In current radio access fronthaul and transport networks, 25G SFP28 remains a common interface rate between AAU/RRU and DU equipment. As site capacity grows and the number of fronthaul links increases, using a dedicated fiber pair for every 25G signal can place increasing pressure on fiber availability and cabling resources.

When fiber resources are limited and multiple 25G fronthaul services need to share the same fiber pair, 25G SFP28 DWDM can carry independent 25G links on different wavelengths, improving utilization of existing fiber infrastructure without requiring large-scale fiber expansion.

However, deploying DWDM in fronthaul networks involves more than selecting a 25G SFP28 module and inserting it into the link. Wavelength planning, MUX/DEMUX insertion loss, optical link budget, receiver type, FEC, host compatibility, and operating temperature all need to be considered together.

This guide reviews the key selection and deployment checks for 25G SFP28 DWDM in 5G fronthaul from a practical engineering perspective.

When Does 5G Fronthaul Need 25G DWDM?

Not every 25G fronthaul link requires DWDM.

If sufficient dedicated fiber is available between sites and the number of links is limited, a conventional 25G single-mode point-to-point solution is often simpler.

DWDM becomes particularly valuable in scenarios such as:

• Multiple 25G fronthaul links need to share limited fiber resources.
• Expanding the existing fiber cable is difficult or adding new fiber is costly.
• Traffic from multiple AAU/RRU links needs to be concentrated toward the DU.
• The fronthaul network already uses DWDM MUX/DEMUX equipment.
• Additional wavelengths and service capacity may be required in future upgrades.

Therefore, the first question when evaluating 25G DWDM is not simply “How far does the transceiver need to reach?” but rather:

DWDM provides its clearest deployment value when fiber count has become a practical bottleneck for network expansion.

25G SFP28 DWDM Wavelength Planning

In a DWDM system, independent 25G links are carried on different wavelengths over the same fiber pair. Wavelength planning is therefore one of the first items that must be confirmed before deployment.

Confirm the DWDM Channel

Fixed-wavelength SFP28 DWDM transceivers are typically assigned to specific DWDM channels. Before deployment, make sure that:

• The transceiver wavelength matches the corresponding channel on the DWDM MUX/DEMUX.
• The modules at both ends of the link use the intended matching wavelength.
• Channel numbering is consistent across the network.
• Sufficient wavelength resources are reserved for future expansion.

If the module wavelength does not match the MUX/DEMUX channel, the host device may still recognize the transceiver correctly, but the optical signal will not pass through the intended DWDM path.

Avoid Duplicate Wavelength Allocation

In a multi-wavelength system, each service link should have a clearly defined wavelength assignment. For example:

This type of mapping reduces confusion during deployment, maintenance, and troubleshooting. For larger fronthaul networks, it is better to establish a unified channel-mapping table during the initial rollout rather than reorganizing wavelength resources later during expansion.

Treat SFP28 DWDM and MUX/DEMUX as One Complete Optical Link

A 25G SFP28 DWDM transceiver does not operate in isolation. A typical DWDM fronthaul path may include:

Compared with a conventional point-to-point 25G optical link, a DWDM system introduces an important additional loss element: MUX/DEMUX insertion loss.

For this reason, nominal transceiver reach alone is not enough to determine whether a link will work.

Two links of the same 2 km fiber length can have significantly different total loss if one is a direct SFP28 connection and the other passes through DWDM MUX/DEMUX devices.

In practical deployment, the MUX/DEMUX, connectors, patch cords, and other passive components must all be included in the optical link budget.

Do Not Rely Only on “2 km” or “10 km” — Calculate the Real Link Budget

The nominal reach of an optical transceiver is useful for initial screening, but it does not replace a link-budget calculation.

After determining the available optical budget, subtract all losses in the actual link. Typical loss sources include:

• Fiber attenuation
• DWDM MUX/DEMUX insertion loss
• Connector loss
• ODF / patch-panel loss
• Splice loss
• Patch-cord loss
• Loss from other passive optical components
• Engineering margin

A practical fronthaul link can therefore be considered as:

The total link loss must remain within the optical budget supported by the selected transceiver.

Why Keep an Engineering Margin?

Field links are not static. Over time, connector contamination, fiber bending, changes in splice performance, temperature variation, equipment aging, or the addition of new ODF and patching points can increase total optical loss.

Keeping an engineering margin at the design stage helps prevent a link that works during initial testing from operating too close to receiver sensitivity limits during long-term service.

PIN or APD? Do Not Choose by Receiver Type Alone

Different 25G SFP28 DWDM products may use either PIN or APD receivers. In general, APD receivers can provide higher receiver sensitivity and are therefore suitable for applications that require a larger optical budget.

However, this does not mean that APD is automatically the better choice for every link.

For shorter fronthaul paths with relatively low link loss, a PIN-based solution may already meet the requirement while offering advantages in power consumption and cost.

A more practical selection sequence is:

1. Calculate the actual link loss.
2. Determine the required link budget.
3. Check the Tx power and receiver sensitivity of the candidate module.
4. Then decide whether PIN or APD is the better fit.

In other words, receiver selection should be based on the complete optical path rather than using receiver type alone as a measure of product capability.

Operating Temperature Matters in Fronthaul Environments

5G fronthaul equipment is not always installed in temperature-controlled data center environments. Optical modules may be deployed in outdoor cabinets, edge sites, base-station equipment cabinets, or non-temperature-controlled telecom rooms.

These environments can experience a much wider temperature range than a typical data center. Module operating temperature therefore needs to be confirmed during product selection.

If the deployment environment has significant temperature variation, industrial-temperature transceivers should be evaluated rather than selecting modules only by rate, wavelength, and reach.

Operating temperature may look like a secondary datasheet parameter, but in fronthaul networks it can directly affect long-term module stability.

25G SFP28 DWDM Deployment Checklist

5. Perform Pre-Deployment Validation

Before volume deployment, validate the complete link in the actual network environment rather than testing the transceiver alone.

Key items include:

• Receive power
• BER
• FEC status
• Link stability
• Temperature
• Alarm information

How to Select the Right 25G SFP28 DWDM Solution

In practical projects, the following logic can be used as a quick selection guide:

For 5G fronthaul, the best solution is not necessarily the optical module with the longest reach.

ETERN Optoelectronics 25G SFP28 DWDM Solutions

ETERN Optoelectronics provides SFP28 DWDM optical transceiver solutions for 25G networks and fronthaul applications. Product selection can be matched to different wavelength, receiver type, transmission distance, and operating-temperature requirements.

For an actual project, module selection should consider the target DWDM channel, MUX/DEMUX parameters, fiber distance, total link loss, and host compatibility together rather than relying only on the nominal transmission distance.

For volume fronthaul deployments, sample validation and compatibility testing on the actual target equipment should be completed before mass production rollout to reduce deployment and maintenance risks.