**2. Optical fiber transmission**

From the invention of optical fibers to the present day, research and technological development on optical fibers has been carried out [6]. The use of semiconductor devices coupled to fiber-optics in technological development for the transmission of information has evolved over time since 1980. Five generations of technological development have been implemented where fiber-optic technology coupled to semiconductor materials has increased the amount of information as well as the distance between repeaters (**Table 1**).


#### **Table 1.**

*Evolution of different generations of light wave systems.*

#### **Figure 4.**

*Increase in the BL product from 1975 to 2000 through four generations of light wave systems. Different symbols are used for successive generations [4].*

**Figure 4** shows the evolution of the first four generations of optical fiber coupled with laser devices as an emission source. Two mechanisms can be mentioned about the fourth generation to amplify the information that reaches a system; these are the rare earth-doped amplifiers and semiconductor amplifiers [7, 8]. Additionally as mentioned in the fifth generation, there are Raman amplifiers [9].

Among the amplifiers doped with rare earths, those made with fiber-optic doped with erbium and doped with ytterbium can be mentioned [10–12]. The optical fibers doped with erbium are the most used for the construction of this type of amplifiers, among other sensors and other applications [13–16]. The above due to its low cost compared to the ytterbium and because its amplification window coincides with the third transmission window of silica-based optical fibers [17].
