The Evolution of Multimode Fiber: From OM1 to OM5

Fiber optic technology has been at the heart of modern communications for decades, enabling high-speed data transmission across local area networks (LANs), data centers, and telecommunication systems. While single-mode fiber dominates long-haul networks, multimode fiber (MMF) remains the standard for short- to medium-distance applications due to its lower cost, easier termination, and compatibility with standard transceivers. Over the years, multimode fiber has evolved from OM1 to OM5, each generation improving bandwidth, reach, and application flexibility. This article explores the evolution, technical differences, use cases, and future trends of OM1 through OM5 multimode fibers.

1. Introduction to Multimode Fiber

Multimode fiber (MMF) differs from single-mode fiber primarily in its core size, which is larger (typically 50 or 62.5 microns), allowing multiple light modes to propagate simultaneously. This property simplifies coupling to inexpensive light sources such as vertical-cavity surface-emitting lasers (VCSELs) or LEDs, making MMF ideal for enterprise networks, data centers, and campus deployments.

However, supporting multiple light modes introduces modal dispersion, which limits the maximum distance for high-speed signals. To address this, the International Electrotechnical Commission (IEC) and TIA/EIA developed standardized categories known as OM (Optical Multimode) classes: OM1, OM2, OM3, OM4, and the latest OM5.

2. OM1 – The First Standard Multimode Fiber

OM1 was the original multimode fiber standardized for LANs and early optical networks. Key characteristics include:

• Core diameter: 62.5 µm

• Cladding diameter: 125 µm

• Bandwidth: ~200 MHz·km at 850 nm

• Laser-optimized: No; primarily designed for LED light sources

• Typical reach: 275 m for 1 Gbps, 33 m for 10 Gbps

OM1 fiber was widely used in legacy enterprise networks and early 1 Gbps Ethernet installations. While its performance is adequate for 1 Gbps over short distances, the modal dispersion significantly limits higher-speed applications. Its use today is largely in older infrastructures or where low-cost connectivity is sufficient.

3. OM2 – The Workhorse for 1G and 10G

OM2 emerged as an upgrade to OM1, designed to support higher-speed networks with better bandwidth characteristics:

• Core diameter: 50 µm (smaller than OM1 for improved performance)

• Bandwidth: 500 MHz·km at 850 nm

• Laser-optimized: No, LED-based systems

• Reach for 10G Ethernet: ~82 m

By reducing the core size and improving modal performance, OM2 allowed longer distances for 1 Gbps and 10 Gbps Ethernet. It became the default multimode fiber for many enterprise installations in the late 1990s and early 2000s. However, as 10G Ethernet became more common, laser-optimized fibers became necessary.

4. OM3 – Laser-Optimized Multimode Fiber (LOMMF)

With the advent of 10G, 40G, and 100G Ethernet, traditional LED-based multimode fiber was no longer sufficient. OM3 was introduced as laser-optimized multimode fiber (LOMMF):

• Core diameter: 50 µm

• Bandwidth: 2000 MHz·km at 850 nm (effective modal bandwidth)

• Laser-optimized: Yes, designed for VCSEL lasers

• Typical reach: 300 m for 10G, 100 m for 40/100G Ethernet

OM3 became the preferred fiber for high-speed data centers because it significantly extended reach for 10G/40G/100G networks while maintaining lower cost and easier installation compared to single-mode fiber. Its blue jacket is commonly used to distinguish it from OM4.

5. OM4 – Extended Laser-Optimized Fiber

As data centers demanded even higher speeds and longer distances, OM4 was developed as an improvement over OM3:

• Core diameter: 50 µm

• Bandwidth: 4700 MHz·km at 850 nm

• Laser-optimized: Yes, supports VCSEL lasers

• Typical reach: 400 m for 10G, 150 m for 40/100G Ethernet

OM4 supports higher data rates and longer distances, making it ideal for large data centers, campus networks, and high-density computing environments. Its performance reduces the need for early migration to single-mode fiber, balancing cost and speed. OM4 is often identified by its aqua-colored jacket.

6. OM5 – Wideband Multimode Fiber for the Future

The latest addition, OM5, also known as WBMMF (Wideband Multimode Fiber), was standardized to support emerging technologies:

• Core diameter: 50 µm

• Bandwidth: Same as OM4 but over multiple wavelengths (850–950 nm)

• Laser-optimized: Yes, supports shortwave wavelength division multiplexing (SWDM)

• Typical reach: 100 m for 100G/400G SWDM Ethernet over four wavelengths

OM5 enables multi-wavelength transmission over a single fiber strand, allowing operators to increase bandwidth without installing more fibers. It is highly suitable for high-density data centers and environments where minimizing fiber count is essential. Its lime-green jacket distinguishes it from OM3 and OM4.

7. Comparative Overview of OM1–OM5

8. Key Drivers of Multimode Fiber Evolution

Several factors drove the evolution from OM1 to OM5:

1. Increasing Network Speeds: From 1G Ethernet to 400G Ethernet and beyond, higher bandwidth and lower modal dispersion were required.

2. Cost Efficiency: Multimode fiber provides a lower-cost solution compared to single-mode fiber for short- to medium-range applications.

3. Data Center Density: High-density cabling environments demand fibers capable of supporting higher speeds without massive cable counts.

4. Laser Technology Advances: The development of VCSELs and SWDM enabled multimode fiber to deliver higher speeds over the same strands.

5. Backward Compatibility: Each OM upgrade maintained compatibility with existing infrastructure where possible, easing migration.

9. Applications of OM1–OM5 Fibers

• OM1 & OM2: Small-scale enterprise networks, legacy 1G–10G LAN connections, short-distance intra-building links.

• OM3 & OM4: Modern enterprise LANs, hyperscale data centers, high-speed Ethernet (10G, 40G, 100G), storage area networks (SANs).

• OM5: Future-proof, high-density data centers, SWDM Ethernet, and applications where reducing fiber count and cable management is critical.

10. Future Trends in Multimode Fiber

The multimode fiber landscape continues to evolve:

1. SWDM Adoption: OM5 is the foundation for SWDM, which can quadruple bandwidth over existing fiber.

2. 400G & Beyond: Data centers will increasingly adopt OM5 or high-performance OM4 to meet ultra-high-speed networking needs.

3. Integration with Optical Modules: Transceivers and cables are being optimized for OM4/OM5 to ensure low power consumption and better thermal performance.

4. Migration Strategies: Enterprises are gradually replacing OM1/OM2 with OM3/OM4/OM5 to future-proof networks and improve scalability.

5. Environmental Considerations: LSZH and low-smoke, halogen-free jackets are becoming standard for safety in data centers.

Conclusion

The evolution from OM1 to OM5 represents a journey driven by performance, cost efficiency, and future-ready design. Each successive generation improved bandwidth, reduced modal dispersion, and enabled longer distances for high-speed communication. Today, OM4 and OM5 fibers are the backbone of data centers and high-speed enterprise networks, supporting 10G, 40G, 100G, and beyond, while OM5 introduces multi-wavelength capability for next-generation SWDM networks.

For network designers, system integrators, and fiber optic manufacturers, understanding the differences and applications of each OM class is essential. Investing in OM4 and OM5 deployments today ensures scalability, backward compatibility, and a path toward the ultra-high-speed networks of the future.