September 30, 2022

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What are differences between single-mode fiber and multi-mode fiber?

6 min read

What are differences between single-mode fibers and multi-mode fibers? 



What are differences between single-mode fiber and multi-mode fiber? 

In the process of rapid development of the network, optical fiber is widely used in the field of optical fiber communication due to its advantages of fast transmission rate and large transmission capacity.

Optical fibers are divided into single-mode fiber and multi-mode fibers according to different optical transmission modes.

Since the geometric and transmission characteristics of these two kinds of fibers are quite different, they also have great differences in practical applications.

Next, this article will introduce the difference and use of singlemode fiber and multi-mode fiber in detail, and guide you to correctly select and use singlemode fiber.


1. The basic structural difference between single-mode fiber and multi-mode fiber

Optical fibers are generally composed of structures such as outer sheath, cladding, core and light source.

As shown below, singlemode fiber and multi-mode fiber have the following differences in the outer jacket, core diameter, and light source:

Outer jacket color difference

singlemode fiber and multi-mode fiber can be quickly distinguished by the color of the outer jacket of the fiber.

According to the definition of TIA-598C standard, the outer jacket color of OS1/OS2 singlemode fiber is yellow, while the outer jacket color of multimode fiber is orange or aqua green, among which OM1/OM2 multimode fiber adopts orange outer jacket, OM3 /OM4 multimode fiber has an aqua-green outer jacket (for non-military use), and OM5 multimode fiber has a green outer jacket.

Figure 1: Color comparison of singlemode fiber and multi-mode fiber outer jacket

Core diameter difference

There are significant differences in core diameter between single-mode and multi-mode fibers.

The core diameter of a singlemode fiber (SMF) is generally 9 μm.

Due to the narrow core, it can only transmit one mode of light at 1310nm, 1550nm and WDM wavelengths.

Because of this, the singlemode fiber has a smaller dispersion and a higher bandwidth.

High, and the core diameter of multimode fiber (MMF) is generally 50/62.5μm, the core is wide, it can transmit multiple modes of light at a given operating wavelength (850nm or 1310nm wavelength), but because of multimode There are hundreds of modes transmitted in optical fibers, and the transmission constants and group rates of each mode are different, resulting in narrow bandwidth, large dispersion and large loss of multimode fibers.

What are differences between single-mode fiber and multi-mode fiber? Figure 2: Comparison of single-mode and multi-mode fiber core diameters

Remarks: The standard cladding diameter of most optical fibers is 125 μm, and the standard outer protective layer diameter is 245 μm, regardless of single-mode multi-mode.

Light source difference

single-mode fiber and multi-mode fibers use different light sources.

single-mode fiber generally use laser light sources, while multi-mode fibers generally use LED light sources.

What are differences between single-mode fiber and multi-mode fiber? Figure 3: Comparison of light sources used in singlemode fiber and multi-mode fiber

Second, the difference between the transmission distance of single-mode fiber and multi-mode fiber
As we all know, single-mode fiber is often used for long-distance transmission, and multi-mode fiber is generally used for short-distance transmission.

Different types of single-mode and multi-mode fiber applications have different transmission distances in different rates of Ethernet, as shown in the following table:

Table 1: Comparison of transmission distance between singlemode fiber and multi-mode fiber

Part of the data comes from FAST (FS)

It can be seen from the table that at 1G and 10G rates, the transmission distance of single-mode fiber is much longer than that of multi-mode fiber, so why not all data centers use single-mode fiber?

This is because the construction of data centers is mainly based on short-distance transmission.

In short-distance transmission applications, the performance of multi-mode fiber and singlemode fiber is the same, but the cost is lower, and OM3/OM4 multi-mode fiber can support higher rates , In today’s high-speed network era, the demand for multi-mode fibers should not be underestimated.

Third, the cost difference between single-mode fiber and multi-mode fiber

As mentioned above, the cost of single-mode fiber is higher than that of multi-mode fiber, which is mainly caused by the difference in the cost of equipment hardware, light source and material.

Likewise, multimode fiber systems are less expensive to build than singlemode fiber systems. 


4. Frequently asked questions about singlemode fiber and multi-mode fiber

1) Can singlemode fiber and multi-mode fiber be mixed?

Because the transmission modes of single-mode fiber and multi-mode fiber are different, the two fibers cannot be directly connected together, otherwise it is easy to cause link loss and line jitter.

But we can use conversion equipment, such as single-to-multimode conversion jumpers (ie, mode adjustment jumpers), to connect single-mode links and multi-mode links.

This article introduces several tools for realizing single-multimode link connection “How to realize the conversion of multi-mode fiber to single-mode fiber? , you can read and understand if you are interested.

 

2) Can multi-mode optical modules be used on single-mode fiber?

Multi-mode optical modules cannot be used on single-mode fiber, which will not only cause large losses, but may even fail to communicate.

Because the diameter of the singlemode fiber is small and the light divergence angle of the multi-mode optical module is large, the longer the transmission distance, the greater the attenuation of the signal, and the signal may be attenuated before reaching the transmission distance.

3) Can single-mode optical modules be used on multi-mode fibers?

Single-mode optical modules can be used on multimode fiber, but a fiber-to-fiber transceiver needs to be used to convert the fiber type.

For example, by using fiber-optic transceivers, 1000BASE-LX single-mode optical modules can operate on multimode fiber, as shown in the figure below.

Fiber optic transceivers can also be used to solve connection problems between single-mode optical modules and multi-mode optical modules.

4) How to choose singlemode fiber and multi-mode fiber?

When choosing singlemode fiber and multi-mode fiber, we should consider the actual transmission distance and cost of the network.

If the transmission distance is not more than 550 meters, multi-mode fiber can be used.

If the transmission distance is more than several thousand meters, singlemode fiber is the best choice.


Epilogue

From the above comparison, it can be seen that the application fields of singlemode fiber and multi-mode fiber are different.

Among them, singlemode fiber is mainly used in metropolitan area network and PON, and multi-mode fiber is mainly used in enterprise network and data center, and the selection can be determined according to the actual wiring requirements.



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