Single-Mode vs Multimode SFP Wiki and Guide
Single-mode vs multimode fiber is a hot topic in the optical telecom industry. How about single-mode vs multimode SFP, What is single-mode and multimode SFP? How to identify between the two? Does it feasible to use single-mode SFP with multimode fiber and vice versa? Find answers in this post.
What is Single-Mode vs Multimode SFP?
Single-mode and multimode SFP are two SFP transceiver types breakdown by the fiber optic cable worked with them. The single-mode SFP (SMF) refers to SFP that is used with single-mode fibers, while multimode SFP (MMF) means SFP optic that should be used together with multimode fiber patch cables.
Difference Between Single-Mode vs Multimode SFP
Both single-mode SFP and multimode SFP are compact small form-factor pluggable ones. They are quite identical at first sight. So how to identify single-mode and multimode SFP? Here are some tips.
Outer Appearance Identification - Single-Mode vs Multimode SFP Color Coding
Single-mode SFP vs multimode SFP is color-coded with different Bale Clasp. Though the color-coding rule is not total conformity for different vendors, generally the Bale Clasp of multimode SFP is black, and fiber patch cables used with multimode SFP are usually orange (OM1/OM2), aqua green (OM3/OM4), green (OM5).
Fig 1: Black color-coded Bale Clasp 1G SFP are multimode SFP, and used with OM1/OM2 multimode fiber patch cables in orange, OM3, OM4 in aqua green, or OM5 in green.
The most common color of single-mode SFP Bale Clasp is blue, there are also some in yellow, red, etc. Fiber optic jumpers used with single-mode optical modules are generally yellow.
Fig 2: Blue/Yellow/Red color-coded Bale Clasp 1G SFP are single-mode SFP, and are often used with single-mode fiber patch cables in yellow.
Inner Component Identification - Single-Mode vs Multimode SFP Transmitter
The optical module is mainly composed of three parts: optoelectronic device, functional circuit, and optical interface. The transmitter and receiver are two parts of the optoelectronic device, of which the transmitter is the core component of SFP modules.
In the market, VCSEL lasers are the most commonly used multimode optical modules transmitter for short-range optical fiber transmission. And FP (Fabry-Perot) or DFB（Distributed Feedback）lasers are usually utilized in single-mode optical modules for medium to long-distance transmission. VSCEL lasers own the advantages in the production process for they can be tested the whole manufacturing process. The difference between FP and DFB lasers is mainly in semiconductor materials and resonant cavity structures.
DFB has a higher production cost and is designed for high-speed and long-range transmission.
Here are examples of QSFPTEK manufactured SFP modules with different transmitters for different transmission applications.
• Cisco SFP-10G-SR Compatible 10GBASE-SR SFP+ is equipped with a VCSEL transmitter for max 300m short-distance transmission.
• Cisco GLC-LH-SM Compatible 1000BASE-LX/LH SFP is equipped with an FP transmitter for up to 10km long-distance transmission.
• Cisco QSFP-40G-LR4 Compatible 40GBASE-LR4 QSFP+ is equipped with DFB transmitters for up to 10km long-distance transmission.
• Cisco QSFP-100G-ZR4-S Compatible 100GBASE-ZR4 QSFP28 is equipped with EML transmitters for up to 80km long-distance transmission.
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 Price
In general, buying a single-mode SFP costs more than a multimode SFP. As the manufacturing cost is different, mainly lying in the transmitter. Multimode SFP with VSCEL transmitter is cheaper than single-mode SFP with FP/DFB or even EML lasers. You can check the single-mode vs multimode SFP price on QSFPTEK Website.
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.
Conclusion
Single-mode vs multimode SFP refers to SFP module type breakdown by the fiber optic cable worked with them. How to identify single-mode and multimode SFP? An easy and quick way is to distinguish the color of the SFP module Bale Clasp. SFP with black color-coded Bale Clasp stands for multimode SFP, while SFP Bale Clasp in blue, yellow, red refers to single-mode SFP. Other major differences between the two SFP module types are transmitter type, working central wavelength, max transmission distance, single-mode vs multimode SFP price, etc. For the topic of mixed-use of single-mode SFP with multimode fiber, it is feasible for urgent use but not reliable. For multimode SFP with single-mode fiber, remember not to do so, it is a matter of principle and technology. Finally, for achieving the best connection performance the author strongly recommends using single-mode SFP with single-mode fiber and multi-mode SFP with multimode fiber.
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