24 - GRIN optics: Practical elements

Abstract

This chapter describes the practical elements of GRIN optics. An inhomogeneous medium is one in which the refractive index profile varies from point to point within the medium. Currently, the terms “Gradient Index” or “Graded Index” (GRIN) are often used to describe such a medium. There are three basic gradient index types: axial, radial, and spherical. Axial gradient has an index of refraction that varies only in a continuous way along the optical axis. Radial gradient has an index of refraction that varies only as a function of the distance r from the optical axis. Spherical gradient may be thought of as a symmetric index around a point whose iso-indicial surfaces are concentric spheres. In a GRIN medium, the optical rays follow curved trajectories, instead of straight lines as in a homogeneous medium. By an appropriate choice of refractive index profile, a GRIN medium can have the same effect on light rays as a conventional optical component, such as a prism or a lens. Various methods of producing GRIN materials have been developed but these processes are limited by the small variation of the index, the small depth of the gradient region, the minimal control over the shape of the resultant index profile, and the cost. Finally, light propagation in cylindrical or planar GRIN media with a wide variety of gradient profiles has been analysed with emphasis on the wave guiding properties of importance for optical communications and optical sensing.