Mode-Conditioning Patch Cord Description - Cisco 7304 Installation And Configuration Manual

Chapter 1 NSE-100 Overview
For more detailed information on these GBIC modules, see the
Sheet.

Mode-Conditioning Patch Cord Description

A mode-conditioning patch cord can be used with the GBIC-LH or WS-G5486 to allow reliable laser
transmission between the single-mode laser source on the GBIC and a multimode optical fiber cable.
When an unconditioned laser source designed for operation on single-mode optical fiber is directly
coupled to a multimode optical fiber cable, an effect known as differential mode delay (DMD) might
result in a degradation of the modal bandwidth of the optical fiber cable.
This degradation results in a decrease in the link span (the distance between a transmitter and a receiver)
that can be supported reliably. The effect of DMD can be overcome by conditioning the launch
characteristics of a laser source. A practical means of performing this conditioning is to use a device
called a mode-conditioning patch cord.
A mode-conditioning patch cord is an optical fiber cable assembly that consists of a pair of optical fibers
terminated with connector hardware. Specifically, the mode-conditioning patch cord is composed of a
single-mode optical fiber permanently coupled off-center (see Offset in
multimode optical fiber.
The mode-conditioning patch cord assembly is composed of duplex optical fibers, including a
single-mode-to-multimode offset launch fiber connected to the transmitter, and a second conventional
graded-index multimode optical fiber connected to the receiver. The use of a plug-to-plug patch cord
maximizes the power budget of multimode 1000BASE-LX and 1000BASE-LH links.
The mode-conditioning patch cord is required to comply with IEEE standards. The IEEE found that link
Note
distances could not be met with certain types of fiber-optic cable cores. The solution is to launch light
from the laser at a precise offset from the center, which is accomplished by using the mode-conditioning
patch cord. At the output of the patch cord, the GBIC-LX/LH is compliant with the IEEE 802.3z standard
for 1000BASE-LX.
Figure 1-5
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RX
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OL-3967-01
Figure 1-5
Mode Conditioning Patch Cord
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TX
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Gray color identifier
To Gigabit Ethernet interface
Blue color identifier
Multimode bar
Gigabit Ethernet GBIC Port and Cabling Specifications
shows a diagram of the mode-conditioning patch cord assembly.
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Offset
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5 Single-mode bar
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Offset
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Beige color identifier
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To cable plant
Cisco 7304 Network Service Engine Installation and Configuration
Cisco Gigabit Interface Converter Data
Figure 1-5) to a graded-index
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