Method of making an optical fiber grating, and article made by the method

Method of making an article comprising an optical fiber refractive index grating, the method comprising

• a) providing a sensitizer-loaded silica-based optical fiber having a Ge-doped core and a longitudinal axis;
• and
• b) exposing the optical fiber to actinic radiation of varying intensity along the longitudinal axis of the optical fiber, the varying intensity selected such that the refractive index grating is formed in the core;
• c) the optical fiber is exposed to the actinic radiation through a fiber coating;
• and
• d) the optical fiber is selected to have a germanium-oxygen deficiency center content selected to provide the fiber with a photosensitivity that is at least twice as large as the photosensitivity of an otherwise identical, conventionally prepared, optical fiber, where "photosensitivity" is .DELTA.n/dose of actinic radiation, where An is the refractive index change that results from exposure of the fiber to a predetermined dose of the actinic radiation, and where the conventionally prepared optical fiber is an optical fiber that was drawn from a preform that was prepared by a method that did not comprise a step during which germanosilicate preform material is contacted with an atmosphere selected to favor reduction of Ge.sup.4 + to Ge.sup.2 + in the preform material.