Demonstration of Symmetrical 25 Gb/s TDM-PON With Multilevel Interleaving of Users

A cost effective symmetrical 25 Gb/s TDM-PON utilizing a novel multilevel user-interleaving scheme based on PAM-4 in the downstream and three-level duobinary modulation in the upstream is demonstrated without using any DSP. At the ONU, we used a commercial off-the-shelf 10 Gb/s EML-based transmitter and a 10 Gb/s APD/TIA-based receiver to keep the cost low. It will be shown that three-level duobinary and PAM-4 modulation are more tolerant to chromatic dispersion compared to NRZ; therefore, it also offers a reach extension. The multilevel user-interleaving scheme enables the use of a half-rate CDR at the ONU as well as the use of a simple NRZ CDR/EDC to improve the optical receiver sensitivity for downstream transmission. We believe that using PAM-4 modulation for the downstream and NRZ to duobinary conversion for the upstream offers a good technical compromise for lowest cost at the ONU for 25 Gb/s TDM-PON.