This paper gives a brief review of the principal literature data on optical graded-index elements made from glass. It describes the results of work at the State Optical Institute on the development of the compositions and the study of the properties of the starting glasses, on the kinetic and thermodynamic parameters of the ion-exchange processes between the starting glasses in the softening-temperature interval and melts of a mixture of salts, and also on the study of mass transfer between melted glasses. The processes by which the refractive-index profile is formed in the resulting graded-index elements are characterized. The results of a theoretical treatment of the improvement of the parameters of graded-index elements by using the metric of the equilibrium chemical diagram are briefly explained.
A. K. Yakhkind, "Optical graded-index elements made from glass," J. Opt. Technol. 70, 877-881 (2003)