Structure of Fiber Bragg Gratings (FBGs). 1) a uniform FBG, where the refractive index change has a fixed period, ${\displaystyle \Lambda }$. 2) a chirped FBG, where the refractive index change is graded to give a larger bandwidth, ${\displaystyle \Delta \lambda }$. 3) a tilted FBG, where the change in refractive index occurs are an angle to the optical axis of the fiber. 4) a superstructure FBG.

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