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 and Multi-mode Fiber?
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. Propagation
In digital multimode fiber systems, a light pulse separates into multiple spatial paths or modes. Each component reaches the receiver at a slightly different time, broadening the received pulse. Single-mode fiber solves the differential mode delay problem, allowing data rates to be increased until chromatic dispersion.
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;
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;
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
Singlemode fiber has a lower power loss characteristic than multimode fiber, which means light can travel longer distances through it than it can through multimode fiber.
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. Singlemode VS Multimode Fiber: Advantages and Disadvantages
Singlemode Fiber
Advantages: Least degradation of signals; High bandwidth; Can’t be tapped because of its single path
Disadvantages: High cost; Manufacturing is difficult; Requires a laser source to launch the signal
Multimode Fiber
Advantages: Relatively easy to manufacture; Less expensive; Splicing is easy
Disadvantages: Bandwidth is small; Due to dispersion, data rate is lower and less efficient; Not suitable for long distance communication
5. Singlemode VS Multimode Fiber: How to Choose?
The most important principle is: based on the transmission distance to be covered as well as the overall budget allowed.
If the distance is less than a couple of miles, multimode fiber will work well and transmission system costs (transmitter and receiver) will be in the admissible range.
If the distance to be covered is more than 10–12 miles, single-mode fiber is the choice. Transmission systems designed for use with single-mode fiber will typically cost more (due to the increased cost of the laser diode).
Also, there are other tips for reference.
Single-mode fiber (SMF) provides higher spectral efficiency than multimode fiber (MMF). There is more capacity potential with SMF, as more channels can exist. The higher core size in MMF limits some higher bit rates. That said, both support 100GigE just fine, and the upcoming 400GigE plans. So if by speed, that is your answer.
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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