With OM3, Will OM4 Still Be Needed?

With the transmission of massive amount of data, there is an increasing demand for higher bandwidth and fast speeds. The basic structure of network—cabling should be upgraded accordingly to meed this demand. For instance, copper cabling is developed from Category 1 to Category 8 cable. Likewise, fiber optic cabling also has its improvement, especially the multimode fibers that have OM1, OM2, OM3 and OM4 cables. OM1 specifies 62.5-micron cable and OM2 specifies 50-micron cable, while OM3 and OM4 are the optimized upgrade of OM2 for higher bandwidth applications, such as 40/100 GbE. However, a lot of confusion has emerged as the use of OM3 and OM4 fiber coexist. OM3 and OM4 seem to have many similarities and same applications. So why do we still need OM4 though we have already had OM3?

Similarities of OM3 and OM4

Both OM3 and OM4 are laser-optimized multimode fiber (LOMMF) and were developed to accommodate faster networks such as 10, 40 and 100 Gbps. They have the same fiber core size 50/125 and the termination of the connections is the same. Moreover, both of them are designed for use with 850nm VCSELS (vertical-cavity surface-emitting lasers) and have aqua sheaths. The picture below is a 10G OM4 SC LC fiber patch cable.

Difference Between OM3 and OM4

With the better fiber cable construction, OM4 fiber (4,700 megahertz) operates at higher bandwidth than OM3 (2,500 megahertz). The higher bandwidth available in OM4 refers to a smaller modal dispersion and thus allows for longer cable links or higher losses through more mated connectors. This provides more options when looking at network design. Besides, OM4 cable has better attenuation that leads lower losses than OM3. The lower losses mean that we have longer links or have more mated connectors in the link.

Actually, the factors that we describe above translate to longer transmission distances for the OM4 fiber. Although OM3 and OM4 can be both applied to 10GbE, 40GbE and 100GbE applications, they have different transmission distance. For 10G network, OM3 can transmit 300 m, while OM4 can transmit 500 m. For 40G and 100G network, OM3 supports 100 m, but OM4 supports 150 m. So OM4 has a better performance than OM3 due to its better cable construction. The primary cost increase of OM4 arises from this. The cost for OM4 is greater due to the manufacture process. Generally, OM4 cable is about twice as expensive as OM3 cable.

OM4 is a laser-optimized, high bandwidth 50 micrometer multimode fiber. In August of 2009, TIA/EIA approved and released 492AAAD, which defines the performance criteria for this grade of optical fiber. It can be used to enhance the system cost benefits enabled by 850 nm VCSELs for the earlier 1 G and 10 Gb/s applications as well as the 40 and 100 Gb/s systems. For example, most of ST to LC fiber jumper from FS.COM is manufactured using laser-optimized, 50/125, OM4 multimode cable, and can achieve max link distance of 50 meters. OM4 fiber can support Ethernet, Fibre Channel, and OIF applications, allowing extended reach upwards of 550 meters at 10 Gb/s for ultra long building backbones and medium length campus backbones. OM4 fiber is also especially well suited for shorter reach data center and high performance computing applications.

Except cost consideration, the availability of standard is the other consideration on using OM3 or OM4. OM3 is much more widely used than OM4 because there is a greater range and depth of standard product available. However, for factory manufactured pre-terminated solutions, the availability is now similar due to the increase in the demand for 40 GbE and 100 GbE. Additionally, OM3 and OM4 are completely compatible. So it is completely viable to mix OM3 product with OM4 and still obtain the required performance.

Conclusion

It is important to note that OM4 glass is not necessarily designed to be a replacement for OM3. Despite the relatively long-standing availability of OM4, there are no plans to obsolete OM3 fiber optic cabling. For most systems, OM3 glass is sufficient to cover the bandwidth needs at the distances of the current installation base. Most system requirements can still be reliably and cost effectively achieved with OM3, and this glass type will remain available for the foreseeable future. Despite the availability of OM4 glass, OM3 is quite capable of 40 and 100 Gb/s applications albeit at significantly shorter distances than OM4. This is why we need OM4 though we have already had OM3. All in all, which one to choose should depend on the network/distance design and cost as well as the future migration plan of your network.