ABSTRACT
The main task of any optical designer is to produce an image located in a single plane (the nominal detector plane) by focusing light with the use of optical elements. Unfortunately, images formed at a single image-plane suffer from aberrations due to imperfections in lens action, The deviation from an ideal diffraction-limited image is associated with familiar aberrations, such as thermal and chromatic defocus, coma, and astigmatism, For industrial and military use, imagers are designed to work in hostile environments where the temperature range can be large. This is a particular problem in thermal imaging where the optical components are commonly made with semiconductor materials, such as Germanium, which thave a large temperature coefficient of refractive index, Therefore, an optical system with a large tolerance to defocus aberration will suffer less from chromatic and thermal aberration. The conventional approach to alleviate the defocus aberration is either by introducing additional and complex optical elements, or by including movable corrective mechanisms. Although the original idea of using an hybrid optical/digital system to extend the depth of focus of incoherent imaging systems has been first suggested by Haustler [ 1 ] in 1 972, a significant success has been achieved only recently by Dowski et al [2] , who employed an aspherical phase mask to encode the transmitted wavefront in such a way that the point spread function (PSF) is invariant close to the image plane. In this paper we explore the performance of this modem technique, called Wavefront Coding, with a particular emphasize of the noise amplification associated with application of this technique.
