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How do I know if my SFP module is single-mode or multimode?
Knowledge Base + 2024.01.05

There are a few ways to determine if your SFP module is single-mode or multimode:

1. Labeling: Check the labeling on the SFP module. It should indicate whether it is single-mode or multimode.

2. Color: Single-mode and multimode SFP modules often have different colored housings. Single-mode modules are typically yellow, while multimode modules are usually orange or beige.

3. Transmission distance: Single-mode modules are generally designed for longer transmission distances, while multimode modules are intended for shorter distances. Check the specifications of the SFP module to see what distance it is designed for.

4. Use case: Consider the intended use case of the SFP module. Single-mode modules are typically used for long-haul, high-speed communication, while multimode modules are commonly used for shorter distance, lower speed connections.

By considering these factors, you should be able to determine whether your SFP module is single-mode or multimode.

Specifications & Functionalities

Single-Mode vs Multimode SFP Wavelength

The most central wavelength of multimode SFP is 850nm for short-range transmission. Also, some SFP designed for middle-distance (2km as typical) applications uses the 1310nm wavelength. The single-mode optical modules have a more flexible working central wavelength range, common in 1310nm and 1550nm.

Single-Mode vs Multimode SFP Distance

The application of the SFP module is linked with its working wavelength. As mentioned above, multimode SFP works mainly in 850nm wavelength, which is ideal for short-distance transmission. However, the max distance of the 850nm wavelength MMF SFP module varies with the data rates, ranging from 100m (eg. Cisco Compatible SFP-25G-SR-S, QSFP-100G-SR4-S), 150m (eg. Cisco Compatible QSFP-40G-SR4), 300m (such as Cisco Compatible SFP-10G-SR), 550m (eg. Cisco Compatible MGBSX1). Besides, some multimode SFP working in 1310nm wavelength can deliver data up to 20km.

Single-mode SFP can be divided into 10km, 20km, 40km, 80km, 100km, 120km, and more by distance. Taking 10G SFP+ as an example, Cisco Compatible SFP-10G-LR in 1310nm is for 10km, Cisco Compatible SFP-10G-ER in 1550nm is for 40km, and Cisco Compatible SFP-10G-ZR in 1550nm is for 80km. You can distinguish the max distance from the model name.

Single-Mode vs Multimode SFP Hot Topic Discussion

Previously we've pointed out that single mode vs multimode SFP stands for the single-mode or multimode fiber optic cables used together with the SFP. The author found that questions about interconnection have aroused a heated debate in some forums – Will single-mode SFP work with multimode fiber? Can you use single-mode fiber with multimode SFP? In the following paragraphs, the author will explain views on this topic.

Single-Mode SFP with Multimode Fiber

Can I use single-mode SFP with a multimode cable? My answer is - YES. Single-mode SFP works with multimode fiber for short-range transmission within 100 meters. However, it should be treated as a solution of a last resort.

In principle, it is feasible. To understand this point, you need to dive into the difference between single-mode and multimode fiber.

First, identify the light source of single-mode vs multimode fiber. Interfaces that use multimode fiber generally use LEDs as light sources, while interfaces using single-mode fiber uses Laser as the light source.

Second, distinguish the fiber core diameter of single-mode vs multimode fiber. Single-mode fiber has a very narrow fiber core - 9um/7um/5um, while multimode fiber has a wide fiber core - 62.5um (OM1)/50um (OM2/OM3/OM4/OM5).

Third, get to know the transmission mode of single-mode vs multimode fiber. The transmission mode of single-mode fiber is along the axis of the fiber core, which avoids dispersion and power loss. The transmission mode of multimode fiber is refraction. The light signal will be continuously reflected along the edge wall of the fiber core, hence there is a lot of dispersion and waste of light energy.

The fiber core diameter of the multi-mode patch cable is wide, so it is conditioned to connect the light source to this very wide fiber core, but the transmission is not far due to the multimode fiber transmission mode.

As for the real-life experience, our expert has done corresponding tests in the lab. Used product portfolios are 2× Cisco GLC-LH-SM Compatible 1000BASE-LX/LH SFP, 1× 100m OM3 MMF fiber patch cable, and 2× Cisco SG110 gigabit switch. The result shows it's indeed feasible to use single-mode SFP with multimode fiber in short-range transmission. However, due to the characteristics of the multi-mode fiber, it is not recommended to use this method for transmission in long-distance applications. One should judge based on the actual situation. Here are real feedbacks by other users in the Spiceworks community: power loss, CRC fails and link flapping, etc. If it is an extremely urgent situation, such as the degree of fire burning eyebrows, you can try, maybe it can adapt to your short-term emergency.

Multimode SFP with Single-Mode Fiber

Can I use a multimode transceiver with single-mode fiber? My answer is – it is possible but not recommended. We do see the green light when connecting multimode SFP with single-mode fiber, but technically here are some issues.

As we mentioned above, the fiber core diameter of the single-mode patch cable is very narrow. Besides, the LED light source of the multi-mode module is very divergently. Hence when we use single-mode fiber with multimode SFP, only a fraction of the signal emitted by LED should get into the narrow single-mode fiber core. Meanwhile, great signal loss, attenuation, and serious modal dispersion also occur when it enters the single-mode fiber core.

This is why I do not recommend you to do so. Irregular use is always risky, which will lead to uncertain fault. I bet you don't want to live with the anxiety that the link may fail at any time every day, especially for commercial use in SMB, enterprise, and data centers. If you do need to interconnect multimode SFP with single-mode fiber, a more secure solution is to use mode conditioning patch cables or single-mode to multimode media converters.