Hi Yasir
If your design requirement is 800 ONUs.I suggest you to use a TWDM or OFDM PON architecture.WDM Provides a point to point link between the transmitter and reciever but implementing that for such a great number requires a vast infrastructure.TDM on the other hand provides a point to multipoint link.The hybrid combination of the two will help you to design a system with large ONU capacity.
Hope it solves your problem.
Regards