Table of Contents

1 Introduction

1.1 Initial Concepts

2 History of FBG Device Development

2.1 Introduction

2.2 Historical Perspective

2.3 A Glimpse of Applications

2.4 Conclusions

References

3 Fiber Bragg Grating Theory and Models

3.1 Introduction

3.2 Fiber Bragg Grating Models

References

4 How to Set Up a Fiber Bragg Grating Laboratory

4.1 Introduction

4.2 Taking the First Step: The Laser

4.3 Cooling System

4.4 Nitrogen and Hydrogen

4.5 Optical Parts and Mounts

4.6 Instruments and Measurement Devices

4.7 Conclusions

References

5 Inscribing Fiber Bragg Gratings in Optical Fibers

5.1 Introduction

5.2 Inscribing Fiber Bragg Gratings with Phase Masks in Close Proximity to the Optical Fiber

     5.2.1 The +1/-1 configuration

     5.2.2 The 0/-1 configuration

5.3 Inscribing Fiber Bragg Gratings with Phase Masks and Mirrors

5.4 Conclusions

References

6 Interrogation Techniques of Fiber Bragg Gratings

6.1 Introduction

6.2 Basic Demodulation Scheme for Laboratories

6.3 Commercial Equipment for Fiber Bragg Grating Demodulation

6.4 Edge Filter Technique

6.5 Twin FBG Technique

6.6 Tunable Laser Approach

6.7 WDM Demodulation Scheme

References

7 Calibrating Fiber Bragg Gratings for Temperature and Strain

7.1 Introduction

7.2 First Steps

7.3 Temperature Calibration

7.4 Calibration in Strain

References

8 Encapsulation and Bonding

8.1 Introduction

8.2 Properties of Silica Optical Fibers

8.3 FBG Properties

8.4 FBG Protection and Encapsulation

8.5 Bonding

References

9 Compensation of Induced Thermal Effects

9.1 Introduction

9.2 Using an Additional Fiber Bragg Grating for Temperature Compensation

9.3 Applying Two Fiber Bragg Gratings in Opposite Conditions

9.4 Passive Compensation

9.5 Dynamic Temperature Compensation

References

10 Structural Health Monitoring with Fiber Bragg Gratings

10.1 Introduction

10.2 Hull Monitoring

10.3 FBGs in Railway Monitoring

10.4 Dam Monitoring

10.5 Dyke Monitoring

10.6 Monitoring Pipelines

10.7 FBGs in Bridge Monitoring

10.8 Monitoring the Condition of Rotating Machinery

References

11 Temperature Measurements

11.1 Introduction

11.2 Samuel Hydroelectric Power Plant

11.3 Installation of FBG Sensors to Measure Temperature in a Hydroelectric Generator

11.4 Temperature Monitoring Results

11.5 Local Recalibration of the FBG Temperature Sensors

11.6 Conclusion

References

12 Measurement of the Coefficient of Thermal Expansion of Materials

Leandro Alves Garção and Marceli Nunes Gonçalves

12.1 Introduction

12.2 FBG Bonding Procedure

12.3 Experimental Procedure

12.4 Experimental Results

12.5 Discussion

12.6 General CTE Measurement

12.7 Conclusion

References

13 Measuring Strain and Displacement

13.1 Introduction

13.2 The Spring Method

13.3 The Cantilever Method

13.4 Conclusion

References

14 Voltage Measurement

14.1 Introduction

14.2 Bragg Wavelength Displacement as a Function of Mechanical Strain

14.3 DC Measurements

     14.3.1 Electric setup

     14.3.2 Theoretical model of FBG displacement as a function of voltage application

14.4 Mechanical Setups for FBG-PZT DC Measurements

     14.4.1 FBG wound around a PZT tube

     14.4.2 FBG fixed laterally to the PZT tube

     14.4.3 Mechanical amplifier

     14.4.4 Tests with a PZT stack

     14.4.5 Conclusions of the DC experiments

14.5 AC Measurements

     14.5.1 Temperature compensation

     14.5.2 Maximum voltage

     14.5.3 Capacitive divider

     14.5.4 Theoretical model of the transducer sensitivity

     14.5.5 Results for the application of 13.8 kVrms

14.6 Conclusion

References

15 Current Measurements

15.1 Introduction

15.2 Optical Fibers in Current-Measurement Systems: A Preliminary Approach

15.3 Fiber Bragg Gratings in Current-Measurement Systems: The Use of Magnetostrictive Materials

15.4 Designing an Opto-magnetostrictive Current-Measurement Device

     15.4.1 The first approach concerning the opto-magnetostrictive current-measurement device

     15.4.2 An optimized opto-magnetostroctive current sensor

     15.4.3 Discussing the results

15.5 Conclusion

References

16 Gas Measurements

Bruno Cerqueira Rente Ribeiro

16.1 Introduction

16.2 Nanostructures in Gas-Measurement Systems

16.3 Fiber-Optic-Based Gas Measurement

16.4 Preparing Fiber Bragg Gratings for Gas Sensing

     16.4.1 Chemical etching

     16.4.2 Tapering

     16.4.3 D-shaped fiber

16.5 FBG Gas-Sensing Case Studies

16.6 Coated and Etched FBG Optical Effects in Fiber Sensors

16.7 Conclusion

References

Preface

The development of optical fibers has revolutionized not only telecommunications but also the way monitoring and sensing is conducted, particularly in remote or harsh environments. In this context, the discovery of photosensitivity in optical fibers led to the establishment of fiber Bragg gratings (FBGs), optical filters that have been widely employed in telecom and as measurement elements.

This Tutorial Text discusses these optical devices directly, focusing on the practical aspects and applications. It addresses the fundamental aspects of FBG operation to quickly introduce the subject to students, engineers, and laboratory technicians. Due to their inherent advantages in instrumentation, sensing, and automation systems, FBGs play an important role not only for industry professionals but also for academics. Thus, this book is primarily intended for scientists, professors, researchers, students, photonics technicians, and engineers involved in optical-fiber projects.

The chapters follow a logical sequence: after a discussion of the primary concepts, practical aspects regarding the development of a FBG laboratory and how these components are manufactured and used in practical applications are presented. The following chapters outline the operation of Bragg gratings and, for instance, discuss how measurement information can be retrieved (interrogation techniques), calibration methods, and how to prepare and deploy the devices in real monitoring conditions. The final chapters present several successful, real-world applications of the technology.

Fiber Bragg Gratings: Theory, Fabrication, and Applications delivers essential information concerning FBGs to professionals and researchers with an approach based on rules of thumb and practical aspects, enabling quick access to the main principles and techniques, and allowing readers to set up their own laboratory or application. It provides detailed information about how to operate and use these novel sensors, particularly with respect to the required infrastructure, daily operation, and possible applications. Dense physical aspects and the associated refined mathematical models are not thoroughly presented because this information can be found in other publications.

Many of the applications in this book reflect our own experience in courses, M.S. dissertations, D.S. theses, and projects at the Laboratório de Instrumentação e Fotônica (LIF) of the Universidade Federal do Rio de Janeiro. Therefore, we acknowledge our former and present students who made it possible to accomplish all of work that went into this book. We also acknowledge the contributions of the following D.S. students: Marceli Nunes Gonçalves and Leandro Alves Garção for writing Chapter 12, and Bruno Cerqueira Rente Ribeiro for writing Chapter 16.

Marcelo M. Werneck
Regina C. Allil
Fábio V. B. de Nazaré
August 2017