Preface

Optical fibers are of great interest for scientific and technological applications, especially in communications systems.

In the first section on technology, Chapter 1 discusses the technology that has been developed to generate better optical fiber products with increased transmission speed, such as multi-core fibers. Increased transmission rates can be achieved via the use of space division multiplexing, allowing for an increase in the information in one optical fiber. Of course, a multi-core fiber must be coupled with specific electronic and optoelectronic devices to increase its performance.

A wide variety of fiber devices can be created by adding special coatings on tapered sections of optical fibers. Chapter 2 presents the fundamentals for the fabrication of tapered optical fibers coated with functional polymers. Here, the required aspects of light propagation in tapered sections of optical fibers are introduced and the relevant parameters enabling light interaction with external media are discussed. A special case of interest is the addition of polymeric coatings with prescribed thicknesses in the tapered sections allowing for adjusting the light propagation features; using liquid polymer coatings with varying thicknesses along with the taper profile that can be tailored for tuning the transmission features of the devices. The chapter also presents a methodology for obtaining coatings with predefined geometries whose optical properties will depend on the polymer functionality.

Optical fiber networks are the standard applied for high-bandwidth customers. Various access technologies to business networks with very high bandwidth to access networks for buildings and individual consumers have emerged. Chapter 3 discusses the optical network connections inside buildings for commercial and domestic users, including the use of optical glass fibers or/and polymeric optical fibers in different network topologies in connection to high-speed actual WIFI technologies.

The second part of this book is dedicated to the application of optical fibers in communications. Chapter 4 deals with coded modulation and impairment compensation techniques in optical fiber communication. Probabilistic shaping is a new coded modulation technology that can reduce transmission power by precoding, reducing the bit error rate, and improving communication rate. In this chapter, a probabilistic shaping 16QAM modulation scheme based on trellis-coded modulation is proposed. Experimental results show that this scheme can achieve better optical SNR gain and BER performance. On the other hand, to meet the demand of transmission rate of next-generation high-speed optical communication systems, multidimensional modulation and coherent detection are sufficiently applied.

Nowadays, due to the renewed demand on data bandwidth imposed by the upcoming capacity crunch, the optical communication (research and industry) community has oriented its effort to space division multiplexing (SDM), particularly mode division multiplexing (MDM). This is based on separate/independent and orthogonal spatial modes of optical fiber as data carriers along with the optical fiber. Chapter 5 reviews the potentials of harnessing SDM as a promising solution for next-generation global communications. The study is focused on different SDM approaches and specifically addresses MDM (different modes in optical fiber).

developments. In that sense, this book covers a good diversity of topics from fiber optics technology development to communications systems and some applications

**Guillermo Huerta Cuellar**

Universitary Center of Lagos, University of Guadalajara, Lagos de Moreno, Mexico

Department of Exact Sciences and Technology,

for scientific research and technological devices.

Because of their versatility in different areas of science and technology, optical fibers have many important applications, as outlined in the last part of the book. Chapter 6 discusses the use of optical fiber tweezers for the assembly of living photonic probes, which are versatile tools for optical trapping and manipulation that have attracted much attention in cell trapping, manipulation, and detection. The assembly of living cells using optical fiber tweezers has attracted significant attention. Advanced achievements have been made on the assembly of fully biocompatible photonic probes with biological cells, enabling optical detection in a biological environment in a highly compatible manner. Living photonic probes can be assembled by trapping and assembling multiple cells using optical fiber tweezers. These photonic probes exhibit high biocompatibility and show great promise for bio-applications in bio-microenvironments.

Optical fiber sensing research has been extended to the area of detection of microorganisms such as bacteria, viruses, fungi, and protozoa. The validation of optical fibers in bio-sensing applications can be observed from the growing number of publications. Chapter 7 provides a brief picture of optical fiber biosensors, their geometries, and the procedures for their development.

Integration of optical fibers with optoelectronic devices is a very important application. In terms of communication systems, they are integrated with one or two technologies, as is the case for automation, image processing, and embedded systems. Chapter 8 is dedicated to recent results of artificial intelligence (AI) and photonics integration. Nowadays, photonics are used with AI to facilitate ultra-fast AI networks to offer a novel class of Information Processing Machines (IPMs). The chapter demonstrates the implementation of photonics for AI utility and AI for photonics. In this category, a dual-core photonic crystal fiber (PCF) integrated with AI is proposed, which serves to identify infected human cells. This proposed design of PCF is providing relative sensitivity and confinement loss in an optimized manner with the impact of AI.

The numerical approach for characterizing some applications is a very important tool. The final chapter of this book considers differential equations and analyzes methods with Opto-Electronic Oscillator (OEO) modulation with direct and external modulation. The complexity of both approaches is related to the non-standard way of description of the nonlinear method modulation for the internal (direct) structure and the utilization of the specific Mach-Zehnder modulator for the first stage of external modulation. The purpose of the presentation is to consider the main features of OEO as a low-noise generator. This includes consideration based on the study of differential equations, the study of transients in OEO, and the calculation of phase noise. It is shown that different types of fibers with low losses at small bending radii can be used as a FOLD in OEO.

This book was made possible thanks to the effort and dedication of researchers worldwide that want to share their knowledge with the world, facilitating the spread of different possible innovative experiments and technological

developments. In that sense, this book covers a good diversity of topics from fiber optics technology development to communications systems and some applications for scientific research and technological devices.

**Guillermo Huerta Cuellar**

Department of Exact Sciences and Technology, Universitary Center of Lagos, University of Guadalajara, Lagos de Moreno, Mexico

Section 1
