Handbook of Optoelectronics

Applied Optical Electronics (Volume Three)

John P. Dakin, Robert G. W. Brown

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351595599
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

Handbook of Optoelectronics offers a self-contained reference from the basic science and light sources to devices and modern applications across the entire spectrum of disciplines utilizing optoelectronic technologies. This second edition gives a complete update of the original work with a focus on systems and applications. Volume I covers the details of optoelectronic devices and techniques including semiconductor lasers, optical detectors and receivers, optical fiber devices, modulators, amplifiers, integrated optics, LEDs, and engineered optical materials with brand new chapters on silicon photonics, nanophotonics, and graphene optoelectronics. Volume II addresses the underlying system technologies enabling state-of-the-art communications, imaging, displays, sensing, data processing, energy conversion, and actuation. Volume III is brand new to this edition, focusing on applications in infrastructure, transport, security, surveillance, environmental monitoring, military, industrial, oil and gas, energy generation and distribution, medicine, and free space.

No other resource in the field comes close to its breadth and depth, with contributions from leading industrial and academic institutions around the world. Whether used as a reference, research tool, or broad-based introduction to the field, the Handbook offers everything you need to get started.

John P. Dakin, PhD, is professor (emeritus) at the Optoelectronics Research Centre, University of Southampton, UK.

Robert G. W. Brown, PhD, is chief executive officer of the American Institute of Physics and an adjunct full professor in the Beckman Laser Institute and Medical Clinic at the University of California, Irvine.

PART I

Optoelectronics in infrastructure

In this section, we present case studies of the use of optoelectronics in infrastructure. This includes applications on fixed structures, in particular, sensors located next to vital road and rail systems, civil engineering structures, such as bridges and dams, and ones built in or on the structure of buildings or their foundations. (Please note, systems and sensors intended specifically for security and surveillance purposes, for energy, for oil and gas extraction, and ones fitted to moving vehicles will be described in later application sections.)

In order to give a broader introduction to infrastructure applications than we could possibly cover with our selected case studies, we shall first present a summary table. This will give a broader overview than possible in the more specific case study chapters.

As will be the practice in most chapters in this volume, we shall then present a few more detailed case studies. Before commencing, however, it is perhaps appropriate to briefly emphasize where sensors described in this section also have crossover applications to other sections in the volume.

Chapter 1 describes various forms of optical strain sensors for highways, but similar strain sensors, particularly fiber grating types, have numerous other potential application areas, such as structural sensors in wind energy turbines, aircraft and ships, racing yacht masts, and many more.

Chapter 2 describes a distributed optical fiber acoustic/seismic sensor, which has, apart from for infrastructure, obvious applications in security and surveillance. Such sensors are currently employed extensively in the oil and gas industry, and this important application is described more fully by Andre Franzen in Chapter 20.

Chapters 3 and 4 describe camera monitors for roads. These are used for monitoring and identifying vehicles (via number plate readers or still photographs) and determining their speed and position. If the book had been structured in a different way, such sensors would have been considered to be a part of the later sections on “transport” or “security and surveillance,” but as they are fixed in location, we have chosen to describe them here.

Hopefully, the readers will appreciate that there are inevitable dilemmas of where best to describe these applications and will bear with us in our order of presenting them in the sections that follow.

Table I.1 Summary of applications of optoelectronics in the infrastructure field

1

Overview of fiber optic sensing technologies for structural health monitoring

DANIELE INAUDI

SMARTEC/Roctest

1.1 Fiber optic sensors

1.1.1 SOFO displacement sensors

1.1.2 Bragg grating strain sensors

1.1.3 Fabry–Perot strain sensors

1.1.4 Raman distributed temperature sensors

1.1.5 Brillouin distributed temperature sensors

1.2 Selected projects

1.2.1 Colle Isarco Bridge

1.2.2 Pile loading test

1.2.3 I35W Bridge, Minneapolis

1.2.4 Luzzone Dam

1.2.5 Bridge crack detection

1.2.6 Bitumen joint monitoring

1.2.7 Gas pipeline monitoring

1.3 Conclusions

Acknowledgment

References

1.1 FIBER OPTIC SENSORS

There exist a great variety of fiber optic sensors (FOSs) [1] for structural monitoring in both the academic and industrial areas. In this overview we will concentrate on fiber optic sensing systems for civil health monitoring that have reached an industrial level and have been used in a number of field applications.

Figure 1.1 illustrates the four main types of FOSs:

• Point sensors have a single measurement point at the end of the fiber optic connection cable, similar to most electrical sensors.

• Multiplexed sensors allow the measurement at multiple points along a single fiber line.

• Long-base sensors integrate the measurement over a long measurement base. They are also known as long-gauge sensors.

• Distributed sensors are able to sense at any point along a single fiber line, typically every meter over many kilometers of length

The greatest advantages of FOS are intrinsically linked to the optical fiber itself that is either used as a link between the sensor and the signal conditioner, or becomes the sensor itself in the case of long-gauge and distributed sensors. In almost all FOS applications, the optical fiber is a thin glass fiber that is protected mechanically by a polymer coating (or a metal coating in extreme cases) and further protected by a multilayer cable structure designed to protect the fiber from the environment where it will be installed. Since glass is an inert material very resistant to almost all chemicals, even at extreme temperatures, it is an ideal material for use in harsh environments such as that encountered in geotechnical applications. Chemical resistance is a great advantage for long-term reliable health monitoring of civil engineering structures, making FOSs particularly durable. Since the light confined to the core of the optical fibers used for sensing purposes does not interact with any surrounding electromagnetic (EM) field, FOSs are intrinsically immune to any EM interferences. With such unique advantage over sensors using electrical signals, FOSs are obviously the ideal sensing solution when the presence of EM, radio frequency, or microwaves cannot be avoided. For instance, FOS will not be affected by EM fields generated by lightning hitting a monitored bridge or dam, nor will they be affected by the interference produced by subway trains running near a monitored zone. FOSs are intrinsically safe and naturally explosion-proof, making them particularly suitable for monitoring applications of risky structures such as gas pipelines or chemical plants. But the greatest and most exclusive advantage of such sensors is their ability to offer long-range distributed sensing capabilities.

Figure 1.1 Fiber optic sensor types.

1.1.1 SOFO displacement sensors

The SOFO system (Figure 1.2) is a fiber optic displacement sensor with a resolution in the micrometer range and an excellent long-term stability. It was developed at the Swiss Federal Institute of Technology in Lausanne (EPFL) and is now commercialized by SMARTEC in Switzerland [2].

Figure 1.2 SOFO system reading unit.

Figure 1.3 SOFO sensor installed on a rebar.

The measurement setup uses low-coherence interferometry to measure the length difference between two optical fibers installed on the structure to be monitored (Figure 1.3). The measurement fiber is pretensioned and mechanically coupled to the structure at two anchorage points in order to follow its deformations, while the reference fiber is free and acts as temperature reference. Both fibers are installed inside the same pipe and the measurement basis can be chosen between 200 mm and 10 m. The resolution of the system is of 2 μm independently from the measurement basis and its precision is of 0.2% of the measured deformation even over years of operation.

The SOFO system has been successfully used to monitor more than 150 structures, including bridges, tunnels, piles, anchored walls, dams, historical monuments, nuclear power plants, as well as laboratory models.

1.1.2 Bragg grating strain sensors

Bragg gratings are periodic alterations in the index of refraction of the fiber core that can be produced by adequately exposing the fiber to intense ultraviolet (UV) light. The produced gratings typically have length of the order of 10 mm. If white light is injected in the fiber containing the grating, the wavelength corresponding to the grating pitch will be reflected, while all other wavelengths will pass through the grating undisturbed. Since the grating period is strain and temperature dependent, it becomes possible to measure these two parameters by analyzing the spectrum of the reflected light [3]. This is typically done by using a tunable filter (such as a Fabry–Perot cavity) or a spectrometer. Resolutions of the order of 1 με and 0.1°C can be achieved with the best demodulators. If strain and temperature variations are expected simultaneously, it is necessary to use a free reference grating that measures the temperature alone and uses its reading to correct the strain values. Setups allowing the simultaneous measurement of strain and temperature have been proposed but have yet to prove their reliability in field conditions. The main interest in using Bragg gratings resides in their multiplexing potential. Many gratings can be written in the same fiber at different locations and tuned to reflect at different wavelengths. This allows the measurement of strain at different places along a fiber using a single cable. Typically, 4–16 gratings can be measured on a single fiber line. It has to be noticed that since the gratings have to share the spectrum of the source used to illuminate them, there is a trade-off between the number of gratings and the dynamic range of the measurements on each of them.

Because of their length, fiber Bragg gratings can be used as a replacement for conventional strain gauges and installed by gluing them on metals and other smooth surfaces. With adequate packaging, they can also be used to measure strains in concrete over a basis length of typically 100 mm.

1.1.3 Fabry–Perot strain sensors

An extrinsic Fabry–Perot interferometer (EFPI) consists of a capillary silica tube containing two cleaved optical fibers facing each other, but leaving an air gap of a few microns or tens of microns between them (see Figure 1.4) [4]. When light is launched into one of the fibers, a back-reflected interference signal is obtained. This is due to the reflection of the incoming light on the glass-to-air and on the air-to-glass interfaces. This interference can be demodulated using coherent or low-coherence techniques to reco...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Series Preface
• Preface
• Introduction to the Second Edition
• Editors
• Contributors
• Part I Optoelectronics in Infrastructure
• Part II On-Vehicle Applications in Transport
• Part III Optoelectronics for Security and Surveillance
• Part IV Earth Resources and Environmental Monitoring
• Part V Military Applications
• Part VI Industrial Applications
• Part VII Oil, Gas, and Mineral Exploration and Refining
• Part VIII Applications in Energy Generation and Distribution
• Part IX Applications for Medicine, Health Monitoring, and Biotechnology
• Part X Home and Mobile Portable Equipment Applications
• Part XI Free Space Optical Communications
• Index