The classes of cabled multimode fiber. OM1 is 62.5/125 and OM2 is 50/125, both orange jacketed and rated for LED sources at 850 and 1300 nm. OM3 and OM4 are laser-optimized 50 µm fibers rated at 2000 and 4700 MHz-km effective modal bandwidth at 850 nm, usually aqua, with OM4 sometimes in violet. OM5 is lime green and specified across 850 to 950 nm for shortwave wavelength multiplexing.
The drawings say OM4 but the jacket in the tray is printed OM3, so either the sub swapped it or we're pulling the wrong reel.
Mixing OM3 and OM4 in one channel works, but the whole link is rated to the lower grade, so the reach drops to the OM3 numbers.
Do not mix it up with
- OS2: OS grades are singlemode classes; OM grades only describe multimode fiber.
Related terms
Multimode fiber
Fiber with a 50 or 62.5 µm core that carries many light paths at once, used for short links inside buildings and data centers.
OS2
Optical Singlemode 2: the low-water-peak cabled singlemode grade used for most indoor and outdoor singlemode installs.
Fiber color code
The fixed sequence of twelve colors that identifies each fiber and buffer tube in a cable.
Mandrel wrap
Multimode test jumper wound around a smooth rod to strip out high-order modes and stabilize loss readings.