This is how you choose the right fibre
Singlemode and multimode suit different environments. The right choice is determined not only by the distance but also by optics, cable route, future capacity, number of connections and total cost over time.
The difference in practice
Singlemode fibre has a smaller core and primarily carries a single light path. It is used with singlemode optics and is suitable for both short and very long links. Multimode fibre has a larger core and can carry multiple light paths simultaneously. It is commonly used with 850 nm optics for short, cost-effective links in data centres and buildings.
View the choice as a system decision. Transceivers, permanent fibre, patch cables, connectors and cassettes need to work together – both for today’s speed and the next upgrade.
OS2: the standard choice for singlemode in many new installations
OS2 is a common class for singlemode cabling in telecoms, campuses, city networks, industry and data centres. The low attenuation and absence of multimodal bandwidth limitation means that the same fibre infrastructure can support many optical systems over time. However, the range is still determined by transceivers, wavelength, dispersion and the link’s power budget.
Singlemode often means a higher cost for optics than short-distance multimode, but provides great flexibility when distance or future capacity is uncertain. Therefore, compare total cost of ownership, not just the price of the patch cable.
OM3, OM4 and OM5: multimode for short high-speed links
OM3 and OM4 are laser-optimised multimode fibres for high data rates. OM4 has a higher specified modal bandwidth than OM3 and can therefore provide greater range for certain Ethernet variants. Exact maximum length depends on the standard, transceiver, and the channel's construction.
OM5 is wideband multimode and designed for transmission over a broader wavelength range. It may be relevant for solutions that use short wavelength multiplexing, but does not automatically provide longer range for standard 850 nm optics. If the application does not utilise OM5's features, OM4 may be a more rational choice.
Five questions that determine the choice
- How long is the longest channel, including patch cables and spare length?
- What speeds are needed today and within five to ten years?
- Is there installed fibre that should be reused?
- Is the lowest initial cost or greatest upgrade freedom the most important?
- What optics are supported by switches, routers, and servers?
Avoid mixing without a technical plan
OM3, OM4, and OM5 have the same nominal core diameter and can be physically connected, but the channel's performance is limited by the weakest part and by splice and connector conditions. Older OM1/OM2 should be treated particularly as core diameter and bandwidth can create additional limitations.
Do not mix APC and UPC-polished connectors. APC is often recognised by a green connector and UPC by blue, but colour is a help – not a substitute for labelling and documentation.
Recommendation per environment
- Data centres with short, standardised links: compare OM4 with singlemode based on transceiver price, density, and upgrade plan.
- Campus, operator, city networks, and longer building connections: OS2 is usually the robust starting point.
- Existing multimode: verify fibre class, length and connector losses before upgrading.
- New installation with unknown future speed: calculate for both optics and cable systems over the entire lifespan.
Yes, if the transceiver's minimum and maximum levels are respected. Check the receiver's overload limit.
No. The value depends on the application and the optics. For many common 850 nm links, OM5 offers no automatic advantage.
Colours are used for identification, but marking, documentation and measurement are safer than colour assessment.
Next step
Are you planning a new link or an upgrade? Send speed, distance and existing fibre. We will help you match fibre, patch cables and transceivers.
See OS2 singlemode patch cables