Patent ID: 7110644

Claim:
A method of forming a gain flattening filter in an optical fiber, comprising: providing an optical fiber having a photosensitive core; providing a target spectrum to be matched by the gain flattening filter; determining the parameters of the gain flattening filter necessary to provide a spectrum to match the target spectrum; forming a plurality of gratings in the photosensitive core of the optical fiber in accordance with the determined parameters, each grating have the same spatial period, and each grating being separated from an adjacent grating by an interval having a length of less than ten spatial periods; analyzing the spectrum to determine if it matches the target spectrum within a selected range, and, if the spectrum does not match the target spectrum with the selected range, determining at least one interval to be illuminated with ultraviolet light to alter an optical length of the determined at least one interval, and exposing the determined at least one interval to ultraviolet light to alter the optical length of the at least one interval.