OM1 (Optical Multimode 1) is a type of multimode fiber optic cable. It has a core size of 62.5 micrometers and is commonly used in older fiber optic installations. While OM1 is suitable for lower data rates, its bandwidth limitations make it less ideal for higher-speed applications like 10 Gigabit Ethernet (10GbE).

The reach of OM1 fiber for 10GbE is limited due to its lower bandwidth and higher modal dispersion compared to newer multimode fiber types such as OM3 or OM4. Typically, OM1 is recommended for shorter-distance connections at lower data rates.

For 10GbE applications using OM1 fiber:

• Short Distances: OM1 can support relatively short distances, such as up to 33 meters (around 108 feet) for standard 10GbE transmission.

It's important to note that the practical reach of OM1 for 10GbE depends on various factors, including the quality of the fiber, the type of transceivers used, and environmental conditions. If longer distances or higher data rates are required, it's advisable to consider using newer multimode fiber types, such as OM3 or OM4, which offer higher bandwidth and support longer distances for 10GbE applications.

Many enterprise networks are moving beyond 1000BASE-SX and transitioning to 10 gigabit networks, such as 10GBASE-SR. This is where distance considerations really come into play. A network using OM1 has a maximum distance of 275 meters for 1000BASE-SX, but it would see a distance limit of only 33 meters for 10GBASE-SR. Similarly, OM2 fiber for 1000BASE-SX has a 550 meter limit, but drops down to 82 meters for 10GBASE-SR. The introduction of OM3 increased that distance to a more usable 300 meters in the enterprise.

The distance limit for 10 Gb/s over OM4 is listed at 400 meters in the above chart. This limit is set by TIA and IEEE standards based on worse case assumptions. However, these distances can likely extend out to 500 or 550 meters. The 400-meter limit is based on the transceiver having a spectral width of 0.65 nanometers, but most of these transceivers today are 0.47 nanometers, so you can typically extend farther than 400 meters. That’s a conversation you need to have with the cabling manufacturer.

40 AND 100 GB/S NETWORKS
When considering multimode for 40 gigabit Ethernet — namely 40GBASE-SR4 using four transmitters and four receivers — you will need an MPO-style connector, and you can’t use older OM1 or OM2 fiber. Also, the distance limits will drop to 100 meters for OM3 and 150 meters for OM4. The original intent of 40GASE-SR4 was for the data center, with the vast majority of the links in data centers under 100 meters. But enterprise links are typically much longer than 100 meters. These networks will likely deploy 10GBASE-SR throughout the campus, and then 40GBASE-SR4 in server rooms or communications rooms.

Moving to 100GBASE-SR4 reduces the supported length further to 70 meters over OM3 and 100 meters over OM4, which is why we are seeing an increase in the deployment of OM4 fiber and the consideration of single-mode, as it is not so distance limited