Narrow-band interference filters with unconventional spacer layers

Classical narrow-band interference dielectric filters with all-dielectric reflectors have quarter-wave stacks separated by a half-wave thickness (or a multiple-) spacer layer. These filters are essentially Fabry-Perot filters; hence the theory developed for those filters applies in full. The theory of narrow-band interference dielectric filters with unconventional spacer layers is presented. This spacer layer consists of two different materials. The optical features of these filters are compared with the features of Fabry-Perot filters. The influence of the errors of the layers on spectral characteristics is analyzed. The theory presented can be applied to any spectral range as well as to any thin-film material, including absorbing and nonlinear materials.