Abstract

The use of very thin layers in the design of advanced thin-film devices has been proposed as a method of generating arbitrary index profiles.¹ Thin layer pairs deposited sequentially and in the correct ratio of thicknesses have been shown to exhibit, as far as the incident light is concerned, an effective index that lies between the index values of the constituent materials. However, the deposition of these layers presents a considerable challenge to the coating engineer since the thicknesses of these layers are much less than the wavelength of light. In addition, some designs may require a thickness tolerance of 1 % or less. These requirements cannot be met using standard optical or crystal thin-film monitors. This paper describes a system used for the fabrication of filters that incorporate such layers. Ellipsometric monitoring techniques are discussed that allow the accurate measurement of very thin optical films. The results of several advanced filter designs are presented.

© 1986 Optical Society of America