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Type of fiber

2018-12-11 193

a. According to the transmission mode of light in the optical fiber, it can be divided into single mode fiber and multimode fiber.

Multimode fiber: The center glass core is thicker (50 or 62.5 μm) and can transmit multiple modes of light. However, the dispersion between the modes is large, which limits the frequency of transmitting digital signals, and is more serious as the distance increases. For example, a fiber of 600 mb/km has a bandwidth of only 300 mb at 2 km. Therefore, the distance traveled by multimode fiber is relatively close, usually only a few kilometers. Single mode fiber: The center glass core is thinner (the core diameter is generally 9 or 10 μm) and can only transmit one mode of light. Therefore, the inter-mode dispersion is small, suitable for remote communication, but its chromatic dispersion plays a major role, so that single-mode fiber has high requirements on the spectral width and stability of the light source, that is, the spectral width is narrow and the stability is good. 

Single-mode fiber: Generally, the fiber jumper is indicated by yellow, the connector and the cover are blue, and the transmission distance is long. Multi-mode fiber: Generally, the fiber jumper is shown in orange, and some is shown in gray. The connector and cover are in beige or black; the transmission distance is short.

b. According to the optimal transmission frequency window: conventional single mode fiber and dispersion shifted single mode fiber.

Conventional: Fiber manufacturers optimize fiber transmission frequencies on a single wavelength of light, such as 1300 nm.

Dispersion-displacement type: The fiber production family optimizes the fiber transmission frequency to two wavelengths of light, such as 1300 nm and 1550 nm.

c. According to the refractive index distribution: mutant and graded fiber.

Mutant: The refractive index of the fiber core to the glass cladding is abrupt. The cost is low and the dispersion between the modes is high. Suitable for short-distance low-speed communication, such as: industrial control. However, single-mode fibers use a mutant type because of the small dispersion between modes.

Gradient fiber: The refractive index of the fiber core to the glass cladding is gradually reduced, which can make the high mode light propagate in a sinusoidal form. This can reduce the dispersion between modes, increase the fiber bandwidth, increase the transmission distance, but the cost is higher. Most of the mode fibers are graded fibers.