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Proceedings Paper

Achromatization of the diffraction efficiency of diffractive optical elements
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Paper Abstract

Diffractive optical elements (DOEs) are characterized by a large negative dispersion. This property can be exploited to correct chromatic aberration in hybrid optical systems. The diffraction efficiency of phase DOEs decreases when the wavelength deviates from the design wavelength. Consequently, DOEs are usually applied only in optical systems where the spectral bandwidth is limited. Thus the dilemma that the chromatic correction capability of the DOE can not be fully exploited in optical systems with large spectral bandwidths where the correction could be most useful. It has been shown that by careful selection of the dispersion properties of two different optical materials it is possible to achromatize the diffraction efficiency of the DOE in a sandwich configuration, Fig. la.1 The dispersion properties of the two materials must be matched such that refractive index change at the interface, An(2), remains proportional to the wavelength, A, i.e.AIzn() = constant. The introduction of a second surface profile removes the above constraint on the dispersion properties of the materials. Such an approach has been described where an air gap has been inserted between the two materials and the depth of the surface profile for each material are optimized to minimize the variation of the phase modulation with wavelength, Fig. lb.2 Better performance can be achieved by placing the second surface relief on the exterior of one of the sandwiched materials, Fig. ic. The advantages are reduced shadowing effect, less Fresnel reflection losses, and much better fabrication tolerances. Furthermore, the second surface profile has removed the materials limitation. Materials that are much better suited to fabrication can be used, thus allowing for mass fabrication at reduced costs.

Paper Details

Date Published: 19 July 1999
PDF: 2 pages
Proc. SPIE 3749, 18th Congress of the International Commission for Optics, (19 July 1999); doi: 10.1117/12.354794
Show Author Affiliations
Kenneth J. Weible, Weible OpTech (Switzerland)
Andreas Schilling, Univ. of Neuchatel (Switzerland)
Hans Peter Herzig, Univ. of Neuchatel (Switzerland)
Daniel R. Lobb, SIRA Ltd. (United Kingdom)

Published in SPIE Proceedings Vol. 3749:
18th Congress of the International Commission for Optics
Alexander J. Glass; Joseph W. Goodman; Milton Chang; Arthur H. Guenther; Toshimitsu Asakura, Editor(s)

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