Single Mode vs Multimode Fiber: Core Size Decides Reach
The two types look similar, use the same connectors and are completely incompatible at the transceiver level. Choosing the wrong one is an expensive mistake.
Quick Answer
| Attribute | Single mode | Multimode |
|---|---|---|
| Core diameter | About 9 micrometres | 50 or 62.5 micrometres |
| Light source | Laser | LED or vertical cavity laser |
| Typical jacket colour | Yellow | Aqua, violet or orange |
| Reach at 10 Gbps | Tens of kilometres | Up to a few hundred metres |
| Cost of cable | Similar | Similar |
| Cost of optics | Higher | Lower |
| Best for | Between buildings, long links | Within a building, data centres |
Distance requirement is the first question. If it is beyond a few hundred metres, single mode is the only practical answer.
Multimode Grades
OM1 and OM2
Older 62.5 and 50 micrometre grades with limited bandwidth. Fine for short legacy links.
OM3
Optimised for laser sources, commonly rated for 300 metres at 10 Gbps.
OM4
Higher bandwidth, typically 400 metres at 10 Gbps and suitable for short distance 40 and 100 Gbps links.
OM5
Wideband grade allowing several wavelengths to be used together, extending the life of multimode in data centres.
Matching Transceivers
- Choose the fiber type first, based on distance.
- Select transceivers for that fiber type and speed.
- Match the connector type, commonly LC duplex.
- Check the polish: single mode often uses angled polish connectors.
- Never join single mode optics to multimode cable or the reverse.
Real-World Applications
- Campus links between buildings on single mode.
- In building backbone and data centre links on multimode.
- Industrial networks where electromagnetic immunity matters.
- Long distance surveillance and sensor networks.
Related Guides
For connectors, read fiber optic connector types. For the basics, see what is fiber optic cable.
FAQ
Which is faster?
Both carry the same speeds. The difference is how far they carry them.
Can I mix them?
No. The optics are matched to the core size, and mixing them results in no link.
Which is cheaper overall?
Multimode costs less at the transceiver end. Single mode wins where distance rules out multimode.
How do I identify the type?
The jacket colour and the printed specification on the cable, for example 9/125 or 50/125.