Design concepts for broadband high–efficiency DOEs

Abstract

Several design–concepts are presented for so–called efficiency achromatized diffractive optical elements (EA–DOEs) possessing a diffraction efficiency larger than 97% over a broad spectral range. We start with tracing two different methods for surface relief profiles well known from the literature: common depth and multilayer EA–DOEs. Successively we present the following new approaches together with design parameters and performance properties: 1) gradient–index EA–DOEs, 2) sub–wavelength EA–DOEs, and 3) a so–called cut–and–paste strategy. All designs are based on scalar assumptions and certain necessary dispersion relations of two different materials. The scalar assumption is no real limitation as the minimum zone width of our main application, the correction of chromatic aberrations, is 50 … 100 times the wavelength. From aforementioned relations, design parameters as profile heights are derived and the resulting diffraction efficiency can be deduced. Moreover, for the multilayer and for the GRIN EA–DOEs we are able to show that if the dispersion relations of the materials can be accurately described by second order Cauchy series, the efficiency becomes generic and will be the same regardless of which materials are chosen.

Keywords

• diffractive optical element
• achromatization
• broadband
• high efficiency