Passive optical networks (PONs) are one of most massively deployed optical access systems because of low cost and high-bandwidth provision. In PON systems, multiple optical network units (ONUs) at the customer sides share the fiber plant and an optical line terminal (OLT) located at the central office. In order to economically support future bandwidth growth, the simplification of today’s telecom networks requires an architecture to combine metro and access networks. As a result, the metro network is getting absorbed in access and the traditional access service node is moving close to the backbone nodes.

While metro/access convergence significantly reduces operational expenditure (OpEx) by consolidating the network elements, it introduces novel challenges for the physical layer component technology, esp. the head-end receivers at the OLT. While the power and phase variation can be adapted from burst to burst, the ability to recover bursts with a wide range of distortion/dispersion is not yet available in today's PON receivers. Therefore, a fundamental research towards a more comprehensive knowledge or understanding of upstream impairment mitigation for next-generation optical access is necessary.