Introduction to Theory of  Gradient-Index Elements

doi:10.1117/3.2570044.ch2

Introduction to Theory of Gradient-Index Elements

Book: Optics of Diffractive and Gradient-Index Elements and Systems

Author(s): Grigoriy I. Greisukh, Sergei T. Bobrov, Sergei A. Stepanov

Published: 1997

https://doi.org/10.1117/3.2570044.ch2

Author Affiliations +

Abstract

In the previous chapter we considered the main features of the wave front transformation by infinitely thin optical elements. When a wave is incident upon such an element, the wave-front and direction of propagation, in general, undergo an abrupt change. Deflecting properties of prisms and diffractive gratings, as well as focusing properties of diffractive and homogeneous lenses, are based on the transformation of a wave-front by infinitely thin optical elements. If a wave propagates in an inhomogeneous medium, then, due to the change of the phase velocity, a continuous transformation of the wave-front occurs and the corresponding rays bend smoothly towards the refractive index gradient. If all the rays of a light beam bend in the same fashion, such an inhomogeneous medium is like a prism. If off-axis rays of the beam bend more than near-axis ones, such a medium has certain focusing properties. As a result, a slice of inhomogeneous material can be like a conventional prism or lens or combine the properties of both elements or even play a more sophisticated role. A lens with spherical surfaces can be made from an inhomogeneous material. In this case, because there are more degrees of freedom, new good possibilities of correcting aberrations arise. All this certainly deserves serious interest when optical systems are designed because it simplifies the design and improves the quality of the system. However, to be able to do it, one should thoroughly understand how optical elements made of inhomogeneous materials act and how the light propagates in these materials. This chapter considers these problems.