Fiber optic patch cables play an important role in fiber optic connection. There are numbers of fiber patch cables on the market, ranging from the standard fiber patch cables to special fiber patch cables, such as mode conditioning patch cables, bend insensitive patch cables, traceable fiber patch cables, etc. This article will not introduce all of these fiber jumpers, only focus on the mode conditioning patch cables.
Why Need Mode Conditioning Cables?
Transceiver optics used in Gigabit Ethernet (1000BASE-LX) launch only single-mode long wave signals (1310 nm). This poses a problem if an existing fiber network utilizes multimode cables. When a single-mode signal is launched into a multimode fiber, the phenomenon known as DMD (differential mode delay) can create multiple signals within the multimode fiber. This effect can confuse the receiver and produce errors. Mode conditioning cables utilize an offset between the single-mode fiber and multimode fiber to eliminate DMD and the resulting multiple signals allowing use of 1000BASE-LX over existing multimode fiber cable system.
What Are Mode Conditioning Fiber Patch Cables?
Mode conditioning patch cables are required when Gigabit 1000BASE-LX routers and switches are installed into existing multimode cable plants. They are used to adapt the single-mode output of Gigabit Ethernet (1000BASE-LX) transceivers to a multimode cable network. They are fully compliant with IEEE 802.3z application standards.
The conditioned channel of mode conditioning patch cables consists of a single-mode fiber which has been fusion spliced to a multimode fiber in an offset manner, with a precise core alignment and angle. The non-conditioned channel of mode conditioning patch cables consists of one length of multimode cable. Light is launched on to the multimode fiber of the conditioned channel at a specific angle, giving the patch cord its mode conditioning properties. The fusion splice is protected by a black over-wrap. The other side has both a multimode and single-mode cable end. This side of the cable connects to the Gigabit transceiver equipment with the single-mode leg connecting to the transmit side. The side has two multimode cable ends connecting to the cable plant.
Things You Should Know When Using Mode Conditioning Patch Cables
Use mode conditioning patch cables in pairs. It means that you will need a mode conditioning patch cable at each end to connect the equipment to the cable plant. So then these cables are usually ordered in even numbers. The only reason to order an odd number of mode conditioning cables is to have a spare on hand. Mode conditioning patch cables can only convert single-mode to multimode. If you want to convert multimode to single-mode, then a media converter will be required.
If your Gigabit LX switch is equipped with SC or LC connectors, please be sure to connect the yellow leg (single-mode) 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.
If some customers remain reluctant to deploy MCP cables, and for customers using OM3 or OM4 cables, please measure the power level before plugging the fiber into the adjacent receiver. When the received power is measured above -3dBm (in 1000BASE-LX links), a 5-dB attenuator for 1300 nm should be used and plugged at the transmitter source of the optical module on each side of the link. Actually, OM3/OM4 MCP can also work in this event. While whether all multimode fiber types require mode conditioning, you can contact the manufacturer of your installed cable for the answer.
Mode conditioning patch cables are duplex multimode cords that have a small length of single-mode fiber at the start of the transmission leg. The basic principle behind the cords is that you launch your laser into the small section of single-mode fiber. The other end of the single-mode fiber is coupled to multimode section of the cable with the core offset from the center of the multimode fiber.