Comparison of single-mode fiber and multi-mode fiber

In today's network construction, optical fiber has been widely used due to its high speed and fast speed. Among them, single-mode fiber and multi-mode fiber are the most common. There are still many questions about the difference and application of these two types of fibers. Next, we will analyze the differences between single-mode fiber and multi-mode fiber in terms of their basic structure, transmission distance, and cost.

1. Comparison of basic structure of single-mode fiber and multi-mode fiber

The basic structure of optical fiber is generally composed of outer sheath, cladding, core, and light source. Single-mode fiber and multi-mode fiber have the following differences:

Color difference of outer sheath

In practical applications, the color of the outer sheath of the fiber can be used to quickly distinguish single-mode fiber from multi-mode fiber. According to the TIA-598C standard definition, single-mode fibers OS1 and OS2 use yellow outer sheaths, multimode fibers OM1 and OM2 use orange outer sheaths, and OM3 and OM4 use aqua blue outer sheaths (for non-military use).

Figure 1: The color of the outer sheath of a single multimode fiber

Core diameter difference

There is a significant difference in core diameter between multi-mode fiber and single-mode fiber. The core diameter of multi-mode fiber is usually 50 or 62.5 µm, and the core diameter of single-mode fiber is 9 µm. In view of this difference, a single-mode fiber can only transmit optical signals with a wavelength of 1310nm or 1550nm on a narrow core diameter, but the advantage of the small core is that the optical signal propagates in a straight line in the single-mode fiber. Refraction occurs, the dispersion is small, and the bandwidth is high; the multimode fiber has a wide core, which can transmit multiple modes at a given operating wavelength, but at the same time, because the multimode fiber transmits hundreds of modes, each mode The propagation constant of the fiber is different from the group rate, so that the bandwidth of the fiber is narrow, the dispersion is large, and the loss is large.

Figure 2: Single multimode fiber core diameter diagram

Note: The standard cladding diameter of most optical fibers is 125um, and the standard outer protective layer diameter is 245um, which does not distinguish between single and multimode.

Difference in light source

The light source usually has two kinds of laser light source and LED light source. Single-mode fiber uses laser light source, and multi-mode fiber uses LED light source.

Figure 3: Single multimode fiber light source diagram

2. Comparison of transmission distance between single-mode fiber and multi-mode fiber

As we all know, single-mode fiber is suitable for long-distance transmission, and multi-mode fiber is suitable for short-distance transmission. The following table shows the specific transmission distances of different types of single-multimode fibers.

Figure 4: Comparison of transmission distance of single-multimode fiber

It can be seen from the chart that at 1G and 10G speeds, the transmission distance of single-mode fiber is much longer than that of multi-mode fiber, so why don't all data centers use single-mode fiber? This is because the construction of the data center focuses on short-distance transmission. In the short-distance transmission environment, the performance of multi-mode fiber and single-mode fiber are the same, but the cost is lower; at the same time, OM3 and OM4 multi-mode fiber can support higher Speed, in the current era of high-speed networks, the demand for multimode optical fiber cannot be underestimated.

Third, the cost comparison of single-mode fiber and multi-mode fiber

As mentioned above, the cost of multi-mode fiber is lower than that of single-mode fiber. This is mainly due to the cost of equipment hardware, such as the cost difference of the light source and the cost difference of the material.

Similarly, the cost difference between a multi-mode fiber system and a single-mode fiber system is similar, and the construction cost of a multi-mode fiber system is lower than that of a single-mode fiber system. Take the FS solution as an example. The cost of a multi-mode transmission system (multi-mode optical modules and jumpers) ranges from 3,300 yuan to 5,300 yuan, while a single-mode transmission system (single-mode optical modules and jumpers) The cost is usually more than 6,700 yuan, and the price difference is more than 1,000 yuan.

Four, single-mode fiber and multi-mode fiber frequently asked questions

1. Can single-mode fiber and multi-mode fiber be mixed?

Normally it is not possible. The transmission modes of single-mode fiber and multi-mode fiber are different. If two fibers are mixed or directly connected together, link loss and line jitter will be caused. However, single-mode and multi-mode links can be connected through single-multimode conversion jumpers.

2. Can multi-mode optical modules be used on single-mode fibers? How about using single-mode optical modules on multimode fibers?

Multi-mode optical modules cannot be used on single-mode optical fibers, which will cause greater loss; single-mode optical modules can be used on multi-mode optical fibers, but optical fiber adapters must be used to convert fiber types. For example, by using optical fiber adapters, 1000BASE-LX single Mode optical modules can run on multimode fibers. Optical fiber adapters can also be used to solve the connection problem between single-mode optical modules and multi-mode optical modules.

3. How to choose single-mode fiber and multi-mode fiber?

In the selection of single-mode fiber and multi-mode fiber, consideration should be given to the actual transmission distance and cost. If the transmission distance is 300-400 meters, multi-mode fiber can be used. If the transmission distance reaches several thousand meters, single-mode fiber is the best choice.

Conclusion

Single-mode fiber and multi-mode fiber have their own advantages. Single-mode fiber systems are mainly used in metropolitan area networks and PON, and multi-mode fiber systems are mainly used in enterprises and data centers. It is important to choose the fiber system that suits you.