Understanding the Difference Between OM4 and OM5, Part 1

In part one of this two-part blog, we review the key characteristics of the multi-mode fiber specified by the ISO/IEC 11801 standard. Part two will detail when OM4 is preferable and when users can derive benefit from using OM5.

Multi-mode fiber is a mainstay of the data center and campus networking space. However, it can be a challenge to choose the specific type of multi-mode fiber for your cable infrastructure. Of the five classes of multi-mode fiber specified by the ISO/IEC 11801 standard, three are in common use: OM3, OM4 and the most recently defined version, OM5. OM5 may be difficult to understand, particularly its capabilities and when it provides advantages over OM4. To clarify the situation, we review the standard and how to quantify the fiber's performance.

The effect of core diameter on fiber modes

Light propagates through an optical fiber as a collection of spatial modes. Each mode travels a different optical path down the fiber, with a varying transit time. The wider the core diameter of the fiber, the greater the number of modes it can support. Single-mode fiber has a core diameter 8 to 10