OM4 is a 50/125μm laser-optimized multimode fiber commonly used for short-reach 10G, 40G, and 100G links in data centers, enterprise backbones, and storage networks. Under IEEE-standardized conditions, OM4 supports up to 400 m for 10GBASE-SR, 150 m for 40GBASE-SR4, and 100 m for 100GBASE-SR4-though actual reach always depends on the transceiver model, connector format, and total link loss.
That last point matters more than most buyers realize. Saying "OM4 supports 100G" is technically correct but incomplete: a 40GBASE-SR4 link does not share the same distance limit as a 100GBASE-SR4 link, and even the same application can perform differently when connector loss, splice quality, or cable grade changes. This guide walks through what OM4 fiber actually delivers, how it compares with OM3, OM5, and single-mode fiber, and how to match the right OM4 cable to your network.
What Is OM4 Fiber?
OM4 is a laser-optimized multimode fiber with a 50 μm core and 125 μm cladding. It is engineered to work with 850 nm VCSEL-based transceivers-the short-wavelength optics used in most data center and enterprise Ethernet applications.
The defining specification is its effective modal bandwidth (EMB). According to the Ethernet Alliance fiber reach reference, OM4 provides a minimum EMB of 4700 MHz·km at 850 nm-more than double the 2000 MHz·km of OM3. That additional bandwidth is what allows OM4 to carry higher data rates over longer distances before modal dispersion degrades the signal.
In practical terms, OM4 lets light signals travel through multiple paths inside the fiber core while maintaining tighter control over pulse spreading than older multimode fiber types such as OM1, OM2, and OM3. The result is a fiber that handles 10G, 40G, and 100G short-reach links with better distance margin.
Key OM4 Fiber Specifications
| Specification | Typical OM4 Value |
|---|---|
| Fiber type | Laser-optimized multimode fiber |
| Core / cladding size | 50/125 μm |
| Primary operating wavelength | 850 nm (also rated at 1300 nm) |
| Minimum EMB at 850 nm | 4700 MHz·km |
| Common jacket color | Aqua or erika violet (varies by region and manufacturer) |
| Common connectors | LC, SC, MPO/MTP |
| Typical applications | Data center interconnects, enterprise backbones, SAN storage links, HPC short-reach connections |
OM4 Fiber Speed and Distance: What Can It Really Support?
OM4 is often promoted as a "10G/40G/100G cable," which is broadly true but hides important differences between Ethernet applications. The only reliable way to evaluate OM4 reach is to look at the specific optical standard and transceiver you plan to deploy.
| Ethernet Application | Connector | Typical OM4 Reach | Source / Notes |
|---|---|---|---|
| 10GBASE-SR | Duplex LC | 400 m (IEEE standardized) | Ethernet Alliance notes IEEE extended 10GbE reach to 400 m on OM4 |
| 40GBASE-SR4 | MPO/MTP (8 fibers) | 150 m | Uses 4×10G parallel lanes; Corning notes 40GBASE-SR4 requires eight OM3/OM4 fibers |
| 100GBASE-SR4 | MPO/MTP (8 fibers) | 100 m | TIA Fiber Optics Technology Consortium lists OM4 operating range up to 100 m |
| 100GBASE-SR10 | MPO/MTP (20 fibers) | Up to 150 m (older 10-lane design) | Less common in new deployments; largely replaced by SR4 |
| 400GBASE-SR4.2 | MPO/MTP (8 fibers) | Up to 100 m | Uses 850 nm PAM4; OM4 still viable for short 400G multimode links |
| 40G/100G BiDi | Duplex LC | Varies by transceiver model | Reuses duplex multimode infrastructure; check vendor datasheet |
Critical point: do not assume every 100G OM4 link can reach 150 m. The 150 m figure comes from older 100GBASE-SR10 references. Most modern 100GBASE-SR4 QSFP28 modules-such as Cisco's QSFP-100G-SR4-S-are specified for 70 m on OM3 and 100 m on OM4 with MPO connectors.
Why 100G Distance Depends on the Transceiver
The phrase "100G over OM4" can refer to very different physical-layer architectures. 40GBASE-SR4 uses four transmit and four receive fibers at 10G per lane. 100GBASE-SR4 also uses four lanes but operates each at 25G, which pushes the fiber's bandwidth harder and reduces the standards-based reach.
A practical example: a network engineer upgrading a data center from 40GBASE-SR4 to 100GBASE-SR4 might expect the same 150 m reach on existing OM4 trunks. But because 100GBASE-SR4 runs at a higher lane rate, the standardized OM4 reach drops to 100 m. If the longest trunk in the facility is 120 m, that link will not meet specifications-even though the same cable worked fine at 40G.
Before buying OM4 cable for any 100G link, confirm the exact transceiver type, the required connector (LC or MPO/MTP), the number of fibers, the maximum supported distance, the allowed insertion loss, and whether the link follows an IEEE standard or a vendor-specific specification.
OM3 vs OM4 Fiber: What Is the Real Difference?
OM3 and OM4 are both laser-optimized 50/125 μm multimode fibers used with 850 nm short-reach optics. They can look identical in the field. The practical difference comes down to bandwidth and the distance margin it buys you.
| Parameter | OM3 | OM4 |
|---|---|---|
| Minimum EMB at 850 nm | 2000 MHz·km | 4700 MHz·km |
| 10GBASE-SR reach | 300 m | 400 m |
| 40GBASE-SR4 reach | 100 m | 150 m |
| 100GBASE-SR4 reach | 70 m | 100 m |
For a 70–100 m 100GBASE-SR4 link inside a data center, OM4 is usually the safer multimode choice because it provides the reach margin that OM3 cannot. If your longest run is 50 m and you have no plans to exceed 10G, OM3 may still serve. But for new high-speed infrastructure where even modest cable-route changes could push a link past OM3 limits, the incremental cost of OM4 is small compared with the cost of re-cabling later.
OM4 vs OM5 vs Single-Mode Fiber
OM4 vs OM5
OM5 is also a 50/125 μm multimode fiber, but it is designed for shortwave wavelength division multiplexing (SWDM) applications that use multiple wavelengths in the 850–953 nm window. OM5 is usually lime green, while OM4 is commonly aqua or erika violet.
Choose OM5 only when your transceiver strategy specifically relies on SWDM to increase capacity over fewer fibers. For the vast majority of standard 10G, 40G, and 100G SR deployments today, OM4 remains the dominant multimode fiber in the field.
OM4 vs Single-Mode Fiber
OS2 single-mode fiber is the better choice for long-distance links, campus backbones, metro-area connections, and projects where you need one cabling platform from the server room to the property line.
OM4 earns its place when links are short (under 100–150 m), when you already invest in multimode SR transceivers, when you need high-density parallel optics inside a data center, and when the cost difference between multimode and single-mode optics matters at scale. Single-mode pulls ahead when link distances grow, when you are building a new backbone expected to serve 400G or 800G in the future, or when your network already standardizes on single-mode optics end to end.
The decision is not binary. Many large campuses use single-mode for building-to-building backbones and OM4 inside each building for short server-to-switch connections.
Quick Decision Guide
| Scenario | Recommended Fiber | Reason |
|---|---|---|
| 10GBASE-SR links up to 400 m | OM4 | Full IEEE-standardized 10G reach on OM4; no need for single-mode optics |
| 40GBASE-SR4 links up to 150 m | OM4 | Well within OM4 parallel-optics limits; uses 8-fiber MPO/MTP |
| 100GBASE-SR4 links up to 100 m | OM4 | Standard SR4 OM4 reach; verify transceiver datasheet |
| Short 400G multimode links (SR4.2) | OM4 (evaluate carefully) | OM4 can support 400GBASE-SR4.2 to ~100 m; confirm with vendor |
| Long campus backbone (>300 m) | OS2 single-mode | Multimode reach is insufficient; single-mode scales to kilometers |
| New long-term backbone build | OS2 single-mode | Future 400G/800G coherent optics require single-mode fiber |
| 10G upgrade to 100G, existing OM4 plant | Reuse OM4 | If runs are ≤100 m, existing OM4 can be reused with 100G SR4 optics |
Common OM4 Fiber Cable Types
OM4 is available in several cable and connector formats. The right selection depends on your equipment ports, pathway routing, fire rating requirements, and cabling architecture.
OM4 Patch Cables
OM4 fiber patch cables connect switches, servers, storage arrays, patch panels, and transceivers. The most common connector for high-density data center environments is the LC duplex, thanks to its small form factor and wide transceiver compatibility. Other combinations-LC-to-SC, SC-to-SC, LC-to-ST-serve legacy or mixed-vendor environments.
If you are buying OM4 patch cables for 100G SR4, the connector interface and polarity matter as much as the fiber grade. A duplex LC patch cable cannot plug into an SR4 QSFP28 module that requires an MPO-12 interface.
OM4 MPO/MTP Trunk Cables
MPO/MTP OM4 trunk cables are the backbone of parallel-optics and high-density structured cabling systems. For 40GBASE-SR4 and 100GBASE-SR4, MPO/MTP connectivity is essential-these applications transmit and receive over multiple fibers simultaneously.
When ordering MPO/MTP OM4 trunks, confirm the fiber count (8, 12, or 24), male or female connector gender, polarity type (Method A/B/C per TIA-568), key-up or key-down orientation, any breakout requirements, and the insertion loss grade (standard or low-loss). Getting even one of these wrong-especially polarity-can result in a cable that physically connects but fails to pass traffic.
OM4 Jacket Ratings: OFNP, OFNR, LSZH, and PVC
| Jacket Type | Typical Application | When Required |
|---|---|---|
| OFNP (Plenum) | Air-handling spaces above drop ceilings, under raised floors | NEC Article 770 plenum requirements; most US commercial buildings |
| OFNR (Riser) | Vertical shafts between floors | NEC riser-rated pathways |
| LSZH | Enclosed spaces where halogen gas is a hazard | European and Asian standards; transit, marine, and tunnel installations |
| PVC | General indoor horizontal runs | Where local code permits general-purpose cable |
Do not choose jacket type by price alone. Building code, project specification, and the physical installation environment should drive the decision. A PVC cable installed in a plenum space violates fire code and can create liability.
How to Choose the Right OM4 Fiber Cable
A sound OM4 selection process starts with the network application, not the cable color or price.
Step 1: Confirm the Data Rate and Transceiver
Identify the exact optical module-10G SFP+ SR, 25G SFP28 SR, 40G QSFP+ SR4, 100G QSFP28 SR4, 100G BiDi, or a vendor-specific optic. The same OM4 cable behaves differently depending on the transceiver's lane rate, wavelength, and fiber count requirement.
Step 2: Measure the Full Channel Distance
Measure end to end: patch cords, trunks, cassettes, adapter panels, and cross-connects. Do not measure only the straight-line distance between two switches. In a structured cabling environment with two patch panels and a trunk, the total channel length is often 10–20 m longer than the trunk alone.
Practical example: a 100GBASE-SR4 link with an 85 m trunk, two 5 m patch cords, and two MPO cassettes totals roughly 95 m of channel. That leaves only 5 m of margin against the 100 m OM4 limit-tight enough that any additional loss could push the link out of specification.
Step 3: Check the Loss Budget
A link can fail even if the distance looks acceptable. Too many connectors, dirty end faces, poor splices, or low-quality cassettes increase insertion loss and eat into the transceiver's optical power budget. Always review connector loss, splice loss, cassette loss, total channel insertion loss, and the transceiver's specified optical budget. In many data center upgrade projects, the link that worked at 10G fails at 100G not because the cable changed, but because the higher lane rate leaves less loss margin.
Step 4: Choose the Connector Type
Use LC duplex for most 10G and 25G links. Use MPO/MTP for parallel-optics applications such as 40GBASE-SR4 and 100GBASE-SR4. If you plan to migrate from 10G duplex LC to 40G or 100G parallel optics, plan the cabling architecture carefully-you may need MPO trunk cables, cassettes, or breakout cables to bridge the two connector worlds.
Step 5: Select the Right Jacket Rating
Choose OFNP, OFNR, LSZH, or PVC according to the installation environment and local code. In the United States, most commercial data center overhead pathways require plenum-rated cable. In Europe and parts of Asia, LSZH is the standard for enclosed environments. Always verify with the project specification or authority having jurisdiction.
Step 6: Request Test Reports
For business-critical links, ask for factory test results showing insertion loss and return loss per connector. For installed links, use optical loss test sets to verify end-to-end channel loss. OTDR testing is useful for locating faults in longer trunk runs but is not a substitute for insertion-loss certification.
Field Example: Choosing OM4 for a 100GBASE-SR4 Data Center Link
A mid-size colocation provider needed to connect a new row of leaf switches to spine switches 80 m away using 100GBASE-SR4. The existing plant was OM3, installed five years earlier. At 80 m, OM3's maximum SR4 reach of 70 m was too short. Rather than replacing the backbone trunk immediately, the team ran new OM4 MPO-12 trunk cables in the existing pathway. The 80 m distance fell well within OM4's 100 m SR4 limit, leaving 20 m of margin for patch cords and cassettes. Factory test reports confirmed insertion loss below the transceiver's specified budget, and the links came up cleanly at 100G on the first attempt.
The takeaway: OM4's additional 30 m of reach over OM3 at 100GBASE-SR4 can be the difference between a working link and a redesign. Always measure the full channel-not just the trunk-before committing to a fiber grade.
OM4 Cable Selection Table
| Application | Typical Distance | Connector | Recommended Cable | Key Consideration |
|---|---|---|---|---|
| 10GBASE-SR server-to-switch | ≤400 m | Duplex LC | OM4 LC-to-LC patch cable | Verify SFP+ module supports OM4 reach |
| 40GBASE-SR4 spine-leaf | ≤150 m | MPO/MTP-12 | OM4 MPO trunk cable | Confirm 8-fiber vs 12-fiber count; check polarity method |
| 100GBASE-SR4 data center backbone | ≤100 m | MPO/MTP-12 | OM4 MPO trunk cable + cassettes or breakout | 100 m limit is strict; account for total channel loss |
| 100G BiDi reusing duplex plant | Varies | Duplex LC | OM4 LC-to-LC patch cable | Check vendor-specific reach on selected BiDi transceiver |
| 400GBASE-SR4.2 short link | ≤100 m | MPO/MTP-12 | OM4 MPO trunk cable | Emerging application; confirm optic compatibility |
| Plenum-rated data center | Any OM4 application | Any | OM4 OFNP-rated cable | Required for air-handling spaces in most US commercial buildings |
FAQ
Q: Can OM4 fiber support 100G?
A: Yes. OM4 supports 100GBASE-SR4 up to 100 m using MPO/MTP connectors and four parallel 25G lanes at 850 nm. It can also support 100G BiDi over duplex LC, depending on the transceiver model. Always verify the reach specification on the specific 100G module you plan to use.
Q: How far can OM4 fiber run?
A: It depends on the application. OM4 reaches 400 m for 10GBASE-SR, 150 m for 40GBASE-SR4, and 100 m for 100GBASE-SR4. These are standards-based distances; actual reach can be shorter if channel insertion loss is high.
Q: Is OM4 single-mode or multimode?
A: OM4 is multimode fiber. It has a 50 μm core that carries multiple light modes. Single-mode fiber (such as OS2) has an approximately 9 μm core and carries a single light mode over much longer distances.
Q: Is OM4 better than OM3?
A: OM4 offers more than twice the effective modal bandwidth of OM3, which translates to longer reach at every major Ethernet speed. For new installations or any link approaching OM3's distance limits, OM4 is the stronger choice. OM3 may still suffice for very short runs in existing plants.
Q: What color is OM4 fiber?
A: OM4 cable jackets are typically aqua or erika violet. However, color is not standardized as a definitive identifier. Always check the cable's printed marking or product datasheet to confirm the fiber grade.
Q: Can OM4 be used for 400G?
A: Yes, in certain short-reach applications. 400GBASE-SR4.2 operates over eight OM4 fibers using 850 nm PAM4 modulation and can reach approximately 100 m. For longer 400G links or coherent 400G transport, single-mode fiber is required.
Before You Order: Final Checklist
Before finalizing an OM4 cable purchase, match the cable to your transceiver datasheet, measure the full channel length (not just the trunk), calculate the insertion loss budget, confirm the connector interface and polarity, verify the jacket fire rating against your building code, and request factory test reports for mission-critical links. Getting these details right upfront avoids costly rework and ensures the link performs as designed from day one.
