How to read markings on multimode optical fibers

Multimode optical fibers are identified using standardized color codes, printed legends, and jacket markings that indicate fiber type, count, and performance category.Fiber Color Codes

Multimode fibers follow the TIA-598-C standard, which assigns a specific color to each fiber within a cable. The standard 12-color sequence is:

1. Blue
2. Orange
3. Green
4. Brown
5. Slate
6. White
7. Red
8. Black
9. Yellow
10. Violet
11. Rose
12. Aqua For cables with more than 12 fibers, the sequence repeats, often with stripes or tube-based identification to maintain unique numbering. For example, in a 48-fiber cable, the 34th fiber would be identified by its tube color and its position within that tube (e.g., Violet fiber in a Green tube) to avoid confusion .

Printed Legends and Jacket Markings

The outer jacket of a multimode fiber cable typically includes printed information such as:

• Fiber count: e.g., “12F” for 12 fibers, “24F” for 24 fibers
• Fiber type: OM1, OM2, OM3, OM4, or OM5, indicating core size and performance
• Core/cladding dimensions: e.g., 50/125 µm or 62.5/125 µm
• Cable construction and rating: e.g., OFNR (riser), FT4 (fire rating), armored or nonconductive These markings are essential for confirming compatibility with connectors, network equipment, and installation environments.

Jacket Colors and OM Categories

Multimode fibers often use jacket colors to indicate the OM category:

• OM1: Orange jacket, 62.5/125 µm core
• OM2: Orange jacket, 50/125 µm core
• OM3 & OM4: Aqua jacket, 50/125 µm core, laser-optimized
• OM5: Lime green jacket, 50/125 µm core, wideband multimode for SWDM Always verify the printed legend on the jacket, as some manufacturers may use custom colors while still complying with TIA-598-C standards .

Identifying Individual Fibers

To identify a specific fiber in a multi-fiber cable:

1. Check the tube color if the cable uses a tube-and-fiber system for high-count cables.
2. Determine the fiber's position within the tube using the 12-color sequence.
3. Combine tube and fiber color to uniquely identify the fiber for splicing or termination .

Connector and End-Face Colors

Connector colors also provide clues:

• Blue: UPC (Ultra Physical Contact)
• Green: APC (Angled Physical Contact) These indicate the polish type and are critical for proper mating and minimizing return loss .

Summary

Reading multimode fiber markings involves interpreting jacket colors, printed legends, fiber color codes, and connector types. By following TIA-598-C standards and checking the cable's print legend, technicians can accurately identify fiber type, count, and position, ensuring correct installation, splicing, and network performance.