Passive Optical Networks

users for voice services. A ubiquitous twisted copper network has been deployed

by telephone companies (the Bell System in the United States and PTTs in other

countries) in industrialized countries for decades. It is not difficult to imagine

that such networks were optimized for analog voice frequency transmissions. As

a matter of fact, in order to achieve better economy and allow longer local loop

drops, inductors called loading coils have been installed in many old twisted

copper pair plants to enhance the voice frequency band performance. Loading

coils, however, significantly attenuate high frequency signals outside the voice

frequency band and make them unsuitable for broadband digital subscriber line

(DSL) services.

Although voice signal transmission ...