High performance analog profile diffractive elements

Technologies generally used for fabrication of kinoform diffractive optics include, direct writing, plastic molding, diamond turning, and photolithography. Photolithographic methods (either contact or projection) are generally suitable for mass production in glass. Two types of masks are used with photolithographic methods; binary chrome masks and gray scale masks. Contact lithography with binary chrome masks generally limits minimum features sizes, and thus minimum zone widths, due to performance degradation from alignment errors between multiple masks. For example, the minimum zone width of a high efficiency eight-level kinoform is eight times the minimum feature size. Alternatively, gray scale mask technology uses a single mask which eliminates the alignment error problems. Smooth profile (not stair-stepped) high efficiency kinoform zones as small as three microns have been fabricated with this technology. In this paper we report on a direct experimental comparison of costs and performance for a blazed grating with 6-micron zones fabricated with multiple binary chrome masks and a single gray scale mask.