SFP / Transceiver Reference
Transceiver form factors, wavelengths, reach and typical transmit power, with the compatibility facts that decide whether a link comes up.
Result
Transceivers
| Standard | Form factor | Media | Reach | TX power | Notes |
|---|---|---|---|---|---|
| 1000BASE-T | SFP | RJ45 copper | 100 m | - | Copper SFP, higher power draw and latency. |
| 1000BASE-SX | SFP | 850 nm MMF | 550 m (OM2) | -9.5 to -3 dBm | Short reach multimode. |
| 1000BASE-LX | SFP | 1310 nm SMF | 10 km | -9 to -3 dBm | The standard 1G single-mode optic. |
| 1000BASE-EX | SFP | 1310 nm SMF | 40 km | -3 to +2 dBm | Extended reach. |
| 1000BASE-ZX | SFP | 1550 nm SMF | 80 km | 0 to +5 dBm | Long reach; may need an attenuator on short spans. |
| 1000BASE-BX | SFP | BiDi 1310/1490 | 10-40 km | -9 to -3 dBm | Single fiber, paired U and D optics. |
| 10GBASE-SR | SFP+ | 850 nm MMF | 300 m (OM3) | -7.3 to -1 dBm | Datacentre short reach. |
| 10GBASE-LR | SFP+ | 1310 nm SMF | 10 km | -8.2 to +0.5 dBm | The workhorse 10G optic. |
| 10GBASE-ER | SFP+ | 1550 nm SMF | 40 km | -4.7 to +4 dBm | Extended reach 10G. |
| 10GBASE-ZR | SFP+ | 1550 nm SMF | 80 km | 0 to +4 dBm | Non-standard but widely interoperable. |
| 10G BiDi | SFP+ | BiDi 1270/1330 | 10-40 km | -8 to 0 dBm | Halves fiber count on constrained routes. |
| 25GBASE-LR | SFP28 | 1310 nm SMF | 10 km | -10 to -3 dBm | 25G access and fronthaul. |
| 40GBASE-SR4 | QSFP+ | 850 nm MMF ×4 | 150 m | - | MPO-12 parallel optics. |
| 40GBASE-LR4 | QSFP+ | CWDM SMF | 10 km | -7 to +2.3 dBm | Four wavelengths on one pair. |
| 100GBASE-SR4 | QSFP28 | 850 nm MMF ×4 | 100 m | - | MPO-12 datacentre. |
| 100GBASE-LR4 | QSFP28 | CWDM SMF | 10 km | -8.6 to +4.5 dBm | Standard 100G single-mode. |
| GPON OLT B+ | SFP | 1490/1310 | 20 km, 1:32 | +1.5 to +5 dBm | Class B+ PON port optic. |
| XGS-PON N1 | SFP+ | 1577/1270 | 20 km | +2 to +6 dBm | 10G symmetric PON. |
# Read optical levels without a light meter
ethtool -m eth0 # Linux
show interfaces transceiver detail # Cisco IOS
show interfaces diagnostics optics xe-0/0/0 # Junos
/interface ethernet monitor sfp-sfpplus1 once # RouterOSAbout SFP / Transceiver Reference
Choosing a transceiver comes down to form factor, wavelength and reach - and getting any of the three wrong means a link that never comes up, or one that comes up and quietly errors. This is the working reference.
Reading DDM before blaming the fiber
Digital diagnostics (DDM/DOM) report transmit power, receive power, temperature, supply voltage and bias current. Record the receive level at turn-up and you gain a baseline that turns future troubleshooting into arithmetic: a 3 dB drop is a dirty connector or a new splice, a slow decline over months is ageing or water ingress, and zero receive with healthy transmit points at a break or a swapped fiber. A high bias current with falling transmit power means the laser itself is dying.
Vendor coding
Transceivers carry an EEPROM identifying the vendor. Some platforms refuse third-party optics by default, though most allow an override - service unsupported-transceiver on Cisco, and Junos generally accepts them with a warning. Third-party optics are usually identical hardware with different coding; the practical risk is support posture, not function. Always verify DDM readings after fitting one.
Common use cases
- Choosing the right optic for a known span length.
- Diagnosing a link that will not come up between mismatched optics.
- Reading transmit and receive levels to check a fiber has not degraded.
Edge cases and gotchas
- Never look into a live fiber - 1550 nm is invisible and can damage your eye.
- Multimode and single-mode optics are not interchangeable, and a multimode optic on single-mode fiber may partially work, which is worse than failing.