OPTICAL FIBER

The light produced by diodes or by lasers travels through the core due to the reflection that occurs in the cover, and is converted into an electrical signal at the receiving end.
Optical fiber is an excellent medium for the transmission of information due to its excellent characteristics: high bandwidth, low signal attenuation, integrity, immunity to electromagnetic interference, high security and long life. Its greatest disadvantage is its higher production cost than other types of cable, due to the need to use high-quality glass and the fragility of its handling in production. The termination of fiber optic cables requires a special treatment that causes an increase in installation costs.
One of the most characteristic parameters of the fibers is their relationship between the refractive indices of the core and the cover, which also depends on the radius of the core and is called the fundamental or normalized frequency; it is also known as numerical aperture and is dimensionless. According to the value of this parameter, fiber optic cables can be classified into two classes:

• singlemode. When the value of the numerical aperture is less than 2,405, a single electromagnetic mode travels through the line and therefore it is called single mode. Only rays parallel to the axis of the optical fiber are propagated, achieving maximum performance, specifically a bandwidth of up to 50 GHz.
  This type of fiber requires the use of laser emitters for the injection of light, which provides a large bandwidth and low attenuation over distance, which is why they are used in metropolitan networks and wide area networks. On the other hand, they are more expensive to produce and the equipment is more sophisticated. It can operate with speeds of up to 622 Mbps and has a transmission range of up to 100 km.
• multimode When the value of the numerical aperture is greater than 2,405, several electromagnetic modes are transmitted through the fiber, for this reason it is called multimode fiber.
  Multimode fibers are the most used in local networks due to their low cost. The most frequent diameters are 62,5/125 and 100/140 microns. The transmission distances of this type of fiber are around 2,4 km and are used at different speeds: 10 Mbps, 16 Mbps, 100 Mbps and 155 Mbps.

  TYPES OF MULTIMODE

  • With index jump. The optical fiber is composed of two structures that have different refractive indices. The wavelength signal not visible to the human eye propagates by reflection. This achieves a bandwidth of up to 100 MHz.
  • With gradual index. The refractive index increases proportionally to the radial distance from the axis of the optical fiber. It is the most widely used fiber and provides a bandwidth of up to 1 GHz

The general characteristics of fiber optics are:

Bandwidth: Fiber optics provide significantly higher bandwidth than paired cables (UTP/STP) and Coaxial. Although speeds of 1,7 Gbps are currently being used in public networks, the use of higher frequencies (visible light) will allow reaching 39 Gbps. The bandwidth of the optical fiber allows the transmission of data, voice, video, etc.
Distance: The low attenuation of the optical signal allows fiber optic cables to be laid without the need for repeaters.
data integrity: Under normal conditions, a fiber optic data transmission has an error frequency or BER (Bit Error Rate) less than 10 E-11. This feature allows high-level communication protocols not to need to implement error correction procedures, thus speeding up the transfer speed.
Duration: The optical fiber is resistant to corrosion and high temperatures. Thanks to the protection of the casing, it is capable of withstanding high tension stresses in the installation.
Safety: Because fiber optics do not produce electromagnetic radiation, they are resistant to intrusive eavesdropping. To access the signal that circulates in the fiber it is necessary to split it, with which there is no transmission during this process, and it can therefore be detected.
The fiber is also immune to external electromagnetic effects, so it can be used in industrial environments without the need for special protection.