OM1, OM2, OM3, OM4, and OM5 are all types of Multimode Fiber (MMF), mainly used for short-distance, high-speed optical transmission, such as:

1. Enterprise LANs
2. Data centers
3. Server rooms
4. Switch interconnections
5. Campus networks

The main differences between them include:

1. Core size
2. Bandwidth capability
3. Supported transmission speed
4. Maximum transmission distance
5. Light source type
6. SWDM support

 

1. Basic Principle of Multimode Fiber

“Multimode” means:
Light can propagate through the fiber core via multiple paths (modes).
Therefore, multimode fiber typically has:

1. Larger core diameter (50μm or 62.5μm)
2. Lower cost
3. Cheaper optical transceivers
4. Suitable for short distances

However, it also suffers from:

1. Modal dispersion
2. Signal distortion over longer distances

Compared with single-mode fiber (OS2):

Multimode Fiber	Single-Mode Fiber
Larger core	Small 9μm core
Multiple light paths	Single light path
Short distance	Long distance
Lower cost	Higher cost

 

2. OM1–OM5 Comparison Table

Type	Core Size	Jacket Color	Light Source	Bandwidth	Typical Applications
OM1	62.5/125μm	Orange	LED	200 MHz·km	Legacy Fast Ethernet/Gigabit
OM2	50/125μm	Orange	LED	500 MHz·km	Gigabit networks
OM3	50/125μm	Aqua	VCSEL Laser	2000 MHz·km	10G/40G data centers
OM4	50/125μm	Aqua/Violet	VCSEL Laser	4700 MHz·km	25G/40G/100G
OM5	50/125μm	Lime Green	VCSEL + SWDM	28000 MHz·km (SWDM)	100G/200G/400G

 

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3. OM1 Fiber

Features

1. Earliest multimode fiber standard
2. 62.5μm core
3. LED light source
4. Higher modal dispersion
5. Lower bandwidth

Typical Transmission Distance

Speed	Maximum Distance
100M	2 km
1G	275 m
10G	33 m

Typical Applications

Historically used in:

1. Old office buildings
2. Campus networks
3. Industrial systems
4. Legacy Ethernet infrastructure

Current Status

OM1 is now largely obsolete because:

1. Not suitable for modern 10G networks
2. Limited upgrade capability
3. Poor compatibility with new high-speed systems

 

4. OM2 Fiber

Features

1. Improved 50μm core
2. Reduced modal dispersion
3. Higher bandwidth than OM1

Typical Distance

Speed	Maximum Distance
1G	550 m
10G	82 m

Typical Applications

Suitable for:

1. Gigabit enterprise networks
2. Building backbones
3. Small server rooms

Current Position

OM2 is considered a transitional product:

1. Adequate for 1G
2. Limited for 10G
3. Rarely used in new deployments

 

5. OM3 Fiber (Most Widely Used)

Features

OM3 marked the beginning of the high-speed multimode era.
Major improvements:

1. Laser-optimized fiber
2. Designed for VCSEL lasers
3. Much higher bandwidth

Typical Distance

Speed	Maximum Distance
10G	300 m
40G	100 m
100G	100 m

Typical Applications

Very common in:

1. Data centers
2. IDC facilities
3. TOR (Top-of-Rack) switch connections
4. Server-to-switch links
5. 10G SR transceivers

Why OM3 Became Popular

1. Lower Cost

Much cheaper than single-mode solutions.

2. Lower Transceiver Cost

SR optical modules cost significantly less than LR modules.

3. Sufficient for Most Data Centers

Typical internal data center distances are:

1. 30m
2. 50m
3. 100m

OM3 is usually sufficient.
 

6. OM4 Fiber

OM4 can be considered:
An enhanced version of OM3

Major Improvement

Higher bandwidth:

1. OM3: 2000 MHz·km
2. OM4: 4700 MHz·km

Distance Improvement

Speed	OM3	OM4
10G	300m	550m
40G	100m	150m
100G	100m	150m

Typical Applications

Suitable for:

1. Large-scale data centers
2. Spine-leaf architectures
3. 100G SR4 links
4. High-density cabling

Why Many New Projects Choose OM4

Because OM4 is more future-ready:

1. Longer transmission distance
2. Better upgrade capability
3. Backward compatible with OM3

Many modern data centers now standardize on OM4.

7. OM5 Fiber (Wideband Multimode Fiber)

OM5 is the latest multimode fiber standard.
Its key advantage is not just distance, but:

Support for SWDM (Short Wavelength Division Multiplexing)

8. Why OM5 is Special

Traditional OM3/OM4:

1. One wavelength per fiber

OM5:

1. Multiple wavelengths on the same fiber
2. Similar to WDM technology

Supported wavelengths include:

1. 850nm
2. 880nm
3. 910nm
4. 940nm

9. Main Advantages of OM5

1. Reduce Fiber Count

For example:
Traditional 100G SR4:

1. Requires 8-fiber MPO

100G SWDM:

1. Requires only duplex LC

This is valuable in high-density data centers.
 

2. Better Support for Future High Speeds

OM5 is mainly designed for:

1. 100G
2. 200G
3. 400G

Especially suitable for:

1. Hyperscale data centers
2. AI clusters
3. High-density switching environments

10. How to Choose

Scenario 1: Enterprise Networks

Recommended:

OM3

Reasons:

1. Cost-effective
2. Good enough for 10G
3. Low transceiver cost

Scenario 2: New Data Centers

Recommended:

OM4

Reasons:

1. Longer reach
2. Better future scalability
3. More suitable for 100G upgrades

Scenario 3: AI / Cloud Computing Infrastructure

Recommended:

OM5

Especially when:

1. SWDM is required
2. Fiber resources are limited
3. High-density cabling is critical

Scenario 4: Legacy Building Upgrades

You may encounter:

OM1 or OM2

Important considerations:

1. Often limited to 1G
2. Very short 10G distance
3. Aging fiber with higher loss

Many engineers recommend directly upgrading to:

1. OM4
2. or OS2 single-mode fiber

11. Compatibility Considerations

1. Can OM3 and OM4 Be Mixed?

Usually:

Yes

Because both are:

1. 50μm fiber
2. VCSEL-compatible

However:
The entire link performs at the lowest grade.
Example:
OM3 + OM4 → overall performance equals OM3.
 

2. Can OM1 Be Mixed with OM2/OM3/OM4?

Not recommended.
Because:

1. OM1 uses 62.5μm core
2. OM2/3/4/5 use 50μm core

This can cause:

1. Coupling loss
2. Mode mismatch
3. Higher bit error rate

 

12. How Multimode Fiber is Used

1. Common Connectors

Most common:

1. LC
2. SC
3. MPO/MTP (40G/100G)

 

2. Common Optical Module Pairings

Fiber Type	Typical Optical Module
OM3/OM4	SR
OM5	SWDM
MPO Fiber	SR4 / SR8

 

3. Typical Network Connection

Example:
Switch ←→ Optical Transceiver ←→ OM4 Patch Cord ←→ Patch Panel ←→ OM4 Trunk Cable ←→ Remote Device

13. Real Industry Usage Today

Fiber Type	Current Status
OM1	Nearly obsolete
OM2	Rare in new deployments
OM3	Still widely used
OM4	Mainstream for new projects
OM5	Used in specialized high-end scenarios

 

14. Future Trends

Many large data centers are gradually moving toward:

OS2 Single-Mode Fiber

Reasons include:

1. Falling single-mode cost
2. Better support for 400G/800G
3. No practical distance limitation
4. Better long-term scalability

However, multimode fiber still has important advantages:

1. Lower short-distance cost
2. Lower SR transceiver power consumption
3. Easier deployment inside data centers