Preface

I have been involved in the research field of fiber optics for more than 15 years by working in all fiber lasers, all-optical signal processing, etc. Therefore, and considering that the field of optical fibers is within my research area of expertise, I accepted the very kind invitation of the IntechOpen editorial house to edit a book in this special field. Today, it is a great honor and pleasure for me to introduce this new book: *Applications of Optical Fibers for Sensing*. This is my third collaboration as book editor with IntechOpen after the successful experiences of *Applications of Digital Signal Processing* (2011) and *Current Trends in Short- and Long-Period Fiber Gratings* (2012). I truly hope that this new book will also be successfully received by the worldwide scientific community.

In this book the reader will find a collection of chapters written by different experts around the world, covering the broad field of sensing of different parameters through optical fibers. The main goal of this book is to give an updated overview of the current research trends in this rapidly evolving field.

First, in Chapter 2, "Minimalist Approach for the Design of Microstructured Optical Fiber Sensors," J.H. Osório and C.M.B. Cordeiro from Brazil report on the utilization of capillary-like fibers of different kinds as platforms for the realization of sensing measurements. These authors show that external stimuli can alter fiber wall thickness and/or induce birefringence variations, which in turn allows its use as a pressure sensor, temperature sensor, or refractive index sensor. Next, in Chapter 3, "Fiber Bragg Gratings as e-Health Enablers: An Overview for Gait Analysis Applications," M.F. Domingues et al. from Portugal and Spain report on the use of fiber Bragg gratings for gait analysis monitoring, i.e. the monitoring of plantar pressure, angle, and torsion, with the purpose of future integration in rehabilitation exoskeletons and for prosthetic control.

In Chapter 4, "Distributed, Advanced Fiber Optic Sensors," S. Kher and M.K. Saxena from India report on several optical fiber sensing techniques such as Raman scattering and fiber Bragg gratings, to be applied especially in the context of nuclear plant monitoring. In Chapter 5, "Real-Time Particle Radiography by Means of Scintillating Fibers Tracker and Residual Range Detectors," D. Lo Presti et al. from Italy report in detail on the construction and characterization of a charged particle imaging system by using scintillating optical fibers.

In Chapter 6, "Review of Liquid-Filled Optical Fibre-Based Temperature Sensing," F. McGuinness et al. from Ireland review on the current state of the art in liquidfilled optical fibre temperature sensing, with the focus on high-resolution temperature sensing. In Chapter 7, "Optical Fibre Long-Period Grating Sensors Operating at and around the Phase Matching Turning Point," R.Y.-N. Wong et al. from Singapore and the United Kingdom report on the behavior and potential uses for fiber optic sensing of a very special type of very sensitive long-period fiber grating: those working at (and around) the phase matching turning point.

**II**

**Chapter 8 137**

Whispering Gallery Modes for Accurate Characterization of Optical Fibers'

*by Martina Delgado-Pinar, Xavier Roselló-Mechó, Emmanuel Rivera-Pérez,* 

*Antonio Díez, José Luis Cruz and Miguel V. Andrés*

Parameters

Finally, in Chapter 8, "Whispering Gallery Modes for Accurate Characterization of Optical Fibers' Parameters," M. Delgado-Pinar et al. from Spain review the use of a special technique to measure temperature profiles along conventional and special fibers (such as photosensitive or doped fibers), elasto-optic coefficients, and ultraviolet-induced absorption loss coefficients of different photosensitive fibers. This technique makes use of whispering gallery modes, which are resonant in optical wavelength; being their spectral position a function of the radius and the refractive index of the microresonator material. Due to the high-quality factor of these resonances, they allow different parameters with high sensitivities and very low detection limits to be measured.

I would like to thank all the authors for their contributions, since their support has been crucial for the fulfillment of this project. In addition, I would like to thank the IntechOpen editorial staff for the confidence placed in me to edit this book, and especially to IntechOpen's Author Service Manager Sara Debeuc for her support during the whole process. On behalf of myself and the authors, we hope readers enjoy this book and benefit from its content, which provides a thorough understanding of several fields related to this exciting discipline.
