Hi Dhanajay
In order to realize bidirectional ofdm system first you need to make a system using bidirectional fiber by placing ofdm transmitter and receiver on both sides .However working of bidirectional fiber in bidirectional system is little tricky ,you need to add null signals for upstream tx signals.Here are some examples of bidirectinal fiber and working
Lesson 5: Bidirectional Simulation — Working with Multiple Iterations
Use of BD in Bpon is given in this link
Broadband Optical System Based on a Passive Optical Network (BPON)
Try designing system by taking one Tx and Rx on both sides and if it works try to increase them.Let us know if our information helps and share your base paper or reference content you wish to reproduce for better information.
Regards