By Dustin Guttadauro, Product Line Manager - Telecom & Fiber, Infinite Electronics
When a data center network requires multimode fiber, the next question is often OM3 vs OM4 vs OM5: which fiber grade should you choose? All three are 50/125 µm multimode fiber categories designed for high-speed optical networking, but they are not identical. Their bandwidth specifications, supported link distances, and suitability for different optical technologies vary.
For many conventional 850 nm Ethernet applications, OM4 provides a useful performance step above OM3. OM5 was developed as wideband multimode fiber (WBMMF) to support multiple wavelengths and technologies such as shortwave wavelength-division multiplexing (SWDM). However, OM5 does not automatically provide additional reach over OM4 when conventional 850 nm optics are used. That makes fiber selection less about choosing the newest specification and more about matching the fiber, transceiver, data rate, and required distance.
Key Takeaways
- OM3, OM4, and OM5 are 50/125 µm multimode fiber categories.
- OM4 has a higher minimum effective modal bandwidth than OM3 at 850 nm.
- OM5 maintains OM4-level 850 nm bandwidth while adding wideband multimode characteristics for additional wavelengths.
- For 10GBASE-SR, commonly specified maximum distances are 300 m for OM3 and 400 m for OM4/OM5.
- For 40GBASE-SR4, commonly specified distances are 100 m for OM3 and 150 m for OM4/OM5.
- For 100GBASE-SR4, commonly specified distances are 100 m for OM3 and 150 m for OM4/OM5.
- OM5 does not automatically provide greater distance than OM4 when conventional 850 nm SR4 optics are used.
- OM5 becomes more relevant when the optical architecture uses multiple wavelengths, such as SWDM.
- OM4 is often a practical specification for new conventional multimode data center deployments, subject to project requirements.
- OM3 can remain appropriate for existing infrastructure and applications that fit its distance and bandwidth requirements.
- Fiber selection should always be matched to the transceiver, data rate, connector, polarity, and link-loss budget.
- Jacket color can help identify fiber, but cable markings and documentation should be used for definitive identification.
What are OM3, OM4, and OM5 Fibers?
OM3, OM4, and OM5 are categories of multimode optical fiber. All three use a nominal 50 µm core and 125 µm cladding, but their performance specifications differ. The key specification is effective modal bandwidth (EMB).
For conventional 850 nm operation:
- OM3 has a minimum EMB of approximately 2,000 MHz·km.
- OM4 has a minimum EMB of approximately 4,700 MHz·km.
- OM5 has a minimum EMB of approximately 4,700 MHz·km at 850 nm.
OM5 additionally has a specified bandwidth characteristic at 953 nm to support wideband multimode applications. In simple terms, OM4 provides more bandwidth performance than OM3, while OM5 builds on OM4-level 850 nm performance and adds characteristics intended for multi-wavelength transmission.
OM3 Fiber: Where Does It Fit?
OM3 is a laser-optimized 50/125 µm multimode fiber designed for high-speed networking. Its 850 nm effective modal bandwidth is specified at a minimum of 2,000 MHz·km. For 10GBASE-SR, OM3 can support a maximum standardized link length of approximately 300 meters under the relevant specifications. For 40GBASE-SR4, the commonly specified maximum is 100 meters.
OM3 can therefore make sense when:
- Existing infrastructure is OM3.
- Link distances are comfortably within OM3 specifications.
- The network uses compatible 850 nm optics.
- There is no requirement for the additional reach provided by OM4.
- Project economics favor retaining or deploying OM3.
For a new installation, however, engineers should consider the expected life of the infrastructure rather than comparing cable prices alone.
OM4 Fiber: The Higher-Bandwidth Multimode Option
OM4 is also a 50/125 µm multimode fiber but provides a higher minimum effective modal bandwidth than OM3. At 850 nm, OM4 has a minimum EMB of approximately 4,700 MHz·km, compared with 2,000 MHz·km for OM3. That additional bandwidth can translate into greater supported distances for certain high-speed applications.
For example, commonly specified distances include:
- 10GBASE-SR: up to 400 m
- 40GBASE-SR4: up to 150 m
- 100GBASE-SR4: up to 150 m
These values should always be checked against the specific optical transceiver and cabling system being deployed. OM4 is often considered when:
- Designing a new enterprise data center.
- Supporting higher-speed multimode links.
- Additional reach is useful.
- The project requires more performance headroom than OM3.
- The network is expected to migrate toward higher data rates.
OM5 Fiber: What Makes It Different?
OM5 is a wideband multimode fiber designed to support multiple wavelengths within the multimode operating window. Unlike OM3 and OM4, which are primarily specified for operation around 850 nm, OM5 has specifications at both 850 nm and 953 nm. Corning lists minimum EMB values of 4,700 MHz·km at 850 nm and 2,470 MHz·km at 953 nm.
The purpose is to support technologies that use multiple wavelengths over multimode fiber, such as SWDM. This distinction is important:
OM5 is not simply OM4 with more distance. When conventional 850 nm SR4 optics are used, OM5 does not automatically provide more reach than OM4. Both meet the same 4,700 MHz·km minimum EMB specification at 850 nm. OM5 becomes more interesting when the optical architecture actually takes advantage of multiple wavelengths.
Why Does OM5 Exist?
The development of OM5 was driven partly by the need to support multiple wavelengths over multimode fiber. Traditional multimode Ethernet applications often use an optical wavelength around 850 nm. SWDM changes the approach by transmitting multiple wavelengths over the same fiber.
For example, a 40G SWDM system can use four wavelengths to create an aggregate 40 Gb/s connection. This can potentially increase the amount of data transmitted over a fiber without requiring the same number of parallel fibers used by some parallel-optics architectures.
Corning's published technical data gives example 40G SWDM distances of approximately:
- OM3: 240 m
- OM4: 350 m
- OM5: 440 m
For 100G SWDM, the corresponding figures are approximately:
- OM3: 75 m
- OM4: 100 m
- OM5: 150 m
These figures are associated with specific SWDM implementations and should not be treated as universal distances for every transceiver.
OM3 vs OM4: Which Should You Choose?
For engineers comparing OM3 vs OM4, the decision is often more straightforward than the OM4 vs OM5 decision. OM3 can be appropriate where:
- Existing OM3 infrastructure is already installed.
- Link distances are comfortably within OM3 specifications.
- The network speed and optical modules are compatible.
- The project does not require additional OM4 reach.
OM4 may be considered where:
- Higher-speed applications are planned.
- Additional distance margin is valuable.
- New data center infrastructure is being installed
- The network requires up to 150 m for certain 40G/100G SR4 applications
- Additional bandwidth headroom is desirable
For many new multimode installations, the decision should be based on the complete network roadmap rather than the initial cable price.
What About Jacket Colors?
Color conventions can help technicians identify fiber categories, but they should not be the only method used to identify fiber.
Common conventions include:
- OM3: Aqua
- OM4: Aqua
- OM5: Lime green
Because OM3 and OM4 can both use aqua-colored jackets, technicians should rely on cable markings, labels, and documentation to identify the exact fiber grade. The cable jacket color should be treated as a visual aid rather than the definitive specification.
Choosing the Right Fiber Optic Cable Assembly
Once the fiber grade is selected, the next step is choosing the appropriate fiber optic cable assembly.
Verify:
- OM3, OM4, or OM5 fiber
- Fiber count
- Connector type
- Connector gender
- Polarity
- Cable length
- Jacket construction
- Required insertion-loss performance
- Transceiver compatibility
For high-density deployments, engineers may also need to consider MPO trunks, fan-outs, and other multi-fiber configurations. L-com's fiber optic cable assemblies include different multimode configurations for networking applications.
L-com Data Center Fiber Solutions
Once the fiber grade and optical architecture have been established, the next step is specifying compatible connectivity. L-com provides connectivity products for data center applications, including fiber optic cable assemblies and connectors.
Frequently Asked Questions (FAQs)
1. Is OM4 better than OM3?
OM4 provides higher specified effective modal bandwidth than OM3, approximately 4,700 MHz·km compared with 2,000 MHz·km at 850 nm. It also supports longer standardized distances for several high-speed applications. Whether that additional performance is useful depends on the network's data rate and required link distance.
2. What is the difference between OM4 and OM5?
OM4 is optimized primarily around conventional 850 nm multimode applications. OM5 maintains OM4-level bandwidth at 850 nm while adding wideband characteristics designed to support multiple wavelengths, including applications such as SWDM.
3. Does OM5 provide more distance than OM4?
Not automatically. When conventional 850 nm SR4 optics are used, OM5 does not provide more reach than OM4 because both meet the same 4,700 MHz·km minimum effective modal bandwidth at 850 nm. OM5 becomes more relevant when the optical architecture uses multiple wavelengths, such as SWDM.
4. What distances do OM3, OM4, and OM5 support?
For 10GBASE-SR, commonly specified maximum distances are 300 m for OM3 and 400 m for OM4 and OM5. For 40GBASE-SR4 and 100GBASE-SR4, they are 100 m for OM3 and 150 m for OM4 and OM5. These values should always be checked against the specific transceiver and cabling system being deployed.
5. Can I identify OM3, OM4, and OM5 fiber by jacket color?
Jacket color can help, but it should not be the only method. OM3 and OM4 can both use aqua jackets, and OM5 commonly uses lime green. Cable markings, labels, and documentation should be used to identify the exact fiber grade.