Hi Aabid,
There are no examples of TWDM PON in OptiSystem samples as far as I am concerned. However, I addressed a page last week where Gulkaran was able to find the TWDM files and make the necessary changes. I also attached some screen shots with the help of which Gulkaran is able to implement downlink and uplink separately.
It should be noted that the most of TWDM files attached in the fourms may not work fine, but they can be useful to researchers to start their work with.
Regards