Generally speaking, there are two types of fibers: those that support multiple propagation paths or transverse modes are called multi-mode fibers (MMF), and those that support a single mode are called single-mode fibers (SMF). But what is the difference between them? Reading this article will help you get the answer.
1. What is single-mode fiber?
In fiber optic communications, a single-mode fiber (SMF) is an optical fiber that directly transmits optical signals in the transverse mode. Single-mode fiber operates at a data rate of 100M/s or 1 G/s, and the transmission distance can reach at least 5 kilometers. Typically, single-mode fiber is used for long-range signal transmission.
2. What is multimode fiber?
Multimode fiber (MMF) is primarily used for short-distance fiber-optic communications, such as in buildings or campuses. The typical transmission speed is 100M/s, the transmission distance can reach 2km (100BASE-FX), 1 G/s can reach 1000m, and 10 G/s can reach 550m. There are two types of indices of refraction: graded index and step index.
3. What is the difference between single-mode fibers and multi-mode fibers?
3.1. Core diameter:
Single-mode fiber: Typical single-mode fibers are 8 and 10 µm core diameter and 125 µm cladding diameter;
Multimode fiber: The usual multimode fiber is 50 and 62.5µm in core diameter and 125µm in cladding diameter;
3.2. Color:
Single-mode fiber: Generally, the color of the fiber jumper is yellow, and the connector and protective sleeve are blue;
Multimode fiber: the color of the fiber patch cord is generally green, and the connector and protective sleeve are beige or black;
3.3. Light source:
Single-mode fiber: using a laser as the light source, the light generated by the laser light source is a single light, which can be precisely controlled and has high power;
Multimode fiber: using LED as the light source, the light generated is relatively scattered;
3.4. Modal dispersion:
Multimode fiber: LED light sources are used in multimode fiber to create a range of wavelengths that propagate at different speeds. This will cause multimodal dispersion, which limits the effective transmission distance of multimode fiber patch cords;
Single-mode fiber: The laser used to drive the single-mode fiber produces a single wavelength of light, so its modal dispersion is smaller than that of multi-mode fiber;
3.5. Bandwidth:
Since multimode fiber has a larger core size than single mode fiber, it supports multiple transmission modes, and the modal dispersion of single mode fiber is smaller than that of multimode fiber. For these reasons, single-mode fiber has a higher bandwidth than multi-mode fiber.
3.6. Price:
Single-mode fiber: The price is lower than that of multi-mode fiber, but the equipment of single-mode fiber is more expensive than that of multi-mode fiber, and the cost is higher than that of dual-mode fiber.
Multi-mode fiber: The price is higher than that of single-mode fiber, and the equipment of multi-mode fiber is cheaper than that of single-mode fiber, so the cost of multi-mode fiber is much lower than that of single-mode fiber.
As mentioned above, the total 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 single-mode fiber systems.
3.7. Transmission distance:
Single-mode fiber: Single-mode fiber operates at a data rate of 100M/s or 1G/s, and the transmission distance can reach at least 5KM. Typically, single-mode fiber is used for long-distance signal transmission;
Multimode fiber: Multimode fiber is primarily used for short-distance fiber-optic communications, such as in buildings or campuses. When the transmission speed is 100M/s, the transmission distance reaches 2km.
Comparison of transmission distance between single-mode fiber and multi-mode fiber
| Fiber Type | 1000Base/1Gb（SX）Ethernet | 1000Base/1Gb（LX）Ethernet | 10Gb Ethernet | 40Gb Ethernet | 100Gb Ethernet |
| OS1/OS2 single mode fiber（1310nm） | 5Km | 20Km | 40Km | 40Km | 80Km |
| OM1 multimode fiber（850nm） | 275m | 550m | 33m | / | / |
| OM2 multimode fiber（850nm） | 550m | 550m | 82m | / | / |
| OM3 multimode fiber（850nm） | 550m | 550m | 300m | 100m | 100m |
| OM4 multimode fiber（850nm） | 550m | 550m | 550m | 150m | 150m |
| OM5 multimode fiber（850nm） | / | / | 550m | 440m | 150m |
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 single-mode 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 optical fibers should not be underestimated.
4. Frequently asked questions about single-mode fiber and multi-mode fiber
4.1. Can single-mode 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.
4.2. Can multi-mode optical modules be used on single-mode fibers?
Multi-mode optical modules cannot be used on single-mode fibers, which will not only cause large losses but may even fail to communicate. Because the single-mode fiber has a small wire diameter and a multi-mode optical module has a large light divergence angle. The longer the transmission distance, the greater the attenuation of the signal. The signal may have been attenuated completely before reaching the transmission distance.
4.3. 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-optical 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.
4.4. Choose single-mode fiber or multi-mode fiber?
When choosing single-mode 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, single-mode fiber is the best choice.
5. Summary
From the above comparison, it can be seen that the application fields of single-mode fiber and multi-mode fiber are different. Among them, single-mode fiber is mainly used in metropolitan area networks and PON, and multi-mode fiber is mainly used in enterprise networks and data centers. You can select single-mode fiber or multi-mode fiber according to the actual wiring requirements.
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