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Single Mode vs Multimode Fiber: What’s the Difference?

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John

Posted on March 22, 2017
December 5, 2020
138247

Although single mode fiber (SMF) and multimode fiber cable (MMF) are widely used in diverse applications, the problem about differences between single mode fiber and multimode fiber is still confusing. Therefore, the following article will focus on the basic construction, fiber distance, cost, fiber color, etc., to make an in-depth comparison between single mode and multimode fiber.

Overview of Single Mode vs Multimode Fiber

Single mode means the fiber enables one type of light mode to be propagated at a time. While multimode means the fiber can propagate multiple modes. The differences between single mode and multimode fiber mainly lies in fiber core diameter, wavelength & light source, bandwidth, color sheath, distance and cost.

Core Diameter

Single mode fiber core diameter is much smaller than multimode fiber. Its typical core diameter is 9 µm even if there are others available. And multimode fiber core diameter is 50 µm and 62.5 µm typically, which enables it to have higher "light gathering" ability and simplify connections. The cladding diameter of single mode and multimode fiber is 125 µm.

Figure 1 Optical Fiber Core Diameters.png

The attenuation of multimode fiber is higher than SM fiber because of its larger core diameter. The fiber core of single mode cable is very narrow, so the light that passes through these fiber optical cables is not reflected too many times, which keeps the attenuation to a minimum.

9/125 Single Mode Fiber Simplex 50/125 OM3 Multimode Fiber
Attenuation at 1310nm 0.36 dB/km Attenuation at 850 nm 3.0 dB/km
Attenuation at 1550nm 0.22 dB/km Attenuation at 1300 nm 1.0 dB/km

Wavelength & Light Source

Due to the large core size of multimode fiber, some low-cost light sources like LEDs (light-emitting diodes) and VCSELs (vertical cavity surface-emitting lasers) that works at the 850nm and 1300nm wavelength are used in multimode fiber cables. While the single mode fiber often uses a laser or laser diodes to produce light injected into the cable. And the commonly used single mode fiber wavelength is 1310 nm and 1550 nm.

Bandwidth

Multimode fiber bandwidth is limited by its light mode and the maximum bandwidth at present is 28000MHz*km of OM5 fiber. While single mode fiber bandwidth is unlimited theoretically because it allows only one light mode to pass through at a time.

Color Sheath

According to the TIA-598C standard definition, for non-military applications, single mode cable is coated with yellow outer sheath, and multimode fiber is coated with orange or aqua jacket. Find more details about the Fiber Optic Cable Color Code here.

Figure 2 Color Sheath of SMF and MMF.jpg

Single Mode vs Multimode Fiber Distance

It’s known that single mode fiber is suitable for long-distance applications, while multimode optical fiber is designed for short-distance runs. Then when it comes to single mode vs multimode fiber distance, what’s the quantifiable differences?

Fiber Optic Cable Type Fiber Cable Distance

Fast Ethernet 100BA SE-FX 1Gb Ethernet 1000BASE-SX 1Gb Ethernet 1000BA SE-LX 10Gb Base SE-SR 25Gb Base SR-S 40Gb Base SR4 100Gb Base SR10
Single mode fiber OS2 200m 5,000m 5,000m 10km / / /
Multimode fiber OM1 200m 275m 550m (mode conditioning patch cable required) / / / /
OM2 200m 550m / / / /
OM3 200m 550m 300m 70m 100m 100m
OM4 200m 550m 400m 100m 150m 150m
OM5 200m 550m 300m 100m 400m 400m

From the chart, we can see that single mode fiber distance is much longer than that of multimode fiber cables at the data rate from 1G to 10G, but OM3/OM4/OM5 multimode fiber supports a higher data rate. Because multimode optical fiber has a large core size and supports more than one light mode, its fiber distance is limited by modal dispersion which is a common phenomenon in multimode step-index fiber. While single mode fiber is not. That’s the essential difference between them. In addition, OS2 single mode fiber could support longer distances in 40G and 100G links, which is not listed in the table.

Single Mode vs Multimode Fiber Cost

“Single mode vs multimode fiber cost” is a hot topic in some forums. Numbers of people have expressed their own opinions. Their views mainly focus on the optical transceiver cost, system cost and installation cost.

Optical Transceiver Cost

Compared to single-mode transceivers, the price of multimode transceivers is nearly two or three times lower. The following table takes FS.COM Cisco compatible single-mode transceivers and multimode transceivers as an example.

Speed Transceiver Transceiver Description Price Price Difference
1G Single mode SFP Cisco GLC-LH-SMD Compatible 1000BASE-LX/LH SFP 1310nm 10km DOM Transceiver US$ 7.00 US$ 1.00
Multimode SFP Cisco GLC-SX-MMD Compatible 1000BASE-SX SFP 850nm 550m DOM Transceiver US$ 6.00
10G Single mode SFP+ Cisco SFP-10G-LR Compatible 10GBASE-LR SFP+ 1310nm 10km DOM Transceiver US$ 24.00 US$ 6.00
Multimode SFP+ Cisco SFP-10G-SR Compatible 10GBASE-SR SFP+ 850nm 300m DOM Transceiver US$ 24.00
25G Single mode SFP28 Cisco SFP-25G-LR-S Compatible 1310nm 10km US$ 59.00 US$ 20.00
Multimode SFP28 Cisco SFP-25G-SR-S Compatible 850nm 100m US$ 39.00
40G Single mode QSFP+ Cisco QSFP-40G-LR4 Compatible 40GBASE-LR4 and OTU3 QSFP+ 1310nm 10km LC DOM Transceiver US$ 279.00 US$ 240.00
Multimode QSFP+ Cisco QSFP-40G-SR4 Compatible 40GBASE-SR4 QSFP+ 850nm 150m MTP/MPO DOM Transceiver US$ 39.00
100G Single mode QSFP28 QSFP28 Cisco QSFP-100G-LR4-S 100GBASE-LR4 1310nm 10km Compatible Transceiver US$ 499.00 US$ 400.00
Multimode QSFP28 QSFP28 Cisco QSFP-100G-SR4-S Compatible 100GBASE-SR4 850nm 100m Transceiver US$ 99.00

From the table, we can see that the price difference gains greatly with the speed increasing.

System Cost

To utilize the fundamental attributes of single mode fibers, which are generally geared towards longer distance applications, requires transceivers with lasers that operate at longer wavelengths with smaller spot-size and generally narrower spectral width. These transceiver characteristics combined with the need for higher-precision alignment and tighter connector tolerances to smaller core diameters result in significantly higher transceiver costs and overall higher interconnect costs for single mode fiber interconnects.

Figure 3 System Cost.png

Fabrication methods for VCSEL based transceivers that are optimized for use with multimode fibers are more easily manufactured into array devices and are lower cost than equivalent single-mode transceivers. Despite the use of multiple fiber lanes and multi-transceivers arrays, there are significant cost savings over single-mode technology employing single or multichannel operation over simplex-duplex connectivity. Multimode fiber system offers the lowest system cost and upgrade path to 100G for standard-based premises applications using parallel-optic based interconnects.

Installation Cost

Single-mode optical fiber often costs less than multimode fiber. When building a 1G fiber optic network that you want to be able to go to 10G or faster on eventually, the savings on cost of fiber for single-mode saves about half-price. While the multimode OM3 or OM4 fiber increases 35% in cost for SFP modules. The single-mode optics are more expensive, but the labor costs of replacing the multimode are significantly higher, especially if that followed OM1—OM2—OM3—OM4. If you are willing to look at used ex-Fibre Channel SFPs, the price of single-mode 1G drops through the floor. If you have the budget and need for 10G short connections, the economics at last check still support multimode. Keep an eye on those economics though, as history suggests that the price premium for single-mode will drop.

Frequently Asked Question about Single Mode vs Multimode Fiber

Q: What is better single mode or multimode fiber?

A: As has mentioned above, single mode fiber and multimode fiber cable have their own advantages on cost and applications. There is no such thing that single mode optical fibers are better than multimode ones. Just choosing the best-fit one for your applications is ok.

Q: Can I mix single mode and multimode fiber?

A: This answer for this question is “no”. Multimode fiber and single mode fiber have different core sizes, and the number of light modes that they transmit is also different. If you mix the two fibers, or connect them together directly, you’ll lose a large amount of optical loss, resulting in a link flapping or being down. Keep in mind that never mix different types of cabling randomly.

Q: Can I use a multimode transceiver on single mode fiber?

A: Generally speaking, the answer is "no". Large optical loss will occur if a multimode transceiver is connected with single mode fiber. However, the opposite will work. For example, 1000BASE-LX single mode SFP can work on multimode fiber cable by using mode conditioning fiber cable. Sometimes, fiber media converters also can be used to solve such problems between single mode transceivers and multimode transceivers.

Q: Single mode vs multimode Fiber: which should I choose?

A: When making a decision between single mode and multimode fiber cables, the first factor to consider is the fiber distance which you need actually. For example, in a data center, multimode fiber cables are enough for the distance of 300-400 meters. While in applications that require distance up to several thousands of meters, the single mode fiber is the best choice. And in applications that can use single mode and multimode fiber, other factors like cost and future upgrade requirements should be taken into consideration for your choice.

Summary

From the comparison—single mode vs multimode fiber, it can conclude that both single-mode optics and multimode optics have their own features. Single-mode fiber cabling system is suitable for long-reach data transmission applications and widely deployed in carrier networks, MANs and PONs. Multimode fiber cabling system has a shorter reach and is widely deployed in enterprise, data centers and LANs. No matter which one you choose, on the basis of total fiber cost, choosing the one that best suits your network demands is an important task for every network designer.

Related Article:

Single Mode Fiber: How Much Do You Know?

Multimode Fiber Types: OM1 vs OM2 vs OM3 vs OM4 vs OM5