Passive Optical Networks

6.2.3 Network Type

Conventional PONs usually support one (for video) or two (for data and

video) downstream optical carriers, as well as one upstream optical carrier.

These optical carriers are time-shared among all ONUs. In order to enable the

delivery of higher capacity services to the subscribers and enhance the flexibility

for network upgrade, PONs using WDM techniques, namely WDM-PONs, have

recently emerged and have aroused much research interests. In WDM-PONs,

each ONU is served by a set of dedicated and distinct wavelength channels to

communicate with the OLT. The ranging problem in conventional time-shared

PONs is also alleviated, as all upstream wavelengths are multiplexed at the RN

without any signal collision. Each individual ONU enjoys