What is Multimode fiber?
Multimode fiber has a core much wider than single-mode, so light can travel along many paths at once. This makes connectors and light sources less costly and easier to align, but the signals spread as they travel, which limits the distance at high speeds. Its main use is short links in buildings and data centers.
Multimode fiber is graded by OM class. OM1 uses a 62.5 micrometer core, while OM2, OM3, OM4 and OM5 use a 50 micrometer core, with higher grades supporting higher speeds or longer distances. OM3 and OM4 are laser optimized for use with VCSEL-based transceivers. The classes are defined in ISO/IEC 11801 and related TIA standards.
Multimode fiber should not be mixed with single-mode at the same link. The transceivers and the fiber must match. Mixing core sizes within multimode, such as 62.5 and 50 micrometer, can also cause losses, so check what is already installed before adding cable.
How it shows up in practice
- Identify existing fiber grades before ordering, for example by reading the cable jacket print and the documentation.
- Match the transceiver to the fiber grade and the link distance the application needs.
- Use consistent patch cords and polarity for multi-fiber links, and label both ends.
- Test and clean every connection, since dirt is a common cause of errors.