Chapter 10 1-Port Gigabit Ethernet Half-Height Line Card Overview
SFP Module Configurations and Specifications
Mode-Conditioning Gigabit Ethernet Patch Cord Description
Amode-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 10-4shows a diagram of the mode-conditioning patch cord assembly.
Figure 10-4 Mode-Conditioning Patch Cord Assembly for an SFP Module
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 |
| | | |
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.”
| | Cisco 10000 Series Routers Line Card Hardware Installation Guide | | |
| | |
| OL-6773-04 | | | 10-11 | |
| | | |
