High perfection chirped grating phase masks by electron-beam definition

A novel electron-beam exposure strategy which has been used in the fabricat ion of very high quality chirped fiber gratings for use as dispersion compe nsators is described. A key stage of the processing is the patterning and r elief etching of a quartz phase mask, which by ultraviolet exposure, is use d sequentially to form long lengths of continuously chirped grating on opti cal fiber. The use of electron lithography has been restricted by the occur rence of stitching errors which produce prohibitively large phase errors. T hese tend to be even more pronounced in generating chirped gratings. For pr actical operation errors of only a few nanometers are probably required. Th e measured performance of chirped fiber gratings is presented to illustrate the degree of improvement we have achieved by use of two techniques used i n the electron-beam exposure of the phase mask, i.e., compensation for resi dual 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 c loser approximation to a perfectly chirped grating. (C) 1999 American Vacuu m Society. [S0734-211X(99)15106-0].