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Cisco 10000 Series Routers Line Card Hardware Installation Guide
OL-6773-04
Chapter 10 1-Port Gigabit Ethernet Half-Height Line Card Overview
SFP Module Configurations and Specifications
Mode-Conditioning Gigabit Ethernet Patch Cord Description
A mode-conditioning patch cord can be used with the SFP-GE-L= (SFP module) to allow reliable laser
transmission between the single-mode laser source on the SFP module 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 Figure 10-4) to a graded-index
multimode optical fiber. Figure 10-4 shows a diagram of the mode-conditioning patch cord assembly.
Figure 10-4 Mode-Conditioning Patch Cord Assembly for an SFP Module
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
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 SFP-GE-L= is compliant with the IEEE 802.3z standard
for 1000BASE-LX.
Go to Chapter 16, “Preparing for Installation” to begin the installation or replacement of the line card.
For troubleshooting information, see Chapter 18, “Troubleshooting the Installation.”
1 Gray color identifier 5 Single-mode bar
2 To Gigabit Ethernet interface 6 Offset
3 Blue color identifier 7 Beige color identifier
4 Multimode bar 8 To cable plant
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