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Fiber optic technology has transformed how data moves inside enterprise LANs, campus networks, and hyperscale data centers. Within fiber optics, multimode fiber (MMF) remains one of the most widely deployed transmission media for short-distance, high-bandwidth connections.
But not all multimode fiber is the same. The industry has developed five standardized categories: OM1, OM2, OM3, OM4, and OM5. Each generation brings improvements in core size, bandwidth, wavelength support, and maximum transmission distance.
This guide will walk through the differences between OM1–OM5 multimode fibers, their physical specifications, Ethernet support, connectors, and advantages. By the end, you’ll know exactly which MMF standard best fits your project.
What is Multimode Fiber?
Multimode Fiber Basics
Multimode fiber has a larger core diameter (50μm or 62.5μm) than single-mode fiber (9μm). This allows multiple light modes to propagate simultaneously. Key properties:
- Core sizes: 50/125μm or 62.5/125μm.
- Light sources: LED (older standards) or VCSEL (Vertical Cavity Surface Emitting Laser) for higher speeds.
- Distance: Optimized for short- to medium-distance (tens to hundreds of meters).
- Cost: Lower than single-mode due to cheaper optics and simpler installation.
Multimode vs Single-Mode Fiber
| Feature | Multimode Fiber (OM1–OM5) | Single-Mode Fiber |
| Core Size | 50–62.5 μm | 9 μm |
| Light Source | LED or VCSEL | Laser |
| Distance | Short (up to ~550m @ 10G) | Long (up to 100 km+) |
| Bandwidth | Up to 28,000 MHz·km (OM5) | Virtually unlimited |
| Cost | Lower | Higher (optics + install) |
OM1 Fiber Characteristics
- Core Diameter: 62.5 μm.
- Outer Jacket: Orange.
- Light Source: LED.
- Bandwidth: 200/500 MHz·km (850/1300 nm).
- Applications: Fast Ethernet (100 Mbps), early Gigabit Ethernet.
Advantages: Good bend resistance, large core for easier alignment.
Limitations: Cannot support modern >10G applications effectively.
OM2 Fiber Characteristics
- Core Diameter: 50 μm.
- Outer Jacket: Orange.
- Light Source: LED.
- Bandwidth: 500 MHz·km.
- Applications: Gigabit Ethernet, limited 10GbE.
Advantages: Reduced modal dispersion vs OM1, lower production cost.
Limitations: Not optimized for high-speed laser-based transmission.
OM3 Fiber Characteristics
- Core Diameter: 50 μm.
- Outer Jacket: Aqua.
- Light Source: Laser-optimized (VCSEL at 850 nm).
- Bandwidth: 2000 MHz·km.
- Applications: 10GbE up to 300m, 40G/100G up to 100m.
Advantages: Major leap forward with laser optimization.
Limitations: Limited to shorter reach at 40G/100G.
OM4 Fiber Characteristics
- Core Diameter: 50 μm.
- Outer Jacket: Aqua.
- Light Source: VCSEL.
- Bandwidth: 4700 MHz·km.
- Applications: 10GbE up to 550m, 40G/100G up to 150m.
Advantages: Backward compatible with OM3, but doubles reach for 10/40/100G Ethernet.
Limitations: Higher cost than OM3, but now standard in modern data centers.
OM5 Fiber Characteristics
- Core Diameter: 50 μm.
- Outer Jacket: Lime Green.
- Light Source: VCSEL with wideband wavelength support (850–953 nm).
- Bandwidth: 28,000 MHz·km.
- Applications: 100G/400G/1T Ethernet, optimized for SWDM (shortwave wavelength division multiplexing).
Advantages: Supports multiple wavelengths on one fiber, reducing fiber count in 100G+ links.
Limitations: Newest standard → higher cost, still early adoption.
Physical Differences Between OM1–OM5
| Fiber Type | Core Diameter | Outer Sheath Color | Optical Source | Bandwidth (MHz·km) |
| OM1 | 62.5 μm | Orange | LED | 200 |
| OM2 | 50 μm | Orange | LED | 500 |
| OM3 | 50 μm | Aqua | VCSEL | 2000 |
| OM4 | 50 μm | Aqua | VCSEL | 4700 |
| OM5 | 50 μm | Lime Green | VCSEL (SWDM) | 28,000 |
Application Differences in Ethernet Standards
| Fiber Type | Fast Ethernet | 1G Ethernet | 10G Ethernet | 40G Ethernet | 100G Ethernet |
| OM1 | 2000m | 275m | 33m | – | – |
| OM2 | 2000m | 550m | 82m | – | – |
| OM3 | 2000m | 550m | 300m | 100m | 100m |
| OM4 | 2000m | 550m | 550m | 150m | 150m |
| OM5 | – | – | 550m | 440m | 150m |
Multimode Fiber Connectors and Compatibility
Common connector types used with multimode fibers:
- LC (Lucent Connector): Small form factor, dominant in SFP/QSFP modules.
- SC (Subscriber Connector): Larger, push-pull style, legacy networks.
- FC (Ferrule Connector): Screw-on type, mostly telecom.
- ST (Straight Tip): Twist-lock, older LAN deployments.
- MTP/MPO: Multi-fiber push-on connectors, essential for 40G/100G parallel optics.
| Connector Type | Ferrule Size | Typical Loss (dB) | Use Case |
| SC | 2.5mm | 0.25–0.5 | Routers, older LANs |
| LC | 1.25mm | 0.25–0.5 | Data centers, SFPs |
| FC | 2.5mm | 0.25–0.5 | Telecom ODFs |
| ST | 2.5mm | 0.25–0.5 | Legacy LANs |
| MTP/MPO | Multi-fiber | 0.25–0.5 | High-speed parallel optics |
Advantages of Multimode Fiber
- Lower Cost: Cheaper than single-mode optics.
- Ease of Installation: Larger core simplifies alignment and splicing.
- Short-Distance Efficiency: Perfect for data centers and campus networks.
- Protocol Support: Works with Ethernet, InfiniBand, Fibre Channel.
- Scalability: OM5 extends MMF into 100G/400G/1T territory.
FAQ: Multimode Fiber Questions
Q1: What is the difference between OM3 and OM4 fiber?
A: OM4 has higher bandwidth (4700 MHz·km vs 2000) and supports longer distances at 10/40/100G.
Q2: Is OM5 backward compatible with OM4?
A: Yes, OM5 shares the same 50 μm core and can be used with OM4 hardware.
Q3: Can multimode fiber replace single-mode fiber?
A: No. MMF is limited to short distances due to dispersion; SMF is required for long-haul.
Q4: Which multimode fiber is best for 100G/400G Ethernet?
A: OM5 is optimized for high-speed parallel optics and SWDM, making it the best choice.
Q5: What connector types are used with multimode fiber?
A: LC and MTP/MPO dominate in modern data centers, while SC and ST are common in legacy networks.
Conclusion
Over three decades, multimode fiber has evolved from OM1 (62.5 μm, LED) to OM5 (50 μm, wideband VCSEL). Each generation reflects the growing bandwidth needs of Ethernet:
- OM1/OM2 → legacy Fast/Gigabit Ethernet.
- OM3/OM4 → modern 10/40/100G data centers.
- OM5 → future-proof for 100G/400G/1T at lower cost than single-mode.
For organizations planning their next network upgrade, choosing the right multimode standard ensures reliable, scalable, and cost-effective connectivity.
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