What is single-mode fiber? What are the advantages and disadvantages?

Single-mode fiber (SingleModeFiber) is an optical fiber that can only transmit one mode at a specified wavelength. The center glass core is very thin (core diameter is generally 9 or 10μm).

Therefore, its inter-mode dispersion is very small, suitable for remote communication However, there are also material dispersion and waveguide dispersion, so that the single-mode fiber has higher requirements on the spectral width and stability of the light source, that is, the spectral width should be narrow and the stability is better.

Later, it was found that at 1.31μm wavelength, the material dispersion of the single-mode optical fiber and the waveguide dispersion are positive and negative, and the magnitude is exactly the same. In this way, the 1.31μm wavelength region has become an ideal working window for optical fiber communications, and is now the main working band of practical optical fiber communication systems. The main parameters of 1.31μm conventional single-mode fiber are recommended by the International Telecommunication Union ITU-T in G652 Certain, so this fiber is also called G652 fiber. Single-mode fiber can be divided into 652 single-mode fiber, 653 single-mode fiber and 655 single-mode fiber.

The explanation of “single-mode fiber” in academic literature: generally, when v is less than 2.405, only one peak in the fiber passes, so it is called a single-mode fiber. Its core is very thin, about 8-10 microns, and the mode dispersion is very Small. The main factor that affects the width of the fiber transmission band is various dispersions, and mode dispersion is the most important. The dispersion of single-mode fiber is small, so it can transmit light in a wide frequency band for a long distance.

The single-mode fiber has a core diameter of 10 micron, which allows single-mode beam transmission, which can reduce the bandwidth and Modal Dispersion. However, because the single-mode fiber core diameter is too small, it is difficult to control the beam transmission, so it is necessary to Expensive lasers are used as the light source, and the main limitation of single-mode optical cables is material dispersion. Single-mode optical cables mainly use lasers to obtain high-frequency bandwidth. Since LEDs will emit a large number of light sources with different bandwidths, material dispersion requirements are very important. Single-mode fiber can support longer transmission distance than multi-mode fiber. In 100Mbps Ethernet or 1G Gigabit network, single-mode fiber can support transmission distance of more than 5000m from a cost perspective. From the perspective of cost, since the optical transceiver is very expensive, the cost of using single-mode optical fiber will be higher than the cost of multi-mode optical fiber cable.

The refractive index distribution is similar to the abrupt optical fiber, the core diameter is only 8 ~ 10μm, and the light propagates in a linear shape along the core axis. Because this fiber can only transmit one mode (the two polarization states are degenerate), it is called a single-mode fiber and its signal distortion is very small.