OM1 vs OM2 vs OM3 vs OM4 vs OM5 Multimode Fiber Explained

What "OM" Actually Stands For

OM is short for Optical Multimode. The numbering (OM1 through OM5) is defined by ISO/IEC 11801, the international standard for generic cabling in customer premises. Each OM grade specifies a minimum modal bandwidth at certain wavelengths, which determines the maximum distance the fiber can support at a given Ethernet speed. The fiber's physical dimensions, refractive index profile, manufacturing tolerances, and intended light source all factor into the grade.

The TIA-492AAAx series of standards in North America uses the same OM grades. OM1 is TIA-492AAAA, OM2 is AAAB, OM3 is AAAC, OM4 is AAAD, and OM5 is AAAE. Cable manufacturers can list either reference on the print legend; both mean the same thing.

One important point that confuses people new to fiber: the OM grade only describes the multimode glass itself. It says nothing about the cable jacket material, the construction (loose tube vs tight buffered), the fiber count, or the connector. A 12-fiber OM4 indoor riser cable and a 144-fiber OM4 outdoor armored cable use the same glass. For a deeper look at cable construction see our loose tube vs tight buffered guide.

OM1 Through OM5 Side by Side

Modal bandwidth (measured in MHz*km) is the key metric. It tells you how much pulse spreading per kilometer the fiber permits at a given wavelength. Higher modal bandwidth means longer distance for a given data rate. The leap from OM2 (500) to OM3 (2000) is enormous and reflects the shift from LED-driven fiber to laser-optimized fiber.

OM1: 62.5 Micrometer Core, LED-Era Legacy

OM1 has a 62.5 micrometer core, which is the largest of any multimode grade still in use. The large core was a design choice for the LED light sources that dominated 1980s and 1990s fiber optic networking. LEDs spread light across a wide angular cone, and a larger core captured more of that emitted light, improving the link budget. OM1's modal bandwidth at 850 nm is only 200 MHz*km because the large core supports more modes and therefore more modal dispersion.

OM1 is identified by an orange jacket. It works fine for the speeds it was designed for: 10BASE-FL, 100BASE-FX, and 1000BASE-SX over short distances. It cannot support 10GbE at any meaningful distance (33 m is the upper limit), it does not support 40 or 100 GbE at all, and it cannot be retrofitted to higher speeds because the core geometry is wrong for modern VCSEL transceivers.

If you walk into a building constructed before 2005 and find orange multimode patch cords with no aqua/violet/green cable visible, assume it is OM1 until proven otherwise. The only way to confirm is to read the print legend on the cable jacket or test with a known-good 1310 nm source.

OM2: The Bridge to 50 Micrometer

OM2 was the first multimode grade to standardize on the 50/125 micrometer core that all later grades share. The smaller core supports fewer modes and therefore less modal dispersion, which raises modal bandwidth to 500 MHz*km at 850 nm. OM2 still uses an orange jacket, identical to OM1, which is a source of constant confusion in the field.

OM2 supports 10GbE to 82 m, which made it adequate for short data center runs in the early 2000s. It does not support 40 or 100 GbE. OM2 was specified for many enterprise installations between 2000 and 2005 and is still in service in those buildings. Like OM1, it should never be specified for new work.

OM3: Laser-Optimized, Aqua, the First Modern Grade

OM3 is where multimode fiber became compatible with the modern data center. Where OM1 and OM2 were designed for LED light sources, OM3 is laser-optimized for the 850 nm VCSEL (Vertical-Cavity Surface-Emitting Laser) transceivers that drive 10/40/100 GbE. The laser optimization comes from tighter manufacturing control of the refractive index profile across the core, which reduces differential mode delay and dramatically improves modal bandwidth at 850 nm to 2000 MHz*km.

OM3 supports 10GbE to 300 m, 40/100GbE to 100 m, and uses an aqua-colored jacket. It is the de facto baseline for any multimode work performed since around 2005 and remains adequate for most data center applications today. Many enterprises specified OM3 throughout their structured cabling between 2005 and 2015 and are still using it without issue.

If you are evaluating an existing OM3 plant for an upgrade to 25 or 40 GbE, the existing fiber will likely support the new speed at the typical link distances inside a data center. Confirm with an OTDR test and verify channel insertion loss before committing. For OTDR fundamentals see our OTDR basics guide.

OM4: The Current Default for New Installs

OM4 is OM3 with tighter manufacturing tolerances. Same 50/125 core geometry, same laser optimization, same VCSEL compatibility. The difference is that OM4 achieves 4700 MHz*km of modal bandwidth at 850 nm versus 2000 MHz*km for OM3. That higher bandwidth translates directly to longer distance: 400 m at 10 GbE (vs 300 m for OM3), 150 m at 40/100 GbE (vs 100 m for OM3).

OM4 is identified by a violet jacket, sometimes called "Erika violet" or "heather violet" depending on the manufacturer. The price premium over OM3 is small, often only 10-15 percent on bulk cable. Because of the modest price difference and the meaningful distance improvement, OM4 has become the default specification for new multimode installations across enterprise data centers, building backbones, and structured cabling.

If you are pulling new multimode fiber today and have no specific reason to choose otherwise, specify OM4 violet. It will support every current and near-future Ethernet speed at typical building distances.

OM5: Wideband Multimode for SWDM

OM5 is the newest multimode grade, ratified in 2016 as ISO/IEC 11801 wideband multimode (WBMMF). The defining feature is extended modal bandwidth across a wider range of wavelengths from 850 nm to 953 nm, which enables short-wavelength division multiplexing (SWDM). SWDM uses four 25-Gbps wavelengths on a single fiber pair to deliver 100 GbE bidirectionally, or eight wavelengths for 200/400 GbE. This eliminates the need for parallel optics (multiple fiber pairs per link) at higher speeds.

OM5 has the same 50/125 core as OM3 and OM4 and is fully backward compatible with 850 nm VCSEL transceivers. At standard 850 nm operation, OM5 performs identically to OM4 (400 m at 10 GbE, 150 m at 40/100 GbE). The advantage only appears when paired with SWDM transceivers, which extend that distance to 400 m at 100 GbE and add support for higher aggregate speeds.

OM5 uses a lime green jacket. Adoption has been limited because SWDM transceivers remain expensive and most data centers planning multi-hundred-gigabit speeds have moved to single-mode or to parallel optics with breakout cables. Specify OM5 only when you have a documented SWDM roadmap and the transceiver budget to match.

Choosing the Right OM Grade for a New Install

Default: OM4

For nearly every new multimode installation in 2026, OM4 is the right specification. It costs slightly more than OM3, supports longer distances at every speed, and is universally compatible with 850 nm VCSEL transceivers. Building backbones, data center top-of-rack to spine links, and short-reach campus segments all benefit from OM4's headroom.

OM5 only with a confirmed SWDM roadmap

OM5 makes sense when you have a documented plan to deploy SWDM-based 100/200/400 GbE within the cable's expected service life. Without SWDM transceivers, OM5 provides no measurable advantage over OM4 and costs more. The transceiver cost premium for SWDM is significant; budget for that before committing to OM5 cable.

Single-mode if any run exceeds OM4 distance

If any link in your channel exceeds 400 m at 10 GbE or 150 m at 40/100 GbE, you need single-mode. The cable cost is similar but the bandwidth and distance headroom are vastly greater. For mixed environments, designate single-mode for the long backbone segments and OM4 for the short data center links.

Match fiber count to growth plan, not just current need

Pulling fiber is expensive and disruptive. Whatever OM grade you choose, install at least 2x the fiber count you need today. Spare fibers cost very little at the time of install and become invaluable when you need to add capacity, replace a damaged strand, or terminate a new circuit two years later.

Identifying OM Grades in the Field

The fastest way to identify multimode grade is by jacket color. The TIA-598 standard defines:

• Orange jacket: OM1 (62.5 um) or OM2 (50 um). Cannot tell apart by jacket alone; check print legend.
• Aqua jacket: OM3 (50 um, laser-optimized).
• Violet jacket (sometimes called erika violet): OM4 (50 um, higher modal bandwidth).
• Lime green jacket: OM5 (50 um, wideband for SWDM).
• Yellow jacket: Single-mode (OS1, OS2). Not multimode.

For patch cords, the boot color at the connector usually matches the jacket color. If you are auditing an existing cabling plant, walk through and photograph the print legend on every cable jacket; the print includes the manufacturer, the OM grade, the fiber count, and the jacket rating (plenum, riser, OFNR, OFNP). For more on jacket ratings see our plenum vs riser cable guide.

When connecting test equipment, always confirm the OM grade and select the matching launch conditions. An optical power meter typically measures at 850 nm and 1300 nm for multimode work. Verify your meter supports both wavelengths if you are testing legacy OM1/OM2 channels that may use 1300 nm sources.

Patch Cords and Connector Compatibility

All OM grades from OM2 through OM5 use the same 50/125 core geometry, which means patch cords are physically interchangeable between grades. You can plug an OM4 patch cord into an OM3 trunk and the link will function. Mixing grades does cause the channel to perform at the lower grade's specifications, however, so the long OM4 trunk segment ends up limited to OM3's 100 m at 40/100 GbE if any patch cord in the channel is OM3.

OM1 patch cords (62.5 um core) should never be used with OM2-OM5 trunks because the core diameter mismatch causes high insertion loss. The reverse case (OM3+ patch cord into an OM1 trunk) also causes mismatch loss, though slightly less severe. If you have an OM1 plant and need to replace patch cords, source replacement OM1 patch cords specifically.

For multimode patch cords across all grades, we stock LC duplex jumpers and OM4 simplex assemblies in standard lengths. See the OM4 multimode simplex jumper for representative pricing and configurations.

Migration Patterns: Upgrading from Legacy

OM1 plant moving to 10 GbE

OM1's 33 m maximum at 10 GbE makes it impractical for any modern speed beyond Gigabit Ethernet. The realistic options are: pull new fiber (OM4 or single-mode) to the locations that need 10 GbE+, leave the OM1 in place for legacy 1 GbE links until they are decommissioned, or use 1 GbE long-reach optics on OM1 if 10 GbE is not yet required. Trying to push 10 GbE through OM1 over typical building distances will result in unstable links and high bit error rates.

OM3 plant moving to 25 GbE

OM3 supports 25 GbE to 70 m using SR (short reach) optics. Most data center top-of-rack to spine links are well under 70 m and will work with the existing OM3 cabling. For any link that runs longer or needs headroom for future 50/100 GbE, plan a parallel pull of OM4 or single-mode during the next maintenance window.

OM4 plant moving to 400 GbE

400 GbE over multimode requires either SR8 (parallel optics, 8 fiber pairs) or SWDM4 transceivers on OM4 to 100 m, or BiDi/SWDM on OM5 to 150 m. If your OM4 plant uses MPO breakouts already, SR8 is straightforward. If your OM4 plant uses LC duplex throughout, you may need to recable to MPO trunks or accept the distance limit of duplex SWDM on OM4. For an introduction to MPO connectors see our MPO/MTP guide.

Related Reading

• Single-Mode vs Multimode Fiber -- when to choose multimode at all vs going straight to single-mode.
• How to Choose Between Multimode and Singlemode -- decision framework for new installations.
• MPO/MTP Fiber Connector Guide -- the multi-fiber connector you will use for 40/100/400 GbE on multimode.