Single mode fiber: the central glass core is very thin (core diameter is generally 9 or 10 μ m) , there is only one transmission mode of optical fiber. The transmission loss and dispersion of single-mode fiber are relatively small. Small transmission loss can make the distance of signal transmission in optical fiber longer. Small transmission dispersion is conducive to high-speed and high-capacity data transmission. Therefore, in communication systems, especially high-capacity communication systems, single-mode optical fibers are mostly used.

According to ITU-T recommendations of the International Telecommunication Union, single-mode optical fibers can be divided into six types: G.652 (dispersion non displacement single-mode optical fiber), G.653 (dispersion displacement optical fiber), G.654 (cut-off wavelength displacement optical fiber), G.655 (non-zero dispersion displacement optical fiber), G.656 (low slope non-zero dispersion displacement optical fiber) and G.657 (bending resistant optical fiber) single-mode optical fibers, of which G.652 and G.655 single-mode optical fibers are the most common types.

Compared with multimode fiber, single-mode fiber can support longer transmission distance. In 100Mbps Ethernet and 1G gigabit network, single-mode fiber can support transmission distance of more than 5000m.

Explanation of "single-mode fiber" in academic literature: generally, when v is less than 2.405, only one wave peak passes through the fiber, so it is called single-mode fiber. Its core is very thin, about 8-10 microns, and its mode dispersion is very small. The main factors affecting the width of optical fiber transmission band are various dispersion, and the modal dispersion is the most important. Single mode fiber has small dispersion, so it can transmit light over a long distance with a very wide frequency band.

Single mode optical fiber has a core diameter of 10micron, which allows transmission of single mode light beam, and can reduce the limits of bandwidth and modal dispersion. However, because the core diameter of single mode optical fiber is too small, it is difficult to control the beam transmission, so extremely expensive laser is required as the light source. The main limitation of single mode optical fiber cable is material dispersion. Single mode optical fiber cable mainly uses laser to obtain high bandwidth, Since LED will emit a large number of light sources with different bandwidth, the material dispersion requirements are very important.

From the cost point of view, because the optical transceiver is very expensive, the cost of using single-mode fiber will be higher than that of multimode fiber cable.

Single Mode Fiber (SMF)

Compared with multimode fiber, the core diameter of single-mode fiber is much smaller, only 8-10 μ m。 Because only one mode is transmitted, there is no inter mode dispersion, the total dispersion is small, and the bandwidth is wide. Single mode optical fiber is used in 1.3~1.6 μ In the wavelength region of m, through the proper design of the refractive index distribution of the fiber and the selection of materials with high purity to prepare the cladding which is 7 times larger than the fiber core, lower loss and smaller dispersion can be achieved simultaneously in this band.

Single mode optical fiber is used in long-distance and high-capacity optical fiber communication systems, optical fiber local area networks and various optical fiber sensors.