Optical fiber is the abbreviation of optical waveguide fiber. In fiber optical communication, fiber optical is usually simplified to Fiber. At present, there are many types of optical communications products, but there are roughly four types of classification methods, namely, classified according to the refractive index distribution of profile of fiber optical, classified according to the propagation mode, classified according to the working wavelength, and classified according to the type of plastic coating, etc.
① Step-index Fiber
Step-index Fiber means that in the fiber core and cladding regions, the refractive index distribution is uniform, and its values are n1 and n2, but at the boundary between the fiber core and the cladding, the change in refractive index is a step. Now, when single-mode fiber optical gradually replaces multi-mode fiber optical and becomes the mainstream product of current fiber optical, the step-index fiber structure is once again one of the structural forms of single-mode optical fiber.
② Graded-index fiber
The so-called graded-index fiber means that the maximum refractive index is at the axis of the fiber optical, which decreases with the increase in the radial direction of the section. The change rule generally conforms to the parabolic law. When the boundary between the fiber core and the cladding is reached, it just drops to the same value as the refractive index of the region; the distribution of the refractive index in the cladding region is uniform.
① Multi-mode optical fiber
Multi-mode fiber optical: The central glass core is 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, which will become more serious with the increase of distance.
② Single-mode optical fiber
Single-mode fiber: the central glass core is very thin (the core diameter is generally 9 or 10μm), because it only allows one mode to propagate in it, thus avoiding the problem of mode dispersion. Therefore, the single-mode fiber optical has an extremely wide bandwidth, which is especially suitable for large-capacity fiber optical communication.
① Short-wavelength fiber
In the early days of the development of fiber optical communications, the wavelength of light waves used by people was in the range of 0.6 to 0.9 microns (typical value is 0.85 microns). It is customary to call fiber optical products that exhibit low attenuation in this wavelength range as short-wavelength fiber optical. Short-wavelength fiber optical is an early product and is rarely used at present.
② Long-wavelength fiber
With the continuous deepening of research work, it was found that the attenuation of the quartz fiber optical dropped sharply near the wavelengths of 1.31 microns and 1.55 microns. Not only that, but also the material dispersion of the silica fiber optical in this wavelength range is greatly reduced. Therefore, people’s research work has shifted rapidly, and an fiber optical product in this range has been developed, which is called long-wavelength fiber optical. Long-wavelength fiber optical is especially suitable for long-distance, large-capacity fiber optical communication because of its low attenuation and wide bandwidth.
① Tight-buffered fiber
The so-called tight-buffered optical fiber refers to the fiber in which the secondary and tertiary coating layer and the pre-coating layer and the core and cladding of the fiber are tightly combined. At present, this type of fiber optical is used most.
The attenuation-temperature characteristics of uncoated fiber optical are very good, but its temperature characteristics decrease after coating. This is because the expansion coefficient of the coating material is much higher than that of quartz, and it shrinks more severely at low temperatures, compressing the fiber optical to bend slightly, and increasing the attenuation of the fiber.
② Loose-buffered fiber
The so-called loose-buffered optical fiber means that the pre-coated fiber is loosely placed in a plastic tube, and no secondary or tertiary coating is carried out.
The manufacturing process of loose-buffered fiber optical is simple, and its attenuation-temperature characteristics and mechanical properties are better than those of tight-buffered fiber, so more and more people pay attention to it.