The difference between OM3 and OM5 multimode fiber

This article details the specifications of the major multimode fiber standards developed to support new high-speed applications and helps you determine whether you need to upgrade multimode fiber, or if your existing fiber is adequate.

multimode fiber

1. Application and specification of multimode fiber

The original multimode fiber (MMF) standard ANSI/TIA-492AAAA (OM1, 62.5/125 µm) was published in 1989 to support Fast Ethernet 100BASE-FX and 1000BASE-SX Ethernet with a high numerical aperture (NA) network of 0.275 . and capture light from a 1300 nm LED light source.

The ANSI/TIA-492AAAB standard (50/125 µm) for OM2 was published in 1998, improving the modal bandwidth and reducing it by 0.2 (n/a) to support higher data transfers, such as 1 Gbps VCSELs for longer distances.

To meet the growing bandwidth demands, laser-optimized multimode fiber (LOMMF) standards OM3 and OM4 with effective modal bandwidth (EMB) of 2000 MHz∙km and 4700 MHz∙km were developed in 2002 and 2009 respectively to support 10G , 40G and 100G Ethernet applications as well as InfiniBand and Fiber Channel protocols.

Historically, multimode optics have operated at a single wavelength. The MMF standards (OM1/OM2/OM3/OM4) only specify minimum bandwidths of 850nm and 1300nm (for 10G or higher system speeds, 1300nm LEDs are no longer used). More recently, however, the TIA and ISO/IEC organizations developed and standardized OM5 (Wideband MMF) to support Short Wavelength Division Multiplexing (SWDM) from 840 nm to 953 nm.

2. Multimode fiber (MMF) reaches its limit

Although OM1 and OM2 multimode fibers have been widely deployed in the past, they are no longer suitable for new Ethernet infrastructure deployments—primarily due to the inherent limitations of EMB. Let's take a closer look at the potential risks you may face when reusing old OM1 and OM2 cables without completing a fiber upgrade.

When used with the newer MMF type (50µm core), the OM1 (62.5µm core) has a different fiber geometry that causes excessive signal loss even at short distances.

OM1 and OM2 only support very limited links above 1G, and no longer support system speed upgrades. In the new ANSI/TIA-568.3-D standard, OM1 and OM2 MMF types have been adopted and are not recommended for new greenfield installations.

multimode fiber

OM1 and OM2 have higher cable attenuation (3.5 dB/km) compared to OM3, OM4 and OM5 (3.0dB/km); therefore, it may not be possible to meet a proper connection budget.

Currently, OM3 and OM4 are the most popular MMF types in modern data centers. OM5 has only recently hit the market, so we'll see how long it takes to add OM5 to this list of popular MMF types.

OM3 MMF can support a wider range of the latest Ethernet and Fiber Channel applications. However, care must be taken when pairing older OM3 MMFs with newer bend-insensitive MMFs (BI-MMF). Small differences in fiber geometry can cause additional losses that can negatively impact cable performance.

OM4 BI-MMF is recommended for new fiber installations or fiber upgrade and replacement projects, as the latest applicable standards are based on the OM4 specification.

OM5 is backward compatible with OM4, so it supports the same scope of current applications. Its main difference is the support for transmitting multiple wavelengths on a single MMF thread. When paired with OM5, SWDM-based transceivers can greatly reduce fiber optic cable and connection costs for point-to-point connections. SWDM standard specifications and products are currently under development.

OM4 fiber

In some practical use cases, old fiber optic cables can be re-used for new applications (depending on the fiber type), and as long as the fiber capacity is not limited, no fiber upgrade is required. However, this is not always the case without full knowledge of the link loss budget and transmission costs.

When doing network speed upgrades, our recommendation is to replace old OM1/OM2 or old OM3 with high-quality OM4 BI-MMF cables to prevent light from escaping and causing attenuation caused by bends. This results in better performance, higher bandwidth capabilities and improved optical performance. We also recommend that you take a close look at OM5 if you plan to use SWDM-based transceivers for future fiber upgrades.