10G SFP+ Selection Guide: Choosing Between SR, LR, ER and ZR

The short answer

For 10G SFP+, reach class is determined almost entirely by distance, and wavelength follows from the fiber type you already have:

| Reach class | Wavelength | Fiber | Typical distance | Reference standard | |---|---|---|---|---| | SR | 850 nm | Multimode (OM3/OM4) | Up to 300 m | 10GBASE-SR | | IR | 1310 nm | Single-mode | Up to 2 km | 10GBASE-IR | | LR | 1310 nm | Single-mode | Up to 10 km | 10GBASE-LR | | ER | 1310 / 1550 nm | Single-mode | Up to 40 km | 10GBASE-ER | | ZR | 1550 nm | Single-mode | Up to 80 km | 10GBASE-ZR |

A four-step selection method

Step 1 — Measure the link, not the building. Use the actual cable run length plus a margin for routing and patch panels, then pick the class one step above your need. Buying ER for a 400 m run wastes money; buying LR for a 12 km run simply will not work.

Step 2 — Check the fiber you already own. If it is multimode, SR is the only option in this table and your maximum realistic distance is a few hundred metres. If it is single-mode, IR through ZR are all open to you.

Step 3 — Confirm the equipment's port type and coding. A 10G SFP+ port is a 10G SFP+ port, but some platforms require specific EEPROM coding to accept a third-party module. Confirm this before ordering in volume.

Step 4 — Check the optical budget. For long-reach classes, the link budget — transmit power minus receiver sensitivity, minus connector and splice losses — is what determines whether the link actually comes up. The specification tables on our product pages list Tx minimum, Tx maximum and Rx sensitivity for every part number so you can calculate this directly.

Common mistakes

• Choosing SFP+ ZR for a run that also passes through an optical add/drop multiplexer without accounting for its insertion loss.
• Mixing SR and LR modules at the two ends of the same link. The wavelengths do not match and the link will not come up.
• Assuming all 10G ports support all 10G speeds — some legacy line cards do not support ZR-class optics.

When 1.25G SFP is still the right answer

Not every link needs 10G. Management ports, legacy telecom interfaces and low-bandwidth industrial links are frequently better served by a 1.25G SFP, which costs less and consumes less power. Our SFP series covers 155M to 2.5G with duplex, BiDi and CWDM/DWDM options.