1. Multi-mode optical fiber: When the geometric size of the optical fiber is much larger than the wavelength of the light wave, there will be dozens or even hundreds of propagation modes in the optical fiber.
Different propagation modes have different propagation speeds and phases, resulting in time delays and light pulse broadening after long-distance transmission.
This phenomenon is called modal dispersion of optical fiber.
Modal dispersion will narrow the bandwidth of multi-mode optical fiber and reduce its transmission capacity. Therefore, multi-mode optical fiber is only suitable for small-capacity optical fiber communications.
2. Single-mode optical fiber: When the geometric size of the optical fiber can be similar to the wavelength of light, the optical fiber only allows one mode to propagate in it, and all other higher-order modes are cut off. Such an optical fiber is called a single-mode optical fiber. .
Since it only propagates in one mode and avoids the problem of modal dispersion, single-mode optical fiber has an extremely wide bandwidth and is especially suitable for large-capacity optical fiber communications.
3. What are the advantages of using optical fiber? 1) The passband of optical fiber is very wide, theoretically up to 30T.
2) The support length without relay can reach tens to hundreds of kilometers, and the copper wire is only a few hundred meters.
3) Not affected by electromagnetic fields and electromagnetic radiation.
4) Light weight and small size.
5) Optical fiber communication is not electrified and is safe to use and can be used in flammable, explosive and other places.
6) The operating environment temperature range is wide.
7) Long service life.
4. How to choose optical cable? In addition to the number of fiber cores and fiber types, the selection of optical cables must also select the structure and outer sheath of the optical cable according to the environment in which the optical cable is used.
1. When directly burying optical cables for outdoor use, it is advisable to use loose-tube armored optical cables.
When used overhead, a loose tube optical cable with a black PE outer sheath with two or more reinforcing ribs can be used.
2. When selecting optical cables for use in buildings, tight-buffered optical cables should be selected and attention should be paid to their flame retardant, toxic and smoke characteristics.
Generally, flame-retardant but smokey type (Plenum) or flammable and non-toxic type (LSZH) can be used in pipes or forced ventilation areas. Flame-retardant, non-toxic and non-toxic types should be used in exposed environments. Type of smoke (Riser).
3. When laying vertical or horizontal cables in the building, you can use tight-buffered optical cables, distribution optical cables or branch optical cables that are common in the building.
4. Select single-mode and multi-mode optical cables according to network application and optical cable application parameters. Usually, indoor and short-distance applications are mainly multi-mode optical cables, and outdoor and long-distance applications are mainly single-mode optical cables.
