A micro-optical element that is a combination of a phase diffraction grating and a convex lens will disperse and focus light of different wavelengths that fall on it. Such a device can be fabricated using binary optics technology to create a multilevel structure that approximates the element. The performance of this multilevel dispersive microlens depends on design parameters such as the grating period and the f-number of the lens. The performance also depends on the resolution used in the fabrication of the element (feature sizes and etching depths). We present a study of how these design parameters and resolution requirements affect performance characteristics of the element, such as diffraction efficiencies, blur spot sizes, and wavelength dispersion.

The analysis of the performance of a binary optical element requires a physical optics calculation because of the diffractive nature of such elements. We have developed a number of software tools for this analysis, which are based on the Kirchhoff-Fresnel diffraction integral. These tools allow investigation of results of diffraction both in and out of the focal plane. The programs take a given (nonbinary) element, convert it to a binary element with prescribed etching resolutions and etching depths, and perform the diffractive calculation. The diffraction is calculated by a number of means (direct numerical integration, Fresnel approximation, evaluation of analytic formulas). The software also computes quantitative measures of performance, such as blur spot sizes, diffraction efficiencies, and wavelength separation (for dispersive elements). We discuss the abilities and limitations of the codes and present sample calculations.

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