Optical fiber category (1)

Optical fiber category (1)

There are many types of optical fibers and various classification methods.

From the material point of view

According to the materials used for optical fiber manufacturing, there are Z optical fiber, multi-component glass optical fiber, plastic package layer Z core optical fiber, all plastic optical fiber and fluoride optical fiber.

Plastic Optical Fiber is made of highly transparent polystyrene or polymethyl methacrylate (plexiglass. It features low manufacturing costs, relatively large core diameter, high coupling efficiency with the light source, large optical power coupling into the optical fiber, easy to use. However, due to high loss and low bandwidth, this optical fiber can only be used for short-distance and low-speed communication, such as short-distance computer network links and intra-ship communication. Currently, Z optical fiber is widely used in communication.

By transmission mode

The transmission modes of optical fiber include single-mode optical fiber and multi-mode optical fiber.

The fiber core diameter of multimode optical fiber is 50 ~ 62.5 μm, the outer diameter of the package layer is 125 μM, the core diameter of the single-mode optical fiber is 8.3 μm, and the outer diameter of the package layer is 125 μM. The optical fiber working wavelength is short wavelength of 0.85 μm, long wavelength of 1.31 μm and 1.55 μm. The optical fiber loss usually decreases with the wavelength length. The loss of 0.85 μm is 2.5dB/km, the loss of 1.31 μm is 0.35dB/km, and the loss of 1.55 μm is 0.20dB/km, this is the lowest loss of optical fiber, and the loss of a wavelength of more than 1.65 μm tends to increase. Because of the absorption function of OH queue, 0.90 ~ 1.30 μm and 1.34 ~ There is a loss peak in the 1.52 μm range, and these two ranges are not fully utilized. Since 1980s, it is preferred to use single-mode optical fiber and use a long wavelength of 1.31 μm.

Multimode Optical Fiber

Multi-Mode Fiber: the center glass core is coarse (50 or 62.5 μm) and can transmit light in multiple modes. However, the color difference between them is large, which limits the frequency of digital signal transmission and increases with the increase of distance. For example, 600 MB/KM optical fiber only has 2KM MB of bandwidth. Therefore, multimode optical fiber transmission distance is relatively close, generally only a few kilometers.

Single-Mode Optical Fiber

Single Mode Fiber: the center glass core is very small (the core diameter is usually 9 or 10 μm), and only one Mode of light can be transmitted. Therefore, the mode color dispersion is small, which is suitable for remote communication, but there are still material dispersion and Waveguide Dispersion. In this way, the single-mode optical fiber has a high requirement on the spectral width and Stability of the light source, that is, the spectral width must be narrow, good stability. Later, it was found that at the wavelength of 1.31 μm, the material dispersion of the single-mode optical fiber and the Waveguide Dispersion were positive and negative, and the size was exactly the same. This means that at the wavelength of 1.31 μm, the total dispersion of a single-mode optical fiber is zero. According to the optical fiber loss characteristics, the 1.31 μm position is exactly a low-loss window of the optical fiber. In this way, the 1.31 μm wavelength zone becomes an ideal working window for optical fiber communication, and is also the main working band of the current practical optical fiber communication system. The main parameters of 1.31 μm conventional single-mode optical fiber are determined by the ITU ITU-T in G652 recommendations, so this kind of optical fiber is also called G652 optical fiber.

Best transmission window

According to the Optimal Transmission frequency window: conventional single-mode optical fiber and dispersion displacement single-mode optical fiber.

Conventional: Optical Fiber Production experts optimize the optical fiber transmission frequency on a single wavelength of light, such as 1300 μm.

Dispersion Displacement Type: Optical Fiber manufacturers optimize the optical fiber transmission frequency on two wavelengths of light, such as 1300 μm and 1550 μm.

We know that a single-mode optical fiber has a high bandwidth because it has no mode dispersion. If a single-mode optical fiber is working in a wavelength of 1.55 μm, can it achieve high bandwidth and low-loss transmission? But it is not that simple. The dispersion of a conventional single-mode optical fiber at 1.31 μm is much smaller than that at 1.55 μm. Such optical fiber works in a wavelength of 1.55 μm. Although the loss is low, the dispersion will seriously affect the high-speed optical communication system. Therefore, this optical fiber is still not an ideal transmission medium.

In order to make the optical fiber work well at 1.55 μm, we have designed a new optical fiber called the dispersion displacement optical fiber (DSF ). This optical fiber can compensate for the dispersion, so that the zero-color scatter of the optical fiber is moved from 1.31 μm to 1.55 μm. This type of optical fiber is also known as a 1.55 μm zero-dispersion single-mode optical fiber, codenamed G653.

G653 optical fiber is an excellent transmission medium for single-channel and ultra-high-speed transmission. Currently, this type of optical fiber has been used for communication trunk networks, especially for optical fiber communication systems with high speed and long relay distance.

Although the dispersion displacement optical fiber is ideal for single-channel and ultra-high-speed transmission, when it is used for Wavelength Division Multiplexing multi-channel transmission, it will also interfere with the transmitted signal due to the non-linear effect of the optical fiber. Especially near the wavelength with zero dispersion, interference is particularly serious. To this end, a non-zero dispersion displacement Optical Fiber G655 optical fiber was developed, which moved the zero color scatter of the optical fiber to 1.55 μm outside the work zone or before 1.60 μm, however, the dispersion remains low in the 1.55 μm wavelength zone. This non-zero dispersion displacement optical fiber can be used not only for single-channel and ultra-high-speed transmission, but also for future expansion using wavelength division multiplexing, it also takes into account the ideal transmission media for future development.

There is also a single-mode optical fiber that is a dispersion flat type single-mode optical fiber. The dispersion of the optical fiber from 1.31 μm to 1.55 μm is very flat and close to zero. However, the loss of such optical fiber is difficult to reduce, which does not reflect the advantages brought about by the reduction of dispersion. Therefore, it has not yet entered the practical stage.