Introduction to Passive Optical Networks

Passive Optical Networks (PONs) are based on optical links for which all of the general observations in the section "Optical Communications Basics" in Chapter 6 hold unchanged. A PON is a network in which a plurality of stations are connected to each other by means of a fiber-optical network that does not contain any active equipment; the different fiber segments to which the stations are attached are coupled together by means of a passive (not electrically powered) optical coupler or splitter; this is a device that splits optical power from one fiber into multiple fibers and vice versa.

In contrast, the term "active star" is used to designate a network consisting of a central piece of active equipment (e.g., an Ethernet switch) to which different stations are connected by means of a fiber link. In respect to the active star, a PON has the advantages of not requiring electrical power in the field (thus reducing maintenance cost) and of reducing the total distance of fiber that needs to be deployed for a given set of subscribers, assuming that the splitter can be placed closer to the subscribers than active equipment would be. The PON equipment at the Central Office (CO) terminates only a single fiber for a number of subscribers, using less space and...