Manufacture of complex optical multilayer filters using an automated deposition system

Abstract

It is now possible to design complex thin film multilayer coatings that can achieve almost any desired spectral performance. Moreover, these coatings can consist of tens or hundreds of layers each of which may have a different thickness. It is a challenge to accurately manufacture such complex coatings. An automated deposition system (ADS) has been developed which is able to fabricate complex optical coatings on a routine basis. This deposition system uses a wideband optical monitor to accurately determine the deposited layer thickness and to re-optimize the remaining layer thicknesses, if required. One advantage of this process is that no operators are required during the manufacture of a filter. For this technique to work, however, an energetic deposition process such as sputtering is necessary in order to achieve thin films with a bulk-like refractive index with little or no porosity or inhomogeneity. As well, the optical constants of the thin film materials must be accurately known. A number of thin film filters have been manufactured using this ADS. These include all-dielectric coatings as well as metal/dielectric filters. In this paper, the ADS and the real-time process control algorithms will be described in more detail and several examples of manufactured complex thin film filters will be described for different applications.