A. According to the transmission mode of light in optical fiber, it can be divided into single-mode fiber and multimode fiber.
Multimode optical fiber: The central glass core is thick (50 or 62.5μm), which can transmit multiple modes of light. However, its large intermodal dispersion limits the frequency of transmitting digital signals, and it will become more serious with the increase of distance. For example, a 600MB/KM optical 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: The glass core in the center is thin (the core diameter is generally 9 or 10μm) and can only transmit one mode of light. Therefore, its intermodal dispersion is very small, which is suitable for long-distance communication, but its dispersion plays a major role. Therefore, single-mode fiber requires high spectral width and stability of light source, that is, narrow spectral width and good stability.
B according to the optimal transmission frequency window, it can be divided into conventional single-mode fiber and dispersion-shifted single-mode fiber.
Conventional type: optical fiber manufacturers optimize the transmission frequency of optical fiber at a single wavelength, such as 1300nm.
Dispersion shift type: optical fiber manufacturers optimize the transmission frequency of optical fiber at two wavelengths, such as 1300nm and 1550nm.
C. According to the refractive index distribution, it can be divided into abrupt fiber and graded fiber.
Abrupt type: The refractive index from the central core of the optical fiber to the glass cladding is abrupt. It has low cost and high dispersion between modules. Suitable for short-distance low-speed communication, such as industrial control. However, due to the small dispersion between modes, single-mode fibers are all abrupt.
Graded fiber: the refractive index decreases gradually from the central core of the fiber to the glass cladding, which can make the high-mode light propagate in sinusoidal form, reduce the intermodal dispersion, increase the bandwidth of the fiber and increase the transmission distance, but the cost is higher. Nowadays, multimode fibers are mostly graded fibers.
4. Commonly used optical fiber specifications:
Single mode: 8/ 125μm, 9/ 125μm,10/125μ m.
Multimode: 50/ 125μm, European standard; 62.5/ 125μm, American standard
Industrial, medical and low-speed networks: 100/ 140μm, 200/230μ m.
Plastic: 98/ 1000μm, used for automobile control.