With OM3, Why Do We Still Need OM4 Fiber Cable?

The fiber rollout in a Data Center is  mostly dominated by the multimode fibers classified by the OM1 to OM4 standards. The single mode fibers are dominating the backbone infrastructures due to their long reach capabilities determined by the core diameter that allow a single mode light distribution along the fiber.

Multi-mode fibers are described using a system of classification determined by the ISO 11801 standard — OM1, OM2, and OM3 — which is based on the modal bandwidth of the multi-mode fiber. For many years 62.5/125 µm (OM1) and conventional 50/125 µm multi-mode fiber (OM2) were widely deployed in premises applications. These fibers easily support applications ranging from Ethernet (10 Mbit/s) to gigabit Ethernet (1 Gbit/s) and, because of their relatively large core size, were ideal for use with LED transmitters. Newer deployments often use laser-optimized 50/125 µm multi-mode fiber (OM3). Fibers that meet this designation provide sufficient bandwidth to support 10 Gigabit Ethernet up to 300 meters. Optical fiber manufacturers have greatly refined their manufacturing process since that standard was issued and cables can be made that support 10 GbE up to 400 meters. Laser optimized multi-mode fiber (LOMMF) is designed for use with 850 nm VCSELs.

The migration to LOMMF/OM3 has occurred as users upgrade to higher speed networks. LEDs have a maximum modulation rate of 622 Mbit/s because they cannot be turned on/off fast enough to support higher bandwidth applications. VCSELs are capable of modulation over 10 Gbit/s and are used in many high speed networks.

OM3 & OM4 Similarities

OM3 and OM4 are both laser-optimized multi-mode 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 connectors is the same. Additionally, both of them are designed for use with 850-nm VCSELS (vertical-cavity surface-emitting lasers) and have aqua sheaths. The cost for OM4 is greater due to the manufacture process and also due to economies of scale that the production of OM3 benefits from due to the volumes currently produced.

The connectors are the same so the difference in OM3 and OM4 performance is in the loss (dB) in the cable. OM4 fiber causes lower losses due its construction. The maximum attenuation allowed by the standards is shown below. You can see that using OM4 will give you lower losses per meter of cable. The lower losses mean that you can have longer links or have more mated connectors in the link. The better the modes are equalized, the higher the bandwidth of the fiber. Mode equalization depends on how well the graded index profile is constructed during fiber manufacturing. The more precise the refractive index profile is in
terms of shape, curvature and smoothness (free of dips, spikes or defects), the better the modes will be equalized.

Color code for easy identification

OM1 and OM2 fibers have orange colour on the exterior while for OM3 and OM4 fibers, their exterior is colored in aqua.

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.

Conclusion

OM4 fiber provides next-generation multimode fiber performance for today and tomorrow’s high speed applications. With its significantly higher bandwidth, network designers and operators can be assured that multimode fiber will continue to provide the most cost effective solutions for short reach applications in data centers and LANs. The
primary benefit that OM4 provides is additional reach at extended bandwidth at an overall cost still less than that of an OS2 singlemode system. In other words, OM4 provides a solution that allows more installations to avoid the significantly higher costs of singlemode systems. The additional bandwidth and lower attenuation of OM4 provide additional insertion loss margin. As a result, users of OM4 gain additional safety margin to help compensate for less-than-ideal cabling installations as well as provide margin for degradation due to moves, adds, and changes over the life of the installation.