol interference, leading to degradation of bit error rate (BER) performance. In this study, an analytical study of the impacts of STM and ScFO on AO-OFDM system performance is conducted. In the presence of STM and ScFO, AO-OFDM system performance is evaluated with the number of subcarriers (N_SC), cyclic prefix requirements and receiver bandwidth (BW_RX). For AO-OFDM system without CP, results show that the STM gives higher BER than the ScFO. To keep the BER below 10^-3 in AO-OFDM systems with on-off keying-modulated three optical subcarriers and homodyne detection with BW_RX = 30 GHz, the maximum acceptable relative deviations for the STM and the ScFO are 11 and 14%, respectively.