Multimode Optical-Fiber Cable

Multimode optical fiber is most often used as backbone cable inside a building and for horizontal cable. Multimode cable permits multiple modes of light to propagate through the cable and thus lowers cable distances and has a lower available bandwidth. Devices that use multimode fiber-optic cable typically use light-emitting diodes (LEDs) to generate the light that travels through the cable; however, higher-bandwidth network devices such as Gigabit Ethernet are now using lasers with multimode fiber-optic cable. ANSI/TIA-568-C.3 recognizes two types of multimode optical fiber cable:

• Two-fiber (duplex) 62.5/125-micron (aka OM1 per ISO 11801)
• 50/125-micron multimode fiber-optic cable

Within the 50/125-micron multimode fiber-optic classification, there are two options:

• A standard 50-micron fiber (aka OM2 per ISO 11801)
• A higher bandwidth option known as 850nm laser-optimized 50/125-micron (aka OM3)

ANSI/TIA-568-C.3 recommends the use of 850nm laser-optimized 50/125-micron (OM3) since it has much higher bandwidth and supports all Gigabit Ethernet applications to the longest distances.

The same connectors and transmission electronics are used on both 62.5/125-micron and 50/125-micron multimode fiber-optic cable. Since multimode fiber has a large core diameter, the connectors and transmitters do not need the same level of precision required with single-mode connectors and transmitters. As a result, they are less expensive than single-mode parts.