Performance Analysis on the Decision-directed Equalizer in Coherent Optical OFDM

The theory model of phase noise(PN) and Chromatic Dispersion(CD) in Coherent Optical Orthogonal Frequency-Division Multiplexing(CO-OFDM) systems is theoretically analyzed and the effect of PN and CD on the constellation is also given.Based on the analysis,the principles and design of pilot-based decision-directed equalizer of CO-OFDM systems are probed in detail.Then numerical simulations on the performance of Decision-directed Equalizer(DDE) were implemented.The simulation results show that the bit error ratio(BER) performance of the DDE can always achieve 10-3 which is the commonly-reported Forward Error Correction(FEC) threshold,and this can make the following FEC module reduce the BER rapidly.Furthermore,the performance of DDE is not improved obviously when the laser linewidth is smaller than 100 kHz.Therefore,the laser with 100 kHz linewidth is recommended in CO-OFDM systems with DDE for the consideration on tradeoff between cost and BER performance.