Fabrication and Measurement of Passive Components

Abstract

Since thin films have been used in optics for a considerable length of time, one would expect that the necessary techniques for the production and the evaluation of planar guides were all available when the idea of optical waveguides was first conceived. However, by and large, this was not so. The reason is that, in almost all applications of thin films in classical optics, the films are used at perpendicular or close to perpendicular incidence; the light passes through the film in its shortest dimension, and so, even though in some cases the beam may pass through the film many times, the total optical path in the film is very small. In addition, for most classical applications, such as anti-reflection coatings and multi-layer dielectric mirrors, one does not need to know the mechanical thickness or the refractive index of each layer to a great degree of accuracy. All that is necessary is an accurate knowledge of the optical thickness—a dimension that can be monitored quite easily during deposition—and a nominal value of the refractive index. Indeed, when one peruses the literature on optical thin films, it is remarkable that the index of a film is hardly ever given to an accuracy better than two decimal places.