**1. Optical fibers**

The optical fibers invented by Kapany [1], based on the observations that John Tyndall made a few years before, have become the object of research, technological development, and applications to this day.

The optical fibers have the ability to transport a large amount of information between two points (emitter-receiver). Unlike the conductive cables that are commonly used for sending information, fiber-optic cables offer the advantage of being very light [2]. As for its physical characteristics, an optical fiber is commonly compared to a human hair whose diameter is around 120 μm [3]. In terms of capacity for sending information, they can carry up to 20 billion light pulses per second [3]. Nowadays, due to the high transmission capacity and low absorption losses in an optical fiber, it is possible to send information over distances of more than 100 km without the need for repeaters. To carry out the sending of information from one point to another by means of a fiber-optic system, three basic elements should be considered as mentioned in **Figure 1**:


In order to have mechanical support and total reflection of the light traveling in the fiber [4], avoiding absorption, the optical fiber is composed of three main elements (**Figure 2**):


#### **Figure 1.**

*Basic schema of an optical communication system.*

**Figure 2.** *Principal elements of an optical fiber.*

Due to their ease of manufacturing, the optical fibers are made of glass and plastic; however due to their performance, the optical glass fibers are the most used due to the transmission length and their efficiencies. Basically there are two types of optical fibers, and they are defined by their ability to transmit information, which implies the type of application [4]. Those fiber types are mentioned next:


**Figure 3** shows a graphic comparison of the expected behavior in the two types of the mentioned fibers; the way of sending information between the fibers can be noted.

When the copper transmission capacity comparison is made, which allows a few million pulses per second, versus more than 20 million pulses that can be sent in an optical fiber, it is possible to appreciate the great efficiency advantage. It is understandable that communications companies can work with large amounts of information that would be limited with the use of conductive cables. Therefore, the great increase in the transmission of information that we can see on the Internet and the Word Wide Web has been achieved [5].

**Figure 3.**

*Simple graphical comparison between single-mode and multimode optical fibers.*
