High perfection chirped grating phase masks by electron-beam definition

Abstract
A novel electron-beam exposure strategy which has been used in the fabrication of very high quality chirped fiber gratings for use as dispersion compensators is described. A key stage of the processing is the patterning and relief etching of a quartz phase mask, which by ultraviolet exposure, is used sequentially to form long lengths of continuously chirped grating on optical fiber. The use of electron lithography has been restricted by the occurrence of stitching errors which produce prohibitively large phase errors. These tend to be even more pronounced in generating chirped gratings. For practical operation errors of only a few nanometers are probably required. The measured performance of chirped fiber gratings is presented to illustrate the degree of improvement we have achieved by use of two techniques used in the electron-beam exposure of the phase mask, i.e., compensation for residual field distortion, and the delocalization of stitch error. Long chirped gratings produced in this way on a mature e-beam system at Nortel Networks have demonstrated enhanced performance, while similar devices produced by Leica Microsystems on a state-of-the-art machine provided a significantly closer approximation to a perfectly chirped grating.

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