Effect of stress on performance of dense wavelength division multiplexing filters: thermal properties

Thin-film filters used for dense wavelength division multiplexing (DWDM) applications are processed by a variety of deposition techniques, including ion-beam sputtering. Ion-beam sputtering produces high-quality coatings and provides flexibility of coating materials. However, DWDM filters consisting of oxide films that are reactively deposited by ion-beam sputtering, as in most sputter techniques, typically exhibit high levels of compressive stress. This affects the thermal characteristics of the filters. We have identified three thermal effects: center wavelength drift with temperature, center wavelength creep, and permanent center wavelength shift. The latter two are strongly dependent on the stress state of the filter. Models are presented that support the data that were taken.