The Fibre Bragg Grating (FBG) works on the principle that a UV laser shining
on a coating-stripped fibre can induce refractive index modulation of the fibre
core. These changes, through the use of phase or amplitude masks, can be designed
and the masks fabricated to a required specification.
The way that light behaves when it comes to these
sections of fibre is dictated by the spacing between each refractive index interface
and the effective refractive index of the fibre core. Light of a particular wavelength
is reflected from these interfaces and it is possible to measure this wavelength.
When there is a change in the environment that the fibre is in there will be a resulting
shift of this wavelength, for example when a strain is imparted onto the fibre.
Through calibration this shift can be related back to the parameter that is under
investigation, such as strain,