Passive Optical Networks

The optical access is gaining more interest as the demand for higher and higher bandwidth is getting stronger. The major drivers for larger bandwidth are the increasing processing power of user terminals and development of services that require substantially larger bandwidth than available in present day access networks. The prevailing access techniques, such as the digital subscribes line systems and cable modems, are capable of supporting up to few tens of Mbit/s access rates per user, but the transport distance is limited. The optical access offers significantly higher bit rates and longer transport distances. The high cost has been the foremost factor that has been slowing down penetration of the optical access. A number of alternative transport concepts have been developed to tackle the cost problem as well as the technical ones. The passive optical network techniques are largely anticipated to be the most economical solutions. This publication surveys the state of the art of the optical access concentrating on explaining more thoroughly some of the best known concepts. The survey is complemented with an assessment of the viability of the most well known concepts. Finally network costs of some optical transport concepts are compared based on the utilisation of the transport channel capacity.