Agree with alistu.may i know you are working on optisystem sample file? Or you have realized or reproduce any paper.share your simulation and paper for better under standing.Now i have some doubts,since you mentioned wdm pon then how would wdm pon possible without multiplexing of different wavelengths? You need to use wdm mux.Demux also required at reception to get different or specific wavelength .eye looks fine in terms of q factor and ber but hard to state wether this is of required single wavelengh or mixed signal if you havnt used demux.otherwize effects of crosstalk are there as alistu defined beautifully