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.

Comparison of electromagnetic and scalar methods for evaluation of efficiency of diffractive lenses for wide spectral bandwidth

“…1) [3,12]. Such a microstructure composed of two commercially available optical plastics, polymethylmethacrylate (PMMA) and polycarbonate (PC), provides almost complete suppression of the spectral DE dependency in a wide spectral range of λ μ ≤ ≤ μ 0.4 m 0.7 m at a constant value of the angle of incidence.…”

Spectral diffraction efficiency characterization of broadband diffractive optical elements.

“…shows an example of a non-optimal but illustrative design showing two peaks in the diffraction efficiency of the multi-layer element. The red curve is the calculated efficiency using the dispersion of fused silica and calcium fluoride, the black curve comes from a derived equation 1 that is independent of the material. The example in Figure 7, however, requires diffractive elements with depths greater than 40 microns.…”

Fabrication of Binary Diffractive Lens on Optical Films by Electron Beam Lithography

“…Although the binary diffractive lens was effective in controlling the luminous intensity, diffraction efficiency was reduced when the diffraction angle was decreased Kleemann et al, 2008). Furthermore, the focal length of the fabricated binary diffractive lens is 2 mm.…”

“…Furthermore, in the case of photolithography, combining some masks is not necessary. By using these structures, achromatized diffractive lenses were reported (Kleemann et al, 2008). We aim to realize a highly effective short focal length diffractive lens using the binary diffractive lens fabricated by EBL, and expect the equivalent effect with the diffractive lens of the saw-like structure.…”