ZyXEL
OLT-2300 Series Support Notes
All contents copyright
ٛ
2006 ZyXEL Communications Corporation.
29
Why single mode is necessary for PON network?
In fiber optic communications, a single-mode optical fiber is an optical fiber
designed to carry only a single ray of light (mode). This ray of light often consists
of a variety of different wavelengths. Although the ray travels parallel to the length
of the fiber, it is often called the transverse mode since its electromagnetic
vibration occur perpendicular (transverse) to the length of the fiber. Single-mode
optical fibers are also called monomode optical fibers, single-mode optical
waveguides, or unimode fibers.
Unlike multi-mode optical fibers, single-mode fibers do not exhibit modal
dispersion resulting from multiple spatial modes. Single-mode fibers are also
better at retaining the fidelity of each light pulse over long distances than are
multi-mode fibers. For these reasons, single-mode fibers can have a higher
bandwidth than multi-mode fibers.
Why do we need PON not point-to-point fiber network?
In order to bring the fiber network to a home, in the past, the straightforward way
to deploy optical fiber in the local access network was to use a point-to-point (P2P)
technology with dedicated fiber running from the CO to each end user subscriber
(Fig. A). This is a simple architecture, however in the most cases its cost is
prohibitive because it requires significant outside fiber plant deployment as well as
connector termination space in the local exchange. Considering N subscribers at
an average distance L km from CO, a P2P design requires 2N transceivers and N
