Jan. 27, 2021 - Cleerline has spoken frequently in the past about the difference between single mode and multimode fiber and on the distance limitations between fiber types.

However, there are 5 grades of multimode fiber: OM1, OM2, OM3, OM4, and now OM5.  What exactly makes them different?

At the core (pardon the pun), what separates these fiber grades are their core sizes, transmitters, and bandwidth capabilities.

Optical multimode (OM) fibers have a core of 50 µm (OM2-OM5) or 62.5 µm (OM1).  The larger core means that multiple modes of light travel down the core at the same time, thus the name "multimode."

Legacy Fibers

Importantly, OM1’s 62.5 µm core size means that it is not compatible with other grades of multimode and cannot accept the same connectors.  Since OM1 and OM2 can both have orange outer jackets (per TIA/EIA standards), always check the print legend on the cable to ensure you are using the correct connectors.

Early OM1 and OM2 fibers were both designed for use with LED sources or transmitters.  The modulation limitations of LEDs likewise limited the capabilities of OM1 and early OM2. 

However, the increasing need for speed meant that optical fibers needed higher bandwidth capabilities.  Enter the laser-optimized multimode fibers (LOMMF):OM2, OM3 and OM4, and now OM5. 

Laser-Optimization

OM2, OM3, OM4, and OM5 fibers are designed to work with vertical-cavity surface-emitting lasers (VCSELs), generally at 850 nm.  Today, laser-optimized OM2 (such as ours) is also readily available.  VCSELs allow far faster modulation rates than LEDs, meaning that laser-optimized fibers can transmit far more data.  (For an in-depth overview of Fiber Optic Transmitters, we recommend the Fiber Optic Association’s recent article on the subject.) 

Per industry standards, OM3 has an effective modal bandwidth (EMB) of 2000 MHz*km at 850 nm.  OM4 can handle 4700 MHz*km. 

In terms of identification, OM2 maintains the orange jacket, as noted above. OM3 and OM4 can both have an aqua outer jacket (this is true of Cleerline OM3 and OM4 patch cables).  OM4 can alternatively appear with an "Erika violet" outer jacket.  If you run into a bright magenta fiber optic cable, it’s probably OM4.  Happily, OM2, OM3, OM4, and OM5 are all 50/125 µm fibers and can all accept the same connectors. Note, however, that connector color codes vary. Some multimode connectors may be marked as "optimized for OM3/OM4 fiber" and will be colored aqua. Standard laser-optimized multimode connectors can be beige or black. If there is confusion, please check the connector specification specifically in regard to core size. Matching the core size is the most important attribute for mechanical connectors, as it ensures that the signal will maintain continuity through the connector.

OM5?

OM5 is a wideband multimode fiber, identifiable by a lime green outer jacket.  It has many of the same characteristics of OM4, including the same EMB and distance limitations for 10 GB, 40 Gb, and 100 Gb Ethernet.  OM5 is really intended for data centers and high speed applications, situations that require shortwave division multiplexing (SWDM).

For most applications requiring multimode fiber, we recommend either OM3 or OM4. Particularly, OM3 remains our choice for most residential installations with cable distances of 300 meters (1000 feet) or less.