Single Mode vs Multimode Fiber, What is The Difference?

In this Article we will help you learn the difference and find out which one best meets your fiber cabling system.

Also will discuss how both Multimode and Single mode fiber compare in terms of:

• Core diameter
• Wavelength
• Bandwidth
• Attenuation
• Color code
• Distance
• Cost
• Application

What is single mode fiber? 

Single mode fiber, short as SMF, is the fiber cable that only allows one mode of light to transmit. Typically, this fiber includes a small light-carrying core of about 9µm diameter. These feature a small modal dispersion for vast-distance signal transmission.

In contrast with multimode fiber, single mode enables the concentration of light for quicker and farther going. That is crucial for high-speed networks over a long distance.

What is multimode fiber?

Unlike single mode, multimode fiber (MMF) allows multiple light modes to transmit and pass through. Typically, this fiber includes a large light-carrying core of about 50µm or 62.5µm diameter. That makes manufacturing easier and offers a lower cost ratio on the same length.

However, due to modal dispersion, this limits the greatest length of transmission connections. So these fibers are mainly for the short-distance transmission of signals.

Commonly multimode fiber can be divided into five types:

• OM1: it has a diameter of 62.5µm and an orange jacket. With 200/500 MHz*km overfilled launch (OFL) bandwidth at 850/1300nm, it is suitable for 100 Megabit and 1G Ethernet applications.
• OM2: it has a diameter of 50µm and an orange jacket. With 200/500 MHz*km overfilled launch (OFL) bandwidth at 850/1300nm, it is suitable for 100 Megabit, 1G, and 10G Ethernet applications.
• OM3: The laser-optimized MMF fiber supports 2000 MHz*km effective modal bandwidth. With a diameter of 50µm and an aqua jacket.
• OM4: A further laser-optimized fiber supports 4700 MHz*km EMB bandwidth. Sutitable for 10 Gb/s, 40 Gb/s, and 100 Gb/s transmissions.
• OM5: also known as WBMMF (wideband multimode fiber), uses two fibers to transfer data at speeds ranging from 40 GB/s, 100 GB/s to 400 GB/s.

Single mode vs multimode fiber, what is the difference?

Now that we have learned their definitions, it is time to compare their difference.

Based on the different factors, we took the below benchmarks into their comparison.

1. Core Diameter

Single-mode and multimode fibers have different physical core dimensions.

The below figure shows the different core diameters comparison.

The core size of single-mode fibers is small, with the most common typical diameter being 9µm, although other sizes are available. It has lower attenuation, supporting higher bandwidths and longer transmission distances.

The multimode core size is much larger, typically 62.5µm or 50µm. Depending on the fiber type, OM1 is 62.5µm in diameter, while OM2/OM3/OM4/OM5 are all 50µm in diameter.

Although there is a clear difference in size, it isn’t easy to see these differences with the naked eye. That is because they are all smaller than the width of human hair. Usually, you can check the printed code on the fiber optic cable to see.

However, if they have a protective cladding, single mode and multimode fibers are 125µm in diameter.

2. Wavelength

Multimode fiber is usually suitable for 850nm and 1300nm short wavelengths. Because it with a large fiber core, the industry can offer the transceiver with lower-cost components like LEDs (light emitting diodes) and VCSELs (vertical cavity surface emitting lasers).

3. Bandwidth

These two types of fibers offer different bandwidths. Let’s make a simple comparison.

Because single-mode fiber optic cable supports a single light source mode, it has lower attenuation and less dispersion. As a result, it can provide a nearly unlimited amount of bandwidth. That makes it the preferred choice for high-speed interconnections over long distances for telecommunications.

However, multimode fiber optic cable can transmit multiple optical modes. Moreover, the attenuation is high, and the dispersion is large. So, it is why its bandwidth is limited.

In this regard, single-mode fiber is the winner.

4. Attenuation

Single mode fiber has lower attenuation than multimode typically. In contrast, Multimode fiber is more vulnerable to attenuation.

Below table list the Attenuation comparison.

5. Color Code

Different color makes us distinguish the cable type easily. TIA-598C defines the suggested color code for the industry.

• Multimode OM1 and OM2 usually have the orange jacket.
• OM3 and OM4 usually have Auqa color jackets.
• OM5 was colored green.
• Single mode OS1 and OS2 typically with Yellow jackets.

6. Distance

Due to the less attenuation and mode dispersion, single mode provides a much longer transmit distance than multimode.

As a result, multimode fiber cabling is only used in the short links (ex. 550m for 1Gbps) while providing low cost. However, Single mode cabling is mainly for very long-reach transmission.

7. Cost

When talking about it, we consider the total cost based on three segments.

7A. Fiber cabling cost

Because of the many advantages of single-mode fiber, many people might think that single-mode cable would be more expensive than multimode cable.

However, the opposite is true. Isn’t that strange?

The reason is that single-mode fiber is more efficient to manufacture, saving an average of 20~30% compared to multimode fiber. If you consider the more expensive OM3/OM4/OM5 fibers, single mode can save about 50% or even more.

However, we must consider another critical cost – the optical transceiver.

7B. Transceiver cost

As an essential segment of fiber cabling, the optical transceiver takes up a large percentage of the cost-sharing. Sometimes, it may share 70% of the total cost.

Single mode transceivers typically cost 1.2~6 times more than multimode. Because single mode usually utilizes a high-power laser diode (LD) that is much more expensive. While multimode devices usually use the lower-cost LED or VCSEL.

7C. System upgrade cost

The dramatic growth in thought drives the cabling system to upgrade and expand. Generally speaking, single mode fiber cabling provides more scalability, flexibility, and elasticity.

Due to the limited bandwidth and short distance, multimode fiber makes it challenging to meet future long-distance and high-volume signal transmission needs.

Plus, for the single mode fiber, you could easily upgrade the system by only changing the switch and transceivers, but you don’t need to lay any new fibers.

For multimode fiber, you will have to replace the OM2 with OM3 and then 0M4 for higher-speed transmission. However, it will cost much more to change the fibers Laying underneath the floor.

To summarize, MMF provides a lower total cost for short distances. Single mode fiber is the best choice for medium to long distances.

8. Application

Given the above comparison, single mode is mainly for long-distance backbone and metro systems in telecom, FTTx, datacom, and CATV networks.

Multimode fiber is mainly for comparatively short-distance applications.

For example, data centers, cloud computing, security systems, and LANs (Local Area Network).