Theory of Induced-Transmission Filters in Terms of the Concept of Equivalent Layers

Abstract

The concept of equivalent layers, previously applied only to all-dielectric multilayer systems, is extended to include symmetrical systems containing absorbing layers. To maximize the potential transmittance of such a system, its parameters must be chosen so that the refractive index of the equivalent layer is real. This choice simultaneously leads to a minimum of the imaginary part of the equivalent phase thickness. The proof involves a novel technique of representing the parameters of the layers by those of a spherical triangle. In the mathematical process, a simple expression is derived for the phase thickness of the dielectric layers of the symmetrical system appropriate to the optimization of its potential transmittance.