A Smooth Evolution to Next Generation PON Based on Pulse Position Modulation (PPM)

A smooth evolution of passive optical networks (PONs) is proposed, which realizes an upgrade link coexisting with the existing link by pulse position modulation (PPM). In the evolution, the optical distribution network and existing optical network units remain with no changes. The coexisting brings in crosstalk from the upgrade PON link to the existing PON link. The crosstalk is reduced by PPM because PPM provides good suppression at low frequency and high receiving sensitivity. The coexisting scheme is experimentally demonstrated and error free operation is achieved for both the existing signal and the upgrade signal. The tested power penalty of the existing signal coexisting with the upgrade signal in PPM is ~0.5 dB, better than Manchester code, which has been considered as the best candidate for upgrade signal modulation. Taking code efficiency into consideration, the PPM with four pulse positions (4PPM) shows the best performance in the coexisting evolution.