Abstract

The potential of Fresnel lenses as imaging elements at IR frequencies has been studied. The advantages offered by Fresnel lens elements are particularly attractive in IR systems where weight, cost, and compactness are often at a premium. Moreover, single-point diamond turning technology has made it possible to produce sophisticated Fresnel lenses with surfaces of good optical quality. In general, for example, facets of an aspheric profile can be formed on both surfaces of a meniscus substrate. Molding from diamond machined dies introduces the possibility of cheap mass-produced plastic elements; the inherently thin construction helps to compensate for the poor transmissive characteristics of these materials at IR frequencies. The performance of these complex Fresnel lenses in image forming systems is discussed in terms of the point spread and modulation transfer functions. The aberration-free case is examined and used to define an optimum structure in terms of the number of facets and their dimensions. The effect of aberrations on the imaging characteristics is discussed, and a tolerance for these defects is suggested. Some theoretical results are presented for a set of practical designs together with measurements from a diamond turned germanium Fresnel lens.

© 1988 Optical Society of America