Fiber Bragg Grating Sensors

Authored by: David Webb

Handbook of Optical Sensors

Print publication date:  October  2014
Online publication date:  October  2014

Print ISBN: 9781439866856
eBook ISBN: 9781439866863
Adobe ISBN:

10.1201/b17641-21

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Abstract

An optical fiber Bragg grating (FBG) usually takes the form of a spatially periodic modulation of the refractive index along the core of a section of optical fiber. As we shall see, such a structure has the property of reflecting light of essentially one wavelength determined by the period of the modulation and the mean index of the fiber. Periods of around half a micron reflect light in the important 1550 nm spectral window of silica optical fiber. Such devices have found numerous applications in optical communications systems, for example, as add-drop multiplexers, dispersion compensators, or gain equalizers (Giles 1997). However, the focus of this chapter is on sensing applications, where the key point is that the reflected wavelength—the Bragg wavelength—is found to depend on the temperature of the fiber or any strain to which the fiber is subjected. Thus, by illuminating the fiber with light of a broadband spectrum and measuring the wavelength reflected by the grating, it is possible to infer what is happening to the fiber in the region of the grating.

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