A practical guide
A transceiver may fit in the port and still be wrong for the link. Here we go through the six choices that need to match – from data rate and fibre to range, connector and compatibility.
The short answer
Start with the port and the data rate that the equipment actually supports. Then match fibre class, wavelength, connector, range and encoding. Just because the module fits in the port does not mean it works electrically, optically or in the device's software.
The safest order therefore includes five details: device model and software version, port type, desired speed, installed fibre and actual link length. Also add requirements for temperature class if the module is to be placed outdoors or in an uncontrolled space.
Start with the port and form factor
SFP, SFP+, SFP28, QSFP+ and QSFP28 primarily describe physical and electrical interfaces. They are not free synonyms. SFP is typically used for 1G, SFP+ for 10G and SFP28 for 25G, while QSFP+ and QSFP28 are normally used for 40G and 100G respectively. There are exceptions and multi-speed products, so the port's datasheet governs.
Backward compatibility should never be assumed. An SFP module may sometimes work in an SFP+ port at a lower speed, but only if both hardware and software support it. The same caution applies to breakout and adapters. Always check the platform's compatibility matrix and release notes.
Match data rate and Ethernet standard
Two modules with the same form factor can support different data rates and optical variants. Ensure that both ends are running the same standard and that any FEC setting is compatible. At 25G and 100G Forward Error Correction may be a requirement for certain links, while other optical variants are specified for operation without the same FEC mode.
Avoid selecting a module solely based on the marking 10 km or 100G. The product's full type – for example SR, LR, BiDi or CWDM – says more about the fibre, wavelength and transmission method.
Choose singlemode or multimode
Multimode optics typically operate at 850 nm and are often used for shorter links in data centres and buildings. Singlemode optics usually use wavelengths around 1310 or 1550 nm and are common for longer links, campuses, metropolitan networks and operator networks. The transceiver must match the installed fibre.
Do not mix singlemode optics and multimode cable as a planned solution. The fact that light happens to reach at a bench test does not mean that the link has the correct modal bandwidth, attenuation margin or long-term stability.
Size for actual length and power budget
The specified maximum range is a design class, not a promise for every cable path. Connectors, splices, splitters, muxes, dirt and bends contribute to the attenuation. Calculate the expected loss of the link and compare it with the transceiver's optical power budget with a reasonable operating margin.
Also check the minimum allowable attenuation and maximum receiver power on very short singlemode links with powerful optics. A receiver can be overdriven. Attenuators may be needed, but should be selected based on measurement and datasheet.
Check wavelength and fibre direction
Duplex modules transmit and receive over two separate fibres and often use the same nominal wavelength at both ends. BiDi modules, on the other hand, send two different wavelengths over the same fibre and must be used as a matched pair: the transmit wavelength at one end should correspond to the receive wavelength at the other.
For CWDM and DWDM, the channel number or the exact wavelength must match the passive optical infrastructure. Here, it is not sufficient for the form factor and range to be correct.
Verify connectors, DDM and temperature
LC duplex is common for serial duplex optics, LC simplex for BiDi and MPO/MTP for parallel optics such as SR4 and PSM4. Also check UPC versus APC where relevant; incorrect polishing can cause high reflection and should not be connected.
DDM or DOM provides access to diagnostics such as temperature, supply voltage, laser bias, as well as transmitted and received optical effect. The function is valuable during commissioning and troubleshooting, but read values must be compared with the module's limits. Commercial temperature class is not intended for all outdoor environments.
Order checklist
· Document device model, port designation and software version.
· Specify data rate and desired Ethernet standard.
· Specify fibre class: OS2, OM3, OM4 or OM5.
· Specify link length, number of connectors and splices.
· Specify connector type and whether the link is duplex or simplex.
· Specify requirements for temperature class, DDM and coding.
Frequently asked questions
In some platforms yes, but only if the port explicitly supports 10G mode and the correct module. Check the device documentation.
No. Third-party modules can be coded and quality assured for specific platforms. Compatibility should be verified against the exact device model and software version.
Send the device model, port type, speed, fibre class, connector and distance. A picture of the existing label or DOM printout can reduce lead time.
Next step
Verify the device model, port type, fibre class and link distance. We will check the combination and help you choose the right optics before ordering.