Mode Conditioning Cable Selector

Things to know when using mode conditioning cables to patch an existing multimode cable plant to your Gigabit LX equipment.

• Mode conditioning cable are normally used in pairs. That means that you will need a MC cable at each end to connect the equipment to the cable plant. So then these cables are usually ordered in even numbers. The usual reason why someone may order one cable is so they may keep it as a spare.
• If your gigabit LX switch is equipped with SC or LC connectors, please be sure to connect the yellow leg (Singlemode) of the cable to the transmit side, and the orange leg (multimode) to the receive side of the equipment. It is imperative that this configuration be maintained on both ends. The swap of transmit and receive can only be done at the cable plant side. (see diagram below)
• Please see Frequently asked questions below for additional important information.

Principals and Basics on how a Mode Conditioning Cable works

The launch of the light coming out of the equipment begins on a Singlemode fiber. The Singlemode fiber is precision fusion spliced to the multimode fiber to a precise core alignment (see fig. 1). The light is launched on to the multimode fiber at a precise angle, giving the cable its mode conditioning properties. Looking at the mode conditioning cable assembly in figure 2, we can see that the fusion splice this protected by a black over-wrap. notice that on the right side there is an orange and a yellow cable. This is the side of the cable that connects to the gigabit equipment with the yellow Singlemode leg connecting to the transmit side.

The great demand for increased bandwidth has prompted the release of the 802.3z standard (IEEE) for Gigabit Ethernet over optical fiber. 1000Base-LX requires the use of a launch conditioning patch cord to allow for proper propagation of the laser VCSEL light along the multimode fiber.

The Mode Conditioning Patch Cord is designed for long wave (-LX) multimode applications of Gigabit Ethernet. It is compliant with this IEEE 802.3z application standard. This patch cord consists of duplex SC connectors on each end of a cable assembly with a single-mode fiber offset to a multimode fiber connection point in between.

The need for this patch cord is due to the single-mode launch nature of the -LX or long-wave (1300 nm) transceiver modules used for Gigabit Ethernet. These modules have to operate for both single-mode and multimode fibers. Launching a single-mode laser into the center of a multimode fiber can cause multiple signals to be generated that confuse the receiver at the other end of the fiber. These multiple signals, caused by Differential Mode Delay (DMD) effects, severely limit the cable distance lengths for operating Gigabit Ethernet. A mode conditioning patch cord eliminates these multiple signals by allowing the single-mode launch to be offset away from the center of a multimode fiber. This offset point creates a launch that is similar to typical multimode LED launches.