Why You Might Need to Use a Mode Conditioning Fiber Optic Patch Cord
March 31st, 2009 by Jay Sumner
Mode Conditioning Patch Cord
What is a Mode Conditioning Patch Cord? A mode conditioning patch cord is a duplex multimode cord that has a small length of singlemode fiber at the start of the transmission leg. The basic principle behind the cord is that you launch your laser into the small section of single mode fiber. The other end of the singlemode fiber is coupled to multimode section of the cable with the core offset from the center of the multimode fiber. The laser light thus misses the “dip” and this new launch condition more closely mimics a standard LED launch. The bonus is that you still retain the speed advantages of using a laser.
A Mode Conditioning Patchcord (MCP) creates an offset in the launch from the laser into the multimode fiber, avoiding the index dip in the center of the fiber and allowing the signal to propagate properly through the fiber. Newer “Laser Enhanced” multimode fibers do not exhibit this phenomenon due to the engineering of the fiber without an index dip in the core.
In legacy fiber optic systems, multimode fibers were not designed to properly transmit a SM laser source without the creation of dispersion problems, where the original signal becomes spread out over distance (>300m in most systems) and pulses can combine with each other creating an unreadable signal at the receiving end. This was caused by a small dip in the Index of Refraction profile of the fiber in the center of the core in which the laser transmission becomes “mode locked”.
Tags: laser, LED, mode conditioning fiber optic patch cord, multimode