25G SFP28 eSR vs LR: Choosing Between Multimode and Single Mode

A 25G SFP28 link can use two common optical modules: the eSR for multimode fiber and the LR for single mode fiber. The right choice usually comes down to two questions. What fiber is already installed, and how far does the link need to run?

The short answer

• Multimode fiber, up to 300 m on OM4: choose the 25G eSR.
• Single mode fiber, up to 10 km: choose the 25G LR.
• Both ends of a link must match. An eSR module belongs with another eSR on multimode fiber. An LR module belongs with another LR on single mode fiber.

25G eSR and LR side by side

Figures come from the Aerless datasheets for each module. Both are Class 1 laser products and RoHS compliant.

Start with the fiber you already have

Most of the decision is already made by the cabling in your building or on your site. Multimode fiber is common inside a data hall or a single building. Single mode fiber is common between buildings, across a campus and on longer runs. Confirm which type you have, and for multimode, whether it is OM3 or OM4, before you choose a module.

Then measure the real run, including patch panels and every connector. The reach in a specification is a maximum under stated conditions. Connectors, splices and the condition of the fiber all reduce what a link can achieve, so leave margin instead of ordering for the longest published distance.

Read the optical numbers

The transmit power range and receiver sensitivity in each datasheet are the inputs to a link budget. Compare them with the measured loss of your own fiber, connectors and splices, and keep margin in reserve. The LR datasheet also lists a dispersion penalty of up to 2.0 dB after 10 km of G.652D single mode fiber.

Power draw differs too. The LR is specified for up to 1.4 W and the eSR for up to 1 W. In a dense switch with many 25G ports, that difference adds to the heat each port contributes.

When the eSR fits

• The link runs over OM3 or OM4 multimode fiber within the stated reach.
• The equipment sits in the same room, building or data hall.
• You need a 25GBASE-SR optic in an industrial temperature range.

When the LR fits

• The link runs over single mode fiber.
• The distance is beyond multimode reach, up to 10 km.
• The link joins buildings, sites or cabinets that are far apart.

Industrial temperature and 5G fronthaul

Both modules are specified for an operating temperature of −40°C to +85°C, which suits cabinets and sites without full climate control. Both support CPRI option 10 and eCPRI applications, so they are candidates for 5G fronthaul links. Confirm the exact CPRI or eCPRI application, fiber type and distance with your equipment documentation before you order.

Check compatibility before you order

Each Aerless module can be programmed to present the vendor code your switch expects. Share your switch model and software version, and we confirm coding before you order. If a module has to be proven in your environment before a wider rollout, we support you through testing and qualification. For a broader view of module families, read our guide to SFP ports and types.

Frequently asked questions

Can I use an eSR module on single mode fiber?

No. The eSR is designed for multimode fiber and the LR for single mode fiber. Use the module that matches the fiber in the link.

Can an eSR connect to an LR across one link?

No. The two modules use different wavelengths and fiber types, so both ends of a link need the same module type.

What reach do the modules support?

The eSR is specified for up to 300 m on OM4 and 200 m on OM3. The LR is specified for up to 10 km on single mode fiber. Actual links depend on the loss of the cabling you install.

Are both modules industrial temperature rated?

Yes. Both are specified for −40°C to +85°C.

What is the lead time?

Lead time is 4 to 6 weeks on all SFPs, including SFP28 modules. We supply customers across the United States and Canada.

Specify your 25G link with Aerless

Aerless is TechFoundry’s hardware business. Our optics and fiber range includes Taiwan manufactured optical transceivers with industrial temperature options. We offer volume based pricing. Contact us to get your price.

Send your switch models, fiber type, distance and quantities, and we will recommend the right module. Request an Aerless optics quote.