The need for this patch cord is due to the single-mode launch nature of the –LX or long-wave (1300nm) transceiver modules used for Gigabit Ethernet.  These modules have to operate with both single-mode and multimode fibers.  Launching the 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.  Offset point creates a launch that is similar to typical multimode LED from the center of a multimode fiber.  This offset point creates a launch that is similar to typical multimode LED launches.