Optical Fibre Sensors

Fundamentals for Development of Optimized Devices

Ignacio Del Villar, Ignacio R. Matias, Ignacio Del Villar, Ignacio R. Matias

• Publisher: Wiley-IEEE Press
• Year: 2020
• Print ISBN: 9781119534761
• eBook ISBN: 9781119534792
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

The most complete, one-stop reference for fiber optic sensor theory and application

Optical Fiber Sensors: Fundamentals for Development of Optimized Devices constitutes the most complete, comprehensive, and up-to-date reference on the development of optical fiber sensors. Edited by two respected experts in the field and authored by experienced engineers and scientists, the book acts as a guide and a reference for an audience ranging from graduate students to researchers and engineers in the field of fiber optic sensors.

The book discusses the fundamentals and foundations of fiber optic sensor technology and provides real-world examples to illuminate and illustrate the concepts found within. In addition to the basic concepts necessary to understand this technology, Optical Fiber Sensors includes chapters on:

• Distributed sensing with Rayleigh, Raman and Brillouin scattering methods
• Biomechanical sensing
• Gas and volatile organic compound sensors
• Application of nanotechnology to optical fiber sensors
• Health care and clinical diagnosis
• And others

Graduate students as well as professionals who work with optical fiber sensors will find this volume to be an indispensable resource and reference.

1
Introduction

Ignacio R. Matias¹ and Ignacio Del Villar²

¹ Institute of Smart Cities, Public University of Navarre, Pamplona, Spain

² Department of Electrical, Electronic and Communications Engineering, Public University of Navarre Pamplona, Spain

The optical telegraph, invented in 1791 by Claude Chappe, consisted of a network of stations that allowed the transmission of information at a speed of one symbol in two minutes between Paris and Lille (i.e. 230 km) [1]. Each station monitored, with the aid of a telescope, the character that was represented with a wooden semaphore in the previous station. This system was widely used for about 50 years because it was much faster than sending messages by letter, but it required direct vision between each couple of consecutive stations. Consequently, bad weather, or simply the night, prevented its utilization. These are the main reasons why with the invention of the electrical telegraph, a system based on a guided electrical signal, the utilization of the optical telegraph came soon to an end.

However, in parallel to the invention of the electrical telegraph, in 1841, the path towards optical guiding was started with an important discovery by two French researchers, Jean Daniel Colladon and Jacques Babinet, who independently demonstrated that it was possible to guide light in a curved waveguide [2]. Colladon proved this with light rays trapped in a water jet by total internal reflection, whereas Babinet did the same in a bent glass rod.

Another breakthrough occurred in 1966, when Charles Kao (he received the Nobel Prize in Physics in 2009) and George Hockham published a work demonstrating that the attenuation in optical fibres available at the time was caused by impurities, rather than fundamental physical effects such as scattering. They pointed out that fibres with low loss could be manufactured by using high‐purity glass [3, 4]. This idea was proved in the North American company Corning in 1970, with the development of an optical fibre with losses lower than 20 dB/km. Soon afterwards, in 1977, losses were reduced to such a point that General Telephone and Electronics could carry live telephone traffic, 6 Mbit/s, in Long Beach, California, whereas the Bell System could transmit a 45 Mbit/s fibre link in the downtown Chicago phone system. Since that year optical fibre has become the most widely used guided medium in the twentieth century, mainly thanks to the huge bandwidth it presents compared with other guided communication media such as twisted pair and coaxial cable.

Optical communication is the main application of optical fibre. However, there is a second domain where this structure can be used: sensors. Despite the impact of optical fibre in the domain of sensors not being as big as in communications, their presence in the global market cannot be neglected. Indeed, it is the natural and ideal platform in terms of integrating the sensor in the communication system.

Optical fibre sensors (OFSs) can be classified in many different ways. The main classification concerns to the location where the light is modulated, existing in two groups: extrinsic and intrinsic OFSs. In both cases there is a parameter (physical, chemical, biological, etc.) that modulates light. However, the difference is that in an extrinsic OFSs light is guided to the interaction region, extrinsic to the optical fibre, where light is modulated, and after this modulation light is collected again in the optical waveguide, whereas in an intrinsic OFS light is always guided by the optical fibre. In Figure 1.1 the difference between an intrinsic and an extrinsic OFS is shown. In the case of an extrinsic sensor, light is modulated outside of the fibre by a liquid (its properties may change as a function of temperature, for instance), whereas in the case of the intrinsic sensor, a fibre has been spliced to two other fibres (one input and one output fibre), which allows an enhanced interaction with the outer medium. In this case, a liquid modulates the light at the same time it is being transmitted through the fibre.

Figure 1.1 (a) Extrinsic sensor: light is modulated outside of the fibre. (b) Intrinsic sensor: light is modulated while it is transmitted through the fibre.

Probably the first OFS was the fibrescope. In 1930 Heinrich Lamm, a German medical student, assembled a bundle of optical fibres to carry an image. His purpose was to use the device for obtaining images of inaccessible parts of the body. He tried to patent the device, but John Logie Baird and Clarence W. Hansell had patented a similar idea some years before. The quality of the images that Lamm obtained was not good, but he is the first researcher that experimentally achieved this breakthrough in the history of optical sensors. Afterwards, in 1954, the Englishman Harold H. Hopkins and the Indian Narinder S. Kapany presented results of better quality on the same principle [5].

Some years later, in 1967, the first effective demonstration of a fibre‐optic sensor, the Fotonic sensor, was published [6]. The device was also based on a fibre bundle. However, this time the arrangement was different. Some of the fibres emitted light, and some others did not. The fibre bundle illuminated a surface in front of the fibre, and some part of light was coupled to the fibres that did not transmit light. The amount of light reflected back depended on the distance between the fibre bundle end and the surface. Consequently, the device could be used as a displacement sensor (Figure 1.2).

This type of sensor was the basis for the commercialization of the MTI Fotonic sensor. In the 1980s, the MTI 2000 version allowed monitoring vibration and displacement. Nowadays it is still sold under the version MTI 2100, which is the same concept but with improved characteristics such as the ability to operate in cryogenic, vacuum, high pressure, or in high magnetic field and harsh environments. The resolution has also been improved from 1 nm in the MTI 2000 to 0.25 nm with the MTI 2100 and frequency response from direct‐coupled (dc) to 150 kHz in the MTI 2000 up to dc‐500 kHz in the MTI 2100.

The concept used in the Fotonic sensor was also the basis for detection of intracranial pressure by using a surface that is a diaphragm that can be deformed by the action of pressure. Depending on the pressure, the surface is deformed, and in this way, the light coupled back to the receiving fibre is modulated. The c...

Table of contents

• Cover
• Table of Contents
• Title Page
• Optical Fibre Sensors
• Copyright
• List of Contributors
• Acknowledgment
• About the Editors
• 1 Introduction
• 2 Propagation of Light Through Optical Fibre
• 3 Optical Fibre Sensor Set‐Up Elements
• 4 Basic Detection Techniques
• 5 Structural Health Monitoring Using Distributed Fibre‐Optic Sensors
• 6 Distributed Sensors in the Oil and Gas Industry
• 7 Biomechanical Sensors
• 8 Optical Fibre Chemical Sensors
• 9 Application of Nanotechnology to Optical Fibre Sensors
• 10 From Refractometry to Biosensing with Optical Fibres
• 11 Humidity, Gas, and Volatile Organic Compound Sensors
• 12 Interaction of Light with Matter in Optical Fibre Sensors
• 13 Detection in Harsh Environments
• 14 Fibre‐Optic Sensing
• Index
• IEEE Press Series on Sensors
• End User License Agreement