Analysis of extended depth of focus systems with complex pupil decomposition

Abstract

Extended Depth of Focus (EDOF) systems have a broad set of applications in optics including enhancement of microscopy images and the treatment of presbyopia in the aging eye. The goal of EDOF systems is to axially elongate the region of focus for the optical system while simultaneously keeping the transverse dimension of the focus small to ensure resolution. The pinhole effect of reducing the size of the aperture is a well-known means of extending the depth of focus. The pinhole effect however has the drawback of reducing the light entering the system and reducing the resolution of the image. Alternatively, phase masks can be placed in the pupil to enhance depth of focus, maintain light levels and improve resolution relative to the pinhole system. Here, a technique for decomposing these phase masks into a set of quadratic phase factors is explored. Each term in the set acts like a lens and the foci of these lenses add coherently to give the overall focus profile of the system. This technique can give insight into existing EDOF techniques and be used to create novel EDOF phase masks.