Have you ever wondered what multimode optical fibers actually are and why they come in different types? The abbreviation OM comes from Optical Multimode and stands for multimode fiber optics, which are a key component in local area networks (LANs), or data centers. The division into OM1, OM2, OM3, OM4 (and also OM5) helps sort out their technical characteristics, such as core diameter, bandwidth and maximum transmission distances. 

 

What is meant by multimode fiber? 

Multimode fiber optics (MMF) are optical cables with a wide core (50 µm or 62.5 µm), allowing light to travel in multiple “modes” simultaneously - that is, at different angles to the cable axis. Mods, in short, are the different paths by which light can travel through the cable's wide core. This increases throughput, but also poses challenges in terms of signal precision due to the phenomenon of so-called modal dispersion (signal blurring caused by different times for light mods to reach the end of the cable). Therefore, transmission with multimode fibers is relatively short. However, cheaper and simpler to install with respect to single-mode cables, multimode cables are great for short-distance indoor connections (e.g. in a server room or on the floor of an office building).  

 

What is OM1, OM2, OM3, and OM4? 

The division into OM1, OM2, OM3 and OM4 (and the latest OM5) is due to the evolution of fiber-optic technology and increasing data bandwidth requirements. Each generation has its own characteristics, such as core diameter, modal bandwidth and maximum transmission distance. 

 

Characteristics of the different generations of fiber optics

 

Type 

Diameter of the core 

Light source 

Range

Cable color 

OM1 

62,5 µm 

LED 

Up to 33 m in 10G networks

Orange 

OM2 

50 µm 

LED 

Up to 82 m in 10G networks

Orange

OM3 

50 µm 

VCSEL 

Up to 300 m in 10G networks

Aqua

OM4 

50 µm 

VCSEL 

Up to 550 m in 10G networks, up to 150 m in 40/100G networks  

Aqua

OM5 

50 µm 

VCSEL  

Do 440 m w sieci 40G, do 150 m w sieci 100G 

Lime green 

 

Can different types of fiber optics be joined together? 

Yes, if they have the same core diameter and are designed to handle the same type of light source. More details below. 

OM1 with OM2/OM3/OM4 

Combining cables with different core diameters (62.5 µm and 50 µm) can cause: 

  • Signal loss: modal mismatch results in loss of optical energy. 
  • Limiting the transmission distance: The network can work properly, but at much shorter distances. 

If you must already connect these cables, special optical adapters are required.  

OM3 and OM4 

These optical fibers are compatible with each other. They have identical core diameters (50 µm) and support the same VCSEL technologies. The differences are mainly in the lengths at which they achieve maximum throughput: 

  • OM3: up to 300 m at 10 Gbps. 
  • OM4: up to 550 m at 10 Gbps. 

Combining the two will not adversely affect performance, although limitations will result from the parameters of the weaker cable. 

How to minimize problems when mixing cables? 

  • Use high-quality optical adapters. 
  • Regularly test your network for signal loss and performance. 
  • Avoid long connections on mixed fibers 

 

Summary - how to combine fiber optics of different generations? 

Mixing different types of fiber optics is possible, but requires knowledge of their technical specifications. OM3 and OM4 work well together, while mixing OM1/OM2 with OM3/OM4 requires caution due to differences in core diameter and light source technology. When upgrading networks, it is best to aim for unified standards and use the highest-performance cables, such as OM4 or the latest OM5.