Choosing between single-mode and multimode fiber is one of the first decisions in any optical network project. It affects which transceivers you can use, how far your links can reach and how easily the network can grow. Here is what you need to know.
The core difference
Optical fiber carries light through a very thin glass core. The size of that core defines the type of fiber:
- Single-mode (OS1/OS2): a core of about 9 microns. Light travels in a single path, which minimizes dispersion and allows transmission over many kilometers.
- Multimode (OM1 to OM5): a core of 50 or 62.5 microns. Light travels in multiple paths (modes), which limits the distance but works very well over short runs.
Distance
This is usually the deciding factor. Single-mode fiber supports links from a few meters to 40, 80 km or more, which makes it the standard for ISPs, FTTx networks, campus backbones and connections between buildings. Multimode fiber is designed for distances of up to a few hundred meters. For example, at 10 Gbps an OM3 fiber reaches about 300 m and OM4 about 400 m; at 100 Gbps those distances drop to around 70 m and 100 m.
Multimode categories
- OM1 and OM2: legacy fibers, usually with an orange jacket. Not recommended for new installations.
- OM3: optimized for 850 nm lasers, aqua jacket. A solid choice for 10G.
- OM4: greater bandwidth and reach than OM3. The most popular option in today’s data centers.
- OM5: wideband multimode, lime green jacket, designed for short-wavelength multiplexing.
Cost
Historically, multimode systems were cheaper because 850 nm transceivers cost less than single-mode lasers. Today the price gap between optics has narrowed considerably, and single-mode cable itself is often less expensive than OM4. For short links inside a data center, multimode is still very cost-effective. For anything that may grow in distance or speed, single-mode is the safer long-term investment.
Bend-insensitive fiber
In FTTH installations and tight spaces, fibers are often bent around corners and inside boxes. Bend-insensitive single-mode fibers, such as G.657A1 and G.657A2, keep losses low even with small bend radii. They are the preferred choice for drop cables and indoor deployments.
Golden rule: never mix types
Single-mode and multimode fibers are not interchangeable. The transceivers, patch cords and connectors in a link must all match the same fiber type. Mixing them causes very high losses or a link that simply won’t come up.
So, which one should you choose?
- Choose multimode for short links inside a data center or a telecom room, where 850 nm optics keep costs low.
- Choose single-mode for ISP and FTTx networks, connections between buildings, long backbones, or whenever you want maximum room to grow.
Find the right fiber for your project
Explore our single-mode cables, multimode cables and fiber patch cords. If you are not sure which option fits your installation, talk to our team.