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Fiber Bragg Grating




Fiber Bragg Gratings are created by burning or "writing" a periodic variation in the index of refraction into the core of an optic fiber using an intense UV source such as a UV laser and a photomask having the intended grating features. The fiber is normally made receptive to the UV burning by manufacturing it with a few percent of germanium or by later diffusion of hydrogen to make it receptive to the UV burning.

The grating will typically have a sinusoidal index variation over a defined length. The pattern may be modified to add other features such as apodization of the reflected light spectral peak or a linear variation in the grating period called a chirp to broaden the reflected spectrum. The reflected wavelength = 2 x grating pitch x refractive index.

These grating are finding a use in instrumentation applications such as Seismology for measurement of the effects of external pressure and temperature on the fibre optic cable.