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) of 0.275 network. and capture light from a 1300 nm LED light source.
The ANSI/TIA-492AAAB standard (50/125 µm) for OM2 was published in 1998 with improved modal bandwidth and a reduction of 0.2 (not applicable) to support higher data transmission, such as 1 Gbps VCSELs over longer distances.
To meet the ever-increasing demand for bandwidth, the laser-optimized multimode fiber (LOMMF) standards OM3 and OM4 were developed in 2002 and 2009, respectively, with effective modal bandwidths (EMB) of 2000 MHz∙km and 4700 MHz∙km 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 850 nm and 1300 nm (1300 nm LEDs are no longer used for 10G or higher system speeds). However, recently, OM5 (Wideband MMF) was developed and standardized in TIA and ISO/IEC organizations to support short wavelength division multiplexing (SWDM) from 840 nm to 953 nm.
2. Multimode fiber (MMF) reach 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 inherently limited EMB. Let's take a closer look at the potential risks you may face when re-using old OM1 and OM2 fiber optic cables without completing the fiber upgrade.
When used with the newer MMF type (50µm core), the OM1 (62.5µm core) has a different fiber geometry that can cause excessive signal loss even at short distances.
OM1 and OM2 only support very limited reach for 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 (3.0 dB/km); therefore, it may not be possible to meet an appropriate connection budget.
Currently, OM3 and OM4 are the most popular MMF types in modern data centers. OM5 was recently introduced to 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 an older OM3 MMF with a newer bend-insensitive MMF (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 because the latest application standard is developed based on the OM4 specification.
OM5 is backwards compatible with OM4, so it supports an equal scope of current applications. Its main difference is support for transmitting multiple wavelengths on a single MMF thread. When used in conjunction with OM5, SWDM-based transceivers can significantly reduce 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, legacy fiber optic cables can be re-used for new applications (depending on the fiber type), and as long as the capacity of the fiber is not limited, the fiber does not have to be upgraded. However, this is not always the case without full knowledge of the link loss budget and transmission penalty.
When doing network speed upgrades, our suggestion is to replace the old OM1/OM2 or old OM3 with high-quality OM4 BI-MMF cables to prevent light from escaping and causing attenuation caused by bending. This results in better performance, higher bandwidth capabilities and improved optical performance. We also recommend taking a close look at OM5 if you plan to use SWDM-based transceivers in future fiber upgrades.
