•
Modal dispersion, which is the spreading of the signal over time caused by the different
propagation modes in the fiber.
For multimode transmission, modal dispersion, rather than chromatic dispersion or
attenuation, usually limits the maximum bit rate and link length. For single-mode
transmission, modal dispersion is not a factor. However, at higher bit rates and over longer
distances, chromatic dispersion limits the maximum link length.
An efficient optical data link must have enough light to exceed the minimum power that
the receiver requires to operate within its specifications. In addition, the total dispersion
must be within the limits specified for the typeof link in Telcordia Technologies document
GR-253-CORE (Section 4.3) and International Telecommunications Union (ITU)
document G.957.
When chromatic dispersion is at the maximum allowed, its effect can be considered as
a power penalty in the power budget. The optical power budget must allow for the sum
of component attenuation, power penalties (including those from dispersion), and a
safety margin for unexpected losses.
Related
Documentation
• Calculating the EX Series Switch Fiber-Optic Cable Power Budget on page 89
• Calculating the EX Series Switch Fiber-Optic Cable Power Margin on page 89
121Copyright © 2015, Juniper Networks, Inc.
Chapter 8: Transceiver and Cable Specifications
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