In today's network construction, optical fiber has been widely used due to its high rate and speed, among which single-mode optical fiber and multi-mode optical fiber are the most common. There are still many questions about the difference and application of these two types of optical fiber. Next, we will deeply analyze the difference between single-mode optical fiber and multi-mode optical fiber from the aspects of their basic structure, transmission distance, cost, etc.

1. Comparison of the basic structures of single-mode optical fiber and multi-mode optical fiber

The basic structure of optical fiber generally consists of an outer sheath, cladding, core, and light source. There are the following differences between single-mode optical fiber and multi-mode optical fiber:

Difference in outer sheath color

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

Difference in core diameter

Multimode fiber and single-mode fiber have obvious differences in core diameter. The core diameter of multimode fiber is usually 50 or 62.5µm, and the core diameter of single-mode fiber is 9µm. In view of this difference, single-mode fiber can only transmit optical signals with a wavelength of 1310nm or 1550nm on a narrower core diameter, but the advantage of a small core is that the optical signal propagates in a straight line in a single-mode fiber without refraction, with less dispersion and high bandwidth; multimode fiber has a wide core, and it can transmit multiple modes at a given working wavelength, but at the same time, because there are hundreds of modes transmitted in a multimode fiber, the propagation constants and group velocities of each mode are different, which makes the bandwidth of the fiber narrow, the dispersion large, and the loss large.

Note: The standard cladding diameter of most optical fibers is 125um, and the standard outer protective layer diameter is 245um, regardless of single mode or multimode.

Differences in light sources

Light sources usually include laser light sources and LED light sources. Single-mode optical fiber uses laser light sources, while multi-mode optical fiber uses LED light sources.

2. Comparison of transmission distances of 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-mode and multi-mode fibers.

At 1G and 10G rates, the transmission distance of single-mode fiber is much longer than that of multi-mode fiber, so why don't data centers use single-mode fiber? This is because data centers are mainly built for short-distance transmission. In short-distance transmission environments, the performance of multi-mode fiber is the same as that of single-mode fiber, but the cost is lower; at the same time, OM3 and OM4 multi-mode fibers can support higher rates. In the current high-speed network era, the demand for multi-mode fiber cannot be underestimated.

3. Cost comparison between single-mode fiber and multi-mode fiber

It is mentioned above that 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 light source and material.

The cost difference between multimode fiber systems and single-mode fiber systems is similar. The cost of building a multimode fiber system is lower than that of a single-mode system. Taking 3Coptics' solution as an example, the cost of a multimode transmission system (multimode optical modules and jumpers) ranges from 3,300 yuan to 5,300 yuan, while the cost of a single-mode transmission system (single-mode optical modules and jumpers) usually exceeds 6,700 yuan, with a price difference of more than 1,000 yuan.

4. FAQs about single-mode and multi-mode optical fibers

1. Can single-mode and multi-mode optical fibers be used together?

Generally speaking, no. Single-mode fiber and multi-mode fiber have different transmission modes. If the two fibers are mixed or directly connected together, it will cause link loss and line jitter. However, single-mode and multi-mode links can be connected through a single-to-multimode conversion jumper.

2. Can I use multimode optical modules on single-mode optical fibers? How about using single-mode optical modules on multimode optical fibers?

Multimode optical modules cannot be used on single-mode optical fibers, which will cause large losses; single-mode optical modules can be used on multimode optical fibers, but a fiber adapter must be used to convert the fiber type. For example, by using a fiber adapter, a 1000BASE-LX single-mode optical module can run on a multimode optical fiber. Fiber adapters can also be used to solve the connection problem between single-mode optical modules and multimode optical modules.

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

When choosing between single-mode fiber and multi-mode fiber, the actual transmission distance and cost should be considered. 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 each have their own advantages. Single-mode fiber systems are mainly used in metropolitan area networks and PONs, while multi-mode fiber systems are mainly used in enterprises and data centers. It is crucial to choose a fiber system that suits you.