ABSTRACT
That refractive index variation patterns (i.e., gratings) can be formed in optical fibers was discovered and reported by Hill et al. in 1978 [1]. After Meltz et al. devised a controllable and effective method for fabricating the fiber gratings by side-illuminating optical fibers with a UV laser [2], intensive studies on the fabrication and application of the devices for optical communications and optical fiber sensors began. Today, fiber gratings are generally made by the side-illumination method using KrF lasers or frequency-doubled argon ion lasers. The intensity variation patterns, which are required to write gratings in fibers, are made by interference using a phase mask method or a holographic method or by scanning the laser beam over the fibers with intensity modulation. Detailed discussions on the fabrication methods and principles can be found in many references, including that by Othonos and Kalli [3].
