chapter 1 - Bentham Science

218 Fiber Bragg Grating Sensors: Recent Advancements, Industrial Applications and Market Exploitation, 2011, 218-237
Fiber Bragg Grating Sensors in Nuclear Environments
Francis Berghmans 1,2,* and Andrei Gusarov 2
Andrea Cusano, Antonello Cutolo and Jacques Albert (Eds)
All rights reserved - © 2011 Bentham Science Publishers Ltd.
CHAPTER 12
1 Department of Applied Physics and Photonics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium and
2 SCK·CEN Belgian Nuclear Research Center, Boeretang 200, 2400 Mol, Belgium
Abstract: Fiber Bragg Grating sensors are evaluated for applications in environments where the presence of
highly energetic radiation is a concern, such as space and nuclear industry. To assess the feasibility of using this
sensor technology in these particular application environments it is essential to evaluate the behavior of Fiber
Bragg Gratings when exposed to different types of ionizing radiation. We, therefore, review the effects of
ionizing radiation on several types of Fiber Bragg Gratings.
INTRODUCTION
Nuclear radiation effects on optical materials and photonic devices have been studied since several decades. In the
early days one of the main concerns was to determine whether advanced technologies could withstand military and
tactical environments such as surveillance satellite missions and nuclear weapon explosions. Today many other
applications associated with presence of highly energetic radiation can benefit from the enhanced functionalities
offered by photonic technologies for communication and sensing. Examples of these application fields include
space, healthcare, civil nuclear industry and high energy physics experiments. Future thermonuclear fusion plasma
reactors will also rely on optical communication and sensing techniques.
Electronic and photonic components are well known to suffer from exposure to nuclear radiation [1]. The radiation
interacts with the materials and alters their characteristics. This most often modifies the performance and affects the
reliability of the device. Resulting device failures and system malfunctions may have dramatic consequences on
safety and carry significant financial repercussions. One has to bear in mind that human intervention to replace
components or to repair systems in radiation environments is mostly impossible due to the radioactivity levels
involved or for reasons of accessibility. It is indeed almost impossible to repair onboard equipment once a satellite
has been put into orbit. One can hence understand the importance of carefully investigating how radiation affects the
operation and the reliability of photonic components intended for use in these harsh environments and of ensuring
that devices and systems will survive the entire mission.
Several years ago optical fibers carried a relatively bad reputation in terms of resistance to ionizing radiation. The
fibers were indeed known to darken rapidly during exposure with substantial levels of so called radiation induced
attenuation (RIA) as a result. Modern fiber fabrication technologies now allow obtaining fibers with low to moderate
levels of RIA, depending on the wavelength range. This together with the undeniable and well-known advantages of
fiber optic technology and the increased availability of compact, efficient and lower cost devices promoted renewed
interest in the applications of optical fiber based systems in radiation environments.
A fiber Bragg grating (FBG) is a typical example of a versatile photonic component that can be applied in both
optical communication and sensing systems. FBGs are for example being considered as sensor elements for
structural health monitoring of spacecrafts and as dosimeter in nuclear facilities. Both types of applications put
entirely different demands on the FBGs: for the first application the gratings should be insensitive to radiation
whereas for the second they should essentially be as sensitive as possible.
The response of different types FBGs to various kinds and intensities of highly energetic radiation has therefore been
the subject of many studies in the last decade. This chapter intends to review the main results obtained so far. Since
radiation environments bring along considerably different environmental constraints from those conventionally
*Address correspondence to this author Professor Francis Berghmans: Department of Applied Physics and Photonics, Vrije Universiteit
Brussels, Pleinlaan 2, 1050 Brussels, Belgium; Tel: +32 2 629 34 53; Fax: +32 2 629 34 50; Email: fberghma@vub.ac.be