What is the difference between single-mode fiber and multi-mode fiber?

Fiber optics are flexible, transparent fibers made of extruded glass or plastic, slightly thicker than a human hair.  Optical fiber is the most common means of transmitting light at both ends and is widely used in optical fiber communication.  Optical fiber has a longer transmission distance and higher bandwidth than cable.  Optical fibers are usually composed of transparent core with low refractive index and transparent cladding material.  As a light wave conductor, optical fiber causes total reflection of light in the fiber core.  

Generally speaking, there are two types of optical fiber: the fiber that supports multiple propagation paths or transverse modes is called multi-mode fiber (MMF), while the fiber that supports a single mode is called single-mode fiber (SMF). But what is the difference between them? Reading this article will help you get the answer.

What is single-mode optical fiber?

In optical fiber communication, single-mode fiber (SMF) is an optical fiber that directly transmits optical signals in 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 km. In general, single-mode fiber is used for remote signal transmission.

Single mode (stage refractive index)

What is multi-mode fiber?

Multi-mode fiber (MMF) is mainly used for optical fiber communication over short distances, such as in buildings or campus. The typical transmission speed is 100M/s, the transmission distance can be up to 2km(100Base-FX),1 G/s can be up to 1000m, and 10 G/s can be up to 550m. There are two types of refractive index: gradient index and step index.

Multimode (graded refractive index)

What is the difference between single-mode and multi-mode fiber?

1. Core diameter

The main difference between multi-mode and single-mode fibers is that the former have larger diameters, typically 50 or 62.5 m core diameters, while typical single-mode fibers are 8 and 10 m core diameters, both with cladding diameters of 125 m.

single-mode         multi-mode 

2.light source

Lasers and leds are usually used as light sources. Laser light sources are significantly more expensive than LED light sources because the light they produce can be precisely controlled and has high power. The light produced by LED sources is more diffuse (many modes of light), and these sources are mostly used in multi-mode fiber jumpers. At the same time, laser light sources (which produce light close to a single mode) are usually used for single-mode fiber patch cord.

3. bandwidth because multi-mode fiber has a larger core size than single-mode fiber, it supports multiple transmission modes. In addition, like multi-mode fiber, single-mode fiber also exhibits modal dispersion caused by multiple spatial modes, but the modal dispersion of single-mode fiber is smaller than that of multi-mode fiber. For these reasons, single-mode fiber has a higher bandwidth than multi-mode fiber.

4. Jacket color The jacket color is sometimes used to distinguish multi-mode fiber jumpers from multi-mode fiber jumpers. According to tiA-598C standard definition, non-military use, single-mode optical fiber with yellow jacket, and multi-mode optical fiber with orange or aqua jacket. Depending on the type, some vendors use purple to distinguish high-performance OM4 fiber from other types of fiber.

5.mode dispersion

LED light sources are sometimes used in multi-mode fibers to create a range of wavelengths that propagate at different speeds. This leads to multi-mode dispersion, which limits the effective transmission distance of a multi-mode fiber jumper. In contrast, a laser used to drive a single-mode fiber produces a single wavelength of light. Therefore, its modal dispersion is much less than that of a multi-mode fiber Because of modal dispersion, multimode fiber has higher pulse propagation rate than single-mode fiber, which limits the information transmission capacity of multimode fiber.

6.Price

For multi-mode fiber, which can support multiple optical modes, it is more expensive than single-mode fiber. However, in terms of equipment, single-mode fiber equipment is more expensive than multi-mode fiber equipment, because single-mode fiber usually uses solid-state laser diodes. Therefore, the cost of using multi-mode fiber is much less than the cost of using single-mode fiber.