Special Optical Communications: Types of Fiber

Our special on optical communications we have reviewed the history of optical communications to reach optical fiber, then give way to the principles on which this technology and some of its applications are based. At this point it only remains to know the different types of optical fiber and how light propagates through them.

Fibers Index Jump

Index jump

As the name suggests, it consists of a thread made of a material (core) with a certain refractive index (density) covered with another material (coating) with a lower refractive index. This produces a joint that facilitates the total internal reflection and therefore the beam of light stays within the fiber.

The problem of this type of fibers is that they are very complicated to manufacture since any type of imperfection in the joint, such as an air bubble, means that there is no longer such a border, reflection does not occur and therefore the beam does not arrive of light at the other end. In addition, they have a problem of modal dispersion.

Modal dispersion is the time difference between the first beams of a pulse until the last beam of that same pulse arrives. To know more Cable companies .This occurs because not all rays travel the same distance. In the figure above we can see how the beam drawn with a more intense red bounces more times than the rest, so it travels longer and takes longer to reach than the beam that has bounced less.

One way to avoid the modal dispersion, or at least reduce it, is to make the fibers as thin as possible, however, this increases the attenuation or introduce as few rays into the fiber as possible.

Index Gradient Fibers

Index gradient

In this type of fibers the border does not exist as such, instead of causing a sudden change in the refractive index, what is sought is a gradual change. This modification causes the beam of light to curve gradually instead of "bouncing". In addition, it produces an effect that did not occur in the index jumping fibers, the periodic passage through the center of the fiber.

This system is easier to manufacture since during the yarn manufacturing process it is "played" with the cooling speed of the material so that the refractive index is higher in the core and decreases as we move away from it. In contrast, these types of fibers are not as fast as the index jump. On the other hand, this process achieves that the light beams that travel through the center of the fiber spread more slowly than those that travel along the edges (those that have to give more curves), thanks to this it is achieved that all the beams they arrive more together, although slower, facilitating communication