Performance Analysis of Direct Detection and Coherent Detection Optical-Orthogonal Frequency Division Multiplexing Systems

We investigate the complex interaction between direct detection and coherent detection optical-OFDM systems at 10 Gb/s and 4-QAM. We show how fibre dispersion causes different quadrature amplitude modulation (QAM) constellation phase rotations as a function of OFDM sideband frequency. We investigated that in case of DDO-OFDM we need to extend constellation amplitude up-to 2m whereas in CDO-OFDM it is limited to 1m. In case of DDO-OFDM double side band is produced which makes lot of bandwidth wastage. We also investigate that Carrier boosting at the receiver enables direct detection optical OFDM (DDO-OFDM) to outperform coherent OOFDM in the nonlinear limit.