Hello shahbaz,your system is correct however you need to set 20 GHz at bessel filter and you will get the desired eye.Following things you need to be correct
You have used bessel filter for detecting 1590 nm but after that you took same value for next receiver too.you need to change that value of bessel filter to 1590.8 and so on for rest of wavelengths.why you have used fabry parrot filter at second channel on rx side?
2. You have no need to input 10 dB power as i have got ber of -50 by just putting 0 dBm input power.on the second prbs set it to script mode as there you have set 2.5 G.i think it was just a mistake
3 .moreover you do not need edfa as over 20 km link length your ber is good.if you want to use it then go for optical amo. Oprated in gain mode.you no need to change other values of amo.
4. For downstream you have used 1310 nm right? But you havnt analyzed that upstream signal any where in system .just end up after circulator.either you use time division here as given in TWDM pons.if you only use wdm pon then use different wavelengts here to and use Awg to route tjen differently.
I suggest u to go for n read discussion on forum title Twdm pon author shaid