Novel optical fibers for the inscription of long-period gratings

In recent years rapid progress has been made in the field of long-period gratings (LPG) inscribed in optical fibers. Though in most cases LPGs in standard commercial single-mode fibers have been investigated, great effort has also been put to LPGs in experimental fibers with modified structures, whose properties can significantly differ from those of LPGs in standard fibers. This contribution deals with two novel types of optical fibers for LPG inscription. The first of them is a single-mode fiber in which the refractive index in the fiber cladding increases quadratically with radius. In the second fiber. the cladding index decreases quadratically with radius. Basic results of a theoretical analysis of LPGs inscribed in these fibers are presented along with details on the preform fabrication by the MCVD method and on fiber drawing. Examples of transmission spectra of LPGs inscribed by a focused beam of a CO, laser are given and properties of the LPGs are discussed.