Guide to Multimode Fiber OM1 to OM5 Explained

In fiber-optic communications, the choice between single-mode and multimode fibers is a critical decision for network infrastructure design. This article focuses on multimode fiber (MMF), providing an in-depth analysis of five key types—OM1, OM2, OM3, OM4, and the emerging OM5—examining their core dimensions, transmission characteristics, bandwidth capabilities, and application scenarios to assist engineers and technicians in selection.

I. Core Characteristics of Multimode Fiber

Optical fibers are categorized by the number of light propagation modes they support. Multimode fiber (OM) features a larger core diameter, enabling multiple light paths (modes) to travel simultaneously. Per TIA/EIA standards, OM1 fiber has a 62.5µm core, while OM2–OM5 fibers use a 50µm core. This dimensional difference directly impacts performance and applications.

II. Legacy Fibers: OM1 and OM2

OM1's 62.5µm core creates compatibility challenges with other MMFs, requiring different connectors. Both OM1 and early OM2 fibers were designed for LED light sources, which inherently limited their bandwidth due to LED modulation constraints. Engineers must verify cable markings to ensure proper connector selection.

III. Laser-Optimized Fibers: OM2–OM5

To address growing bandwidth demands, laser-optimized MMFs (LOMMFs) were developed. OM2–OM5 fibers work with vertical-cavity surface-emitting lasers (VCSELs) at 850nm wavelengths, enabling significantly higher data rates than LEDs. Today, laser-optimized OM2 is widely deployed.

IV. Bandwidth and Transmission Distance

Effective Modal Bandwidth (EMB) distinguishes fiber performance. OM3 delivers 2000 MHz·km EMB at 850nm, while OM4 achieves 4700 MHz·km, supporting greater distances at higher speeds. Color coding aids identification: OM2 (orange), OM3/OM4 (aqua), OM4 (optional violet), and OM5 (lime green). All OM2–OM5 fibers share 50/125µm dimensions and connector compatibility, though color codes may vary by manufacturer.

V. Performance Comparison

VI. OM5: Broadband Multimode Fiber

OM5 represents the latest advancement, featuring lime-green jacket identification. While matching OM4's EMB and distance specifications, it uniquely supports shortwave wavelength division multiplexing (SWDM), making it ideal for high-density data center applications.

VII. Selection Guidelines

For most MMF applications, OM3 or OM4 remains optimal. OM3 suffices for residential installations under 300m, while OM4 offers future-proofing for enterprise networks. Decision factors include bandwidth requirements, transmission distances, budget constraints, and scalability needs.