I would also like to add that With the recent advancements in access networks the TDM PON, like Ethernet passive optical network (EPON) and Gigabit Passive optical network (GPON), are now widely used as optical access network solutions to distribute reasonably high bandwidths to the customers through an optical fiber network infrastructure. Researchers are aiming at optical access network concepts known as hybrid WDM/TDM access passive optical networks.
Various techniques and components of the network are designed to achieve high data rate transmission to large bandwidth such as tuneable optical add/drop multiplexer (OADM) , colorless ONU , selfhomodyne and differential coding , a reflective semiconductor optical amplifier (SOA) and Bragg reflectors. The passive optical networks are constituted of a centralized
OLT located in the central office and a number of ONUs located at the users premises to some distance away from the OLT.
I hope this is useful