Cisco 7401ASR Installation And Configuration Manual page 54

Chapter 2 Rack-Mounting, Tabletop Installation, and Cabling
Connecting I/O Cables
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 2-14) to a graded-index
multimode optical fiber. Figure 2-14 shows a diagram of the mode-conditioning patch cord assembly.
A 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 1000BASELX and 1000BASELH 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 is compliant with the IEEE 802.3z standard for
1000BASELX.
Cisco 7401ASR Installation and Configuration Guide
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OL-5419-01 B0