How to distinguish SM and MM fiber？
May 07 , 2021
According to the transmission mode of light in the fiber, it can be divided into: single-mode fiber and multi-mode fiber.
The core diameter of the multimode fiber is 50-62.5μm, the outer diameter of the cladding is 125μm, the core diameter of the single-mode fiber is 8.3μm, and the outer diameter of the cladding is 125μm. The working wavelength of the optical fiber has short wavelength 0.85μm, long wavelength 1.31μm and 1.55μm. Fiber loss generally decreases with the lengthening of the wavelength. The loss of 0.85μm is 2.5dB/km, the loss of 1.31μm is 0.35dB/km, and the loss of 1.55μm is 0.20dB/km. This is the lowest loss of the fiber, with a wavelength of 1.65 The loss above μm tends to increase. Due to the absorption of OHˉ, there are loss peaks in the ranges of 0.90~1.30μm and 1.34~1.52μm, and these two ranges are not fully utilized. Since the 1980s, single-mode fibers have tended to be used more often, and the long wavelength 1.31μm has been used first.
Multimode fiber
Fiber): The central glass core is relatively thick (50 or 62.5μm), which can transmit multiple modes of light. However, the inter-mode dispersion is relatively large, which limits the frequency of the transmission of digital signals, and it becomes more serious with the increase of distance. For example: 600MB/KM fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber is relatively short, generally only a few kilometers.
Single mode fiber
Fiber): The central glass core is very thin (the core diameter is generally 9 or 10 μm) and can only transmit one mode of light. Therefore, the inter-mode dispersion is very small, which is suitable for long-distance communication, but there are material dispersion and waveguide dispersion. In this way, single-mode fibers have higher requirements on the spectral width and stability of the light source, that is, the spectral width should be narrow and stable. Better. Later, it was discovered that at the wavelength of 1.31μm, the material dispersion and waveguide dispersion of the single-mode fiber were positive and negative, and the magnitudes were exactly the same. This means that at a wavelength of 1.31μm, the total dispersion of a single-mode fiber is zero. From the point of view of the loss characteristics of the optical fiber, 1.31μm is just a low loss window of the optical fiber. In this way, the 1.31μm wavelength region has become a very ideal working window for optical fiber communication, and it is also the main working band of the current practical optical fiber communication system. The main parameters of 1.31μm conventional single-mode fiber are determined by the International Telecommunication Union ITU-T in the G652 recommendation, so this fiber is also called G652 fiber
2. Are single-mode and multi-mode technologies produced at the same time? Is it more advanced
Multi-mode first
I can’t talk about the more advanced ones. Generally, the short distance ones use multi-mode, and the far ones use single-mode ones, because the transceivers of multi-mode fiber are much cheaper than single-mode ones.
3. Single-mode fiber is used for long-distance transmission, and multi-mode fiber is used for indoor data transmission.
Long-distance can only use single mode, but indoor data transmission does not necessarily use multi-mode
4. Is the fiber used in servers and storage devices single-mode or multi-mode?
Most of them use multi-mode, because I just do communication optical fiber is not too clear about this problem.
5. Does the optical fiber have to be used one-to-one? Is there any equipment such as single-hole single-mode fiber signal converter?
Does the optical fiber have to be used one-to-one? Yes, the latter half of the question do you mean to receive and emit light on a single optical fiber? This is possible, China Telecom's 1600G backbone optical fiber network is like this.
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