Preface

Optical fibers in metrology, telecommunications, sensors, manufacturing, and health science have gained massive research interest. This book covers materials, components, and systems across the application spectrum, from interferometers for spectroscopy to fiber optic applications in medicine. Furthermore, the number of fields of application of optical fibers is increasing at a fast pace. On the other hand, the literature on optical fibers and the foundations of their functioning are extremely vast and we have no ambition to make an original contribution in this respect. This book aims to present a collection of recent advances in fiber optics. It covers the current progress and latest breakthroughs in emergent applications of fiber optics and specialty fibers.

The book includes five contributions on recent developments in optical fiber communications and fiber sensors, as well as the design, simulation, and fabrication of novel fiber concepts.

The editors Patrick Steglich and Fabio De Matteis provide a brief historical overview of important developments in the field of optical fibers, as well as current trends and perspectives.

Xiaoshuai Liu and Yao Zhang review the multifunctional manipulation for biological cells based on the elaborately designed fiber probes.

Monika Bahl describes the propagation of structured light fields in optical fibers, which find important applications in ICT but also in the design of ultrapowerful microscopes and novel spectroscopic analyses.

Yoshito Shuto presents a theoretical study on the evolution of a fiber fuse in a single-mode optical fiber. A novel nonlinear oscillation model using the Van der Pol equation is described and both the silica-glass densification and cavity formation observed in fiber fuse propagation are qualitatively explained.

Jing Wang, Zhensheng Jia, Luis Alberto Campos, and Curtis Knittle propose and demonstrate a delta-sigma digitization and coherent transmission of DOCSIS 3.1 signals for the first time.

We thank all authors for their contributions.

Finally, we express a great deal of thanks to the editing staff of IntechOpen, particularly Ms. Lada Bozic, for all their efforts.

> **Dr. Patrick Steglich** IHP—Leibniz-Institute for Innovative Microelectronics, Germany

> > Technical University of Applied Sciences Wildau, Germany

> > > **Dr. Fabio De Matteis** University of Rome "Tor Vergata", Italy

> > > > **1**

Section 1

Introduction

Section 1 Introduction

**3**

**Chapter 1**

**1. Introduction**

speed data communication.

Introductory Chapter: Fiber Optics

Whether covering a few meters or hundreds of kilometers, optical fibers allow to transmit information in a short time. Without communication over long distances, humankind would not have got far. It is the basis of every economic and political development. Up to the twentieth century, however, it was still the stagecoach that brought the information from A to B most quickly—at a speed of no more than 40 km an hour. Nowadays, optical fibers and light-wave technologies enable high-

In summary, this means that long-distance communication works in principle just like a Morse telegraph: a combination of pulsed signal travels in a medium bringing a coded information. The only difference is that we no longer send the signals with electricity, but with light. Indeed, optical fibers carry light in the visible and near-infrared region (∼100 THz), and therefore, they are often called lightwave systems to distinguish them from microwave systems (∼1 GHz) [1].

The principle is actually the same as in the Morse telegraph. Just as at the end of the 18th century, information is assigned to specific signals or light pulses. However, the copper cable was unsuitable for this purpose. In 1965, Manfred Börner, a German physicist, used a laser instead of a broadband light source to

A typical fiber optic cable, as used by Manfred Börner and currently used all over the world, consists usually of a fiberglass core covered by a fiberglass cladding. To protect against external influences and to prevent scratches or dirt and moisture from penetrating, the entire fiber is covered with a protective layer. The material of the cladding must have a smaller refractive index than the material of the core [2]. This allows for total internal reflection, a phenomenon well known since the first

It is noteworthy that for more than a century the total internal reflection was mostly used for illumination systems and image transmission to short distances. The first person to try to transmit images by means of a bundle of optical fibers was

In 1954, van Heel [4], on one side, and Hopkins and Kapany [5], on the other, simultaneously reported a way of conveying optical images along a glass fiber; in particular, the former writes: "*Preliminary experiments, started in January 1950, have shown that coating the fibres with silver or any other metal yields an unsatisfactory transmission. A much better result was obtained when the fibres were coated with a layer of lower refractive index, which ensured total reflexion*". The optical fiber was born. However, for a breakthrough in optical communications, it has been necessary to wait for Börner to first use a fiber-optic cable in combination with a laser. So here he had built a true optical data transmission system. He also employed photodetectors at the end of the fiber optic cable. In 1966, Börner applied for a patent for the system for the targeted transmission of information via optical fibers for the company AEG-Telefunken. And then, it finally came out of the experimental phase

transmit information with optical fibers for the first time.

half of the nineteenth century (Colladon and Babinet, Tyndall).

Heinrich Lamm, the first to propose a fiber-optic endoscope in 1930 [3].

*Patrick Steglich and Fabio De Matteis*
