*Introductory Chapter: Fiber Optics DOI: http://dx.doi.org/10.5772/intechopen.85495*

*Fiber Optics - From Fundamentals to Industrial Applications*

Manfred Börner.

technology.

transmission time.

between Europe and the United States.

example, with variable structures of the glass fiber.

into the technical realization—until today. All optical long-distance transmission systems are also currently working according to this system principle proposed by

However, there was still a lot to improve. Because the data transfer did not really work well as the light intensity was simply too low, only short transmission distances were possible. One of the solutions to—at least this problem—was actually quite simple. The fiber material had minimal scratches, cracks, and bumps. Charles Kuen Kao has improved the fiber glass in 1966 and solved the problem. He received the Nobel Prize in 2009 for this and for further developments in fiber optic

And yet, even the best and clearest glass fibers have natural limits. Therefore, it is necessary to amplify the light signal after a certain distance. Initially, intermediate stations were set up, in which the incoming light signal was first converted into an electrical signal—and then again into a light signal. As a result, it had the initial light intensity again and could be transmitted over a long distance. However, this solution was unsatisfactory because the intermediate stations drastically increased

To solve this problem, purely optical amplifiers have been developed. With this, it was finally possible to guide the light without interruption over very long distances. The most important and widespread optical amplifier is the erbium-doped fiber amplifier [6]. In this case, a part of the cable is made of a special material that amplifies the light synchronously and seamlessly. The erbium-doped fiber amplifier works much like a laser where the active material (erbium), incorporated in the cable, is pumped to a population inversion state producing a regeneration of the signal intensity by stimulated emission [7]. The data transfer keeps hereby finally its fast pace without interruption of the propagation along the fiber cable. That is why it is on the longest transmission lines in the world, on the transatlantic route

In a further step, several carrier wavelengths are transmitted through a single fiber to increase the information capacity. For this purpose, the wavelengths are all first brought together, which is known as multiplexing. At the receiver side, the wavelengths are separated again by demultiplexing. The further development of fiber transmission is not yet finished. Researchers see further potential, for

A new generation of optical fiber has a fiber core, which is interspersed with holes. In this case, the light is confined not only in the core material but also in the holes or, in particular, in a larger hole in the middle of the fiber core. This works like a veritable turbo in the speed of data transmission. After all, light is extremely fast at around 300,000,000 km/s in vacuum. Unfortunately, the fiber material slows

A much better material, then, would simply be air, because it simply slows down less than glass or silicon. That is why researchers at the University of Southampton in 2013 developed a hollow core fiber in which the data could be transmitted at a rate of about 99.7% of the speed of light in vacuum [8]. Thus, data can be transmit-

Current research is also focusing on new modulation formats to increase the data rate and, therefore, to unleash the whole potential of optical communication. Such modulation formats employ different physical properties of light such as the amplitude, phase, and wavelength. During the last decades, several modulation formats like phase shift keying (PSK) and amplitude shift keying (ASK) but also advanced modulation formats such as m-th order quadrature amplitude modulation (QAM), binary phase shift keying (BPSK), and m-ASK were realized [9]. To generate such higher modulation formats, novel electrooptical modulators [10–12] are

down considerably, by around 30% due to the larger refractive index.

ted even faster or even more data can be transmitted at the same time.

**4**

combined with optical fibers, which is known as active optical fibers. These fibers are of special interest for rack-to-rack applications.

Optical fibers play a crucial role in telecommunication. Applications can be found in many areas such as optical fiber lasers [13], optical fiber interferometers [14, 15], optical fiber amplifier [16], and optical fiber sensors [17]. Especially the latter one has widespread applications in detecting magnetic fields [18], humidity [19], temperature [20], or biological molecules [21].
