Understanding the diffractive bifocal contact lens.
How a diffractive bifocal contact lens works is not intuitively obvious. This is because the diffractive bifocal operates by an unusual blend of refraction and interference. The present article seeks to clarify how it achieves its two focal powers. Most of this article, however, is devoted to the conceptually simpler case of diffraction gratings in order to develop an intuition for how a double focus is produced. Single slit, double slit, and multiple slit gratings are considered using two formalisms: Feynman's "arrow" method (also called phasors) and the Fourier method. When dealing with linear diffraction gratings we are interested in the light intensity in the focal plane. By a simple redefinition of variables, all of the mathematics for diffraction gratings can be applied to circular lenses. For this latter case instead of looking at the light intensity in the focal plane, we look at light intensity on the optic axis. The appearance of two focal points is a simple consequence of a combined interference and diffraction pattern. The goal of this article is to present an introduction to Fourier optics and an analysis of the bifocal contact lens in a reader-friendly manner.
Phase function design of a diffraction grating lens for an optical imaging system from a Fraunhofer diffraction perspective.
The potential exists to apply diffraction gratings to optical imaging systems to improve camera resolution and shorten optical length. However, we have noted the generation of striped flare lights, which differ from unnecessary-order diffraction lights, under intense lighting. We have elucidated the generation principle of these new striped lights and have discovered that they are caused by narrow diffraction grating rings. In this paper, using an analysis based on Fraunhofer diffraction, we suggest a way of minimizing them by designing an appropriate phase function structure, and test the efficacy of this design using our own manufactured prototype.
Retinal image quality with different designs of bifocal contact lens
Abstract The design of alternating andsimultaneous-vision bifocal contact lenses is discussed in relation to the form of the geometrical point images (spot diagrams) that they produce on the retina. Examples are given to show that the effects of variations in lens decentration and in the diameter of the entrance pupil of the eye depend upon the lens design used. An alternative interpretation of imaging performance in terms of the through focus modulation transfer function is briefly outlined.