Zero order suppression of a binary phase grating by an additional phase level

In recent years diffractive optical elements have been increasingly employed in practical applications [1]. Following this development, relaxing fabrication tolerances has become an important issue in widening the applicability of diffractive optics in real life scenarios. Several methods have been developed in order to achieve good optical function even with less than ideal nanostructures, but none of them have been demonstrated with binary elements. Using modern fabrication technology, high lateral precision can be consistently achieved but vertical profile errors can be more difficult to control. With binary elements this translates to an increase in the zero order efficiency, which is highly undesirable in applications such as material processing or optical interconnects. In this paper we present a design approach that can be used to suppress unwanted light in the zero order due to etch depth errors.