CoherentopticalOFDM(CO-OFDM)hasrecentlybeenproposedandtheproof-of-concepttransmissionexperimentshaveshownitsextremerobustnessagainstchromaticdispersionandpolarizationmodedispersion.Inthispaper,wefirstreviewthetheoreticalfundamentalsforCO-OFDManditschannelmodelina2x2MIMO-OFDMrepresentation.