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The differences and choice of intelligentize weak current engineering single mode and multimode fiber cable


What are the single mode fiber cable and multimode fiber cable? And what are the distinctions between them? The conceptions of single mode and multimode classify the optic fiber according to propagation modes--the multimode fiber and single mode fiber propagation mode concepts. As we all know, light is a kind of electromagnetic wave with an extremely high frequency (3×1014HZ). When it transmits in the fiber optic light cable, according to the theory of wave optics, electromagnetic field, and solving Maxwell's equations, we find that:

When the geometric size of the optical fiber core is much larger than the optical wavelength, the light will propagate in the optical fiber in dozens or even hundreds of modes, such as TMmn mode, Temn mode, HEmn mode, etc. (where m, n=0, 1, 2, 3...).

The module HE11 is called the fundamental module, and the others are called higher-order modules.

Multimode fiber

When the geometric size of the optical fiber (mainly is the diameter of the fiber core d1) is by far more than the wavelength (about 0.1µm), there are dozens of or even hundreds of propagation modes in the optical fiber. Different propagation modes possess distinctive transmission speed and phases, which causes the generation of the delay and widening fiber pulse after the long-distance transmission. The phenomenon is called mode dispersion of optical fibers (also called mode dispersion).

The mode dispersion will make the bandwidth of multimode fiber narrow down and decrease its transmission volume. Therefore, the multimode fiber is only applied to the optical fiber communication with a small volume.

Most of the refractive index distribution of multimode fibers is a parabola, a gradient refractive index distribution, and its fiber core diameter is about 50µm.

Single-mode fiber

When the geometrical size (mainly core diameter) of the fiber is close to the wavelength of the light, such as core diameter D1 in the range of 5 ~ 10µm, only one mode (fundamental mode HE11) is allowed to propagate in the fiber, and the rest of the higher-order modes are all cut off. And such fiber is called single-mode fiber.

Because it only possesses one propagation mode and avoids the problem of mode dispersion, the single-mode fiber has ultra-expanded bandwidth, and it is especially suitable for fiber communication with a large capacity. Therefore, if you want to realize the single-mode transmission, you have to make all the parameters of optical fiber content with a certain condition. According to the calculation formula, for the fiber with Na =0.12 to achieve single-mode transmission above λ=1.3 m, the radius of the fiber core should be less than 4.2 m, that is, the diameter of the fiber core D1 ≤8.4 m.

The fiber core diameter of single mode fiber optic cable is pretty thin, so the requirement of its manufacturing process is more strict.

In summary, we mainly choose the fiber cable types according to the volume of the optical fiber communication and the parameters of optical fiber. And hope this passage will help you distinguish between the multimode fiber cable and single mode fiber cable. COMAX, focusing on fiber cable manufacturing, has over 6 years of experience. If you would like to know more about fiber cables, welcome to visit our website: www.comaxfibercable.com and contact us.