| Characteristic | Multimode | Single-mode |
|---|---|---|
| 10GbE example | 10GBASE-SR | 10GBASE-LR |
| Common fibre | OM3 / OM4 | OS2 / G.652 |
| Typical 10GbE reach | 300 m OM3 / 400 m OM4 with SR | 10 km with LR |
| Core size | Typically 50 µm | Approximately 8–10 µm |
| Common wavelength | 850 nm for SR | 1310 nm for LR |
Multimode fibre
Multimode fibre has a larger core and supports multiple propagation modes. At 10GbE, 850 nm SR optics are commonly paired with OM3 or OM4. The practical reach is limited by modal bandwidth and the optical design.
Single-mode fibre
Single-mode fibre has a much smaller core and is designed for long-distance optical transmission. 10GBASE-LR at 1310 nm is a common 10 km-class Ethernet application. Single-mode plant can also support many longer-reach technologies, subject to the installed fibre specification and optics.
Which should a new site install?
The answer depends on the site's distances, existing fibre estate, equipment and future requirements. If all links are short and the equipment is standardised around SR, OM3/OM4 can be entirely practical. If building-to-building distances are uncertain or future bandwidth is expected to grow, OS2 can provide a longer-lived fibre plant, provided the organisation is comfortable with the appropriate optics and testing.
Do not mix optics casually
An SR optic expects a multimode optical environment; an LR optic is designed for single-mode. Always confirm the transceiver specification, fibre type, connector and optical budget together.