Fiber Bragg Gratings


Book Description

A history of FBG device development -- Fiber Bragg grating theory and models -- How to set up a fiber Bragg grating laboratory -- Inscribing fiber Bragg gratings in optical fibers -- Calibrating fiber Bragg gratings for temperature and strain -- Encapsulation and bonding -- Compensation of induced thermal effects -- Structural health monitoring with fiber Bragg gratings -- Temperature measurements -- Measurement of the coefficient of thermal expansion of materials / Leandro Alves Garção and Marceli Nunes Gonçalves -- Measuring strain and displacement -- Voltage measurement / Marceli Nunes Gonçalves -- Interrogation techniques of fiber Bragg gratings -- Current measurements -- Gas measurements / Bruno Cerqueira Rente Ribeiro.







Isolation of Thermal and Strain Responses in Composites Using Embedded Fiber Bragg Grating Temperature Sensors


Book Description

In this research, fiber Bragg grating (FBG) optical temperature sensors are used for structural health monitoring of composite materials. The specific goal is to detect the thermal response of a composite to high energy radiation incident on the surface of a composite structure. FBG sensors also respond to axial strain in the optical fiber, thus any structural strain experienced by the composite is also detected. Consequently, this research has focused both on identifying the unique characteristics of each response and on developing feasible methods to isolate the thermal response from the strain response. Isolation ensures that any response to mechanical strain does not mask the response to a temperature gradient present on the composite surface. The isolation strategy developed in this research is characterized by two design features. First, a three-dimensional array of FBG temperature sensors has been embedded in a carbon/epoxy composite structure, consisting of both in-plane and through-thickness sensor arrays. This architectural design component exploits the spatial differences between the temperature profile and the strain profile in a composite structure. Second, an accompanying data processing scheme has been developed that uses the statistical properties of the collected sensor data to interpret and identify each response. The degree to which the isolation strategy increases the functionality of FBG temperature sensors in mechanically strained composite structures is assessed.







Fiber Bragg Gratings


Book Description

Provides an overview of Fiber Bragg Gratings (FBGs), from fundamentals to applications Evaluates the advantages and disadvantages of particular applications, methods and techniques Contains new chapters on sensing, femtosecond laser writing of FBGs and poling of glass and optical fibers Includes a special version of the photonic simulator PicWave(tm), allowing the reader to make live simulations of many of the example devices presented in the book. This fully revised, updated and expanded second edition covers the substantial advances in the manufacture and use of FBGs in the years since the publication of the pioneering first edition. It presents a comprehensive treatise on FBGs and addresses issues such as the merits of one solution over another; why particular fabrication methods are preferred; and what advantages a user may gain from certain techniques. Beginning with the principles of FBGs, the book progresses to discuss photosensitization of optical fibers, Bragg grating fabrication and theory, properties of gratings, specific applications, sensing technology, glass poling, advances in femtosecond laser writing of Bragg gratings and FBG measurement techniques. In addition to material on telecommunications usage of FBGs, application areas such as fiber lasers and sensors are addressed in greater detail. This special version of Picwave is limited to modelling only the passive fibre devices covered in this book. However the full PicWave package is capable of modelling other non-linear and active devices such as laser diodes and SOAs as discussed in Chapter 8. More information about PicWave can be found at www.photond.com/products/picwave.htm. In addition to researchers, scientists, and graduate students, this book will be of interest to industrial practitioners in the field of fabrication of fiber optic materials and devices. Raman Kashyap, Canada Research Chair holder on Future Photonics Systems, and Professor at École Polytechnique, University of Montréal since 2003, has researched optical fibers and devices for over 30 years. He pioneered the fabrication of FBGs and applications in telecommunications and photonics. Provides an overview of Fiber Bragg Gratings (FBGs), from fundamentals to applications Evaluates the advantages and disadvantages of particular applications, methods and techniques Contains new chapters on sensing, femtosecond laser writing of FBGs and poling of glass and optical fibers Includes a special version of the photonic simulator PicWave(tm), allowing the reader to make live simulations of many of the example devices presented in the book







Application of a Fiber Optic Distributed Strain Sensor System to Woven E-glass Composite


Book Description

A distributed strain sensing system utilizing a series of identically written Bragg gratings along an optical fiber is examined for potential application to Composite Armored Vehicle health monitoring. A vacuum assisted resin transfer molding process was used to fabricate a woven fabric E-glass/composite panel with an embedded fiber optic strain sensor. Test samples machined from the panel were mechanically tested in 4-point bending. Experimental results are presented that show the mechanical strain from foil strain gages comparing well to optical strain from the embedded sensors. Also, it was found that the distributed strain along the sample lenght was consistent with the loading configuration.




Efficient Simulation of Bragg Grating Sensors for Implementation to Structural Health Monitoring of Composites


Book Description

The goal of a structural health monitoring system is to detect, locate, and identify damages in a structure during its lifetime. The concept of structural health monitoring is particularly important for fiber reinforced composites due to the complexity of the possible failure mechanisms. The goal of this thesis is to simulate the response of optical fiber Bragg grating sensors to multi-component loading for their implementation in structural health monitoring algorithms for composites. A simulation method is presented to determine the effects of axial, bending and shear loading on an embedded optical fiber Bragg grating sensor. The effect of fiber bending on the Bragg grating sensor is experimentally verified by embedding the sensor in a solid cone, clamped at the base and subjected to a point load at the apex. Next, a numerically efficient method to calculate the response of sensors embedded in a unidirectional composite is developed using both finite element analysis and optimal shear-lag theory and taking into account the above effects. The limitations of the optimal shear-lag theory are derived through comparison with the finite element results. The application of this method is demonstrated through a numerical example, simulating the response of sensors embedded in one fiber layer to a transverse crack. This work is a first step towards the development of embedded sensors for fiber-reinforced composites that are "self evaluating."




Polymer Optical Fibres


Book Description

Polymer Optical Fibres: Fibre Types, Materials, Fabrication, Characterization, and Applications explores polymer optical fibers, specifically their materials, fabrication, characterization, measurement techniques, and applications. Optical effects, including light propagation, degrading effects of attenuation, scattering, and dispersion, are explained. Other important parameters like mechanical strength, operating temperatures, and processability are also described. Polymer optical fibers (POF) have a number of advantages over glass fibers, such as low cost, flexibility, low weight, electromagnetic immunity, good bandwidth, simple installation, and mechanical stability. Provides systematic and comprehensive coverage of materials, fabrication, properties, measurement techniques, and applications of POF Focuses on industry needs in communication, illumination and sensors, the automotive industry, and medical and biotechnology Features input from leading experts in POF technology, with experience spanning optoelectronics, polymer, and textiles Explains optical effects, including light propagation, degrading effects of attenuation, scattering, and dispersion