Passive optical network (PON) architectures and systems of today are not efficient in utilizing capacity and spectrum. The daily usage patterns and the ever-growing bandwidth demand in access require a transport technology that is dynamically operated and that is based on wavelength division multiplexing (WDM). FlexPON is designed to meet those requirements: it combines a reconfigurable WDM layer with “on-demand” time division multiple access (TDMA) and wavelength-agnostic optical networking units (ONUs). As such, it enables flexible capacity planning between such stacked TDMA/WDM PONs on single fiber architectures. In this work, progress is reported on multi-wavelength transmitter (TX) and receiver (RX) sub-systems that are used at the optical line termination (OLT) at the central office. The Indium Phosphide (InP)-based application specific photonic integrated circuits (ASPICs) are realized following the generic integration method proposed by the European EuroPIC project. Static and dynamic measurements are shown. The TX8-channel ASPIC is operated at 12.5 Gbps in a back-to-back (BTB) and 20 km standard single-mode fiber (SSMF) configuration. Error-free BTB operation at 10 Gbps is obtained employing a 231 -1 pseudo random bit sequence (PRBS).