- We study the performances of several electrical dispersion compensation (EDC) equalizers in the presence of chromatic dispersion (CD) and polarisation mode dispersion (PMD) for optical coherent detection OOK system. The EDCs that are analyzed include decision feedback equalizer (DFE), linear equalizer (LE), and maximum likelihood sequence estimator (MLSE). We present an inclusive quantitative analysis of the performance difference between the various techniques. The MLSE gives a good indication of the best possible performance. We also present the performances of the same EDCs for direct detection OOK system. It is shown that in coherent detection the performances of both the DFE and LE are effectively the same, whereas in direct detection the DFE is preferable.