Preface

This book reviews recent developments in optical interferometry (OI) techniques and aids readers in their exploration of different aspects of this subject. The focus of the novel reports presented in this volume ranges from traditional topics to newer applications, such as those related to biology and clinical procedures. Each chapter includes an introduction providing the reader with relevant background material.

Chapter 1 serves as a brief introduction to the subject, highlighting the rapidly expanding nature of the technique. Chapter 2 introduces the concept of integrated optics and photonics in sensing applications, with specific reference to IO devices. Chapter 3 focuses on the engineering aspect of OI techniques and discusses a novel 2D phase reconstruction method for the measurement of plasma properties where the signal-to-noise ratio is unstable. Chapter 4 highlights fiber-optic applications in tunable filters and sensors using a fiber Bragg grating. Application areas are extended to optically active materials in Chapter 5, where the authors note recent developments and the importance of polarization-based OI techniques applied to food components. Chapter 6 presents a general overview of interferometric gravitational wave detectors.

I would like to thank all the contributors to this book for sharing their knowledge and expertise with us. I am very grateful to Ms. Sara Debeuc of IntechOpen for all her help and support. I hope this book helps readers to realize the powerful and versatile techniques and applications related to OI.

> **Mithun Bhowmick** Mathematical and Physical Sciences, Miami University, Middletown, USA

**1**

**Chapter 1**

Applications

on if the frequency has changed in the process.

*Mithun Bhowmick*

**1. Introduction**

Introductory Chapter: Optical

Interferometry in Interdisciplinary

Optical interferometry (OI) involves the superposition of electromagnetic waves

Likewise, interferometers could be classified into major groups. Most OI devices that are being discussed here are double-path interferometers, where the signal and reference beams travel along distinct paths before recombining. A common path interferometer is,

Interferometry resulting from electromagnetic waves has been used in many routine applications. One of the most popular methods in OI involves the superposition

as their name suggests, example where the two beams travel the same paths.

**2. Typical applications of OI in science and engineering**

to form interference fringes where tiny changes in optical path difference cause significant variation in the intensity pattern of the detected light. The precision and flexibility associated with modern-day interferometric techniques have enabled researchers to apply them to a wide range of applications for solving problems related to science and engineering [1–7]. In the recent years, applications have become more sophisticated. For example, optical interferometric methods are now useful for detecting early chemistry, to analyze 3D surface topography, in biosensing, and in several topics related to investigate the matter under extreme conditions [6–10]. The use of OI in astronomy should be mentioned separately due to the volume of research that has been reported over the last few decades [11]. In this chapter, a brief overview on interferometric applications will be presented. The focus will be on the most recent advances from several fronts of science and engineering to note the width of applications where OI techniques have been relevant. The examples are by no means exhaustive due to the limited scope of this chapter. The mentions here serve only pointers for future discussions or an extended review on the state-of-the-art of OI techniques. In most simple terms, in OI, a coherent light beam is split into two using a beam splitter. The two beams cover different trajectories, commonly known as "paths" in optics before superposing to create interference fringes. The fringes or intensity patterns depend on phase differences between the two beams, resulting from the different lengths of the paths taken by them. Classification of interferometers could be done in many ways, depending on the focus and purpose. If the carrier frequency is of importance, two major groups named homodyne and heterodyne could be mentioned based
