Interferential filter design with continuously variable refractive index

The paper briefly presents an original method for design of inhomogeneous thin films which takes into consideration from the beginning the finite character of the optical thickness. At the beginning, the best solution is obtained in terms of the value of a complex function on a certain spectral grid. At the second step, the design is converted in terms of refractive index profile. Special care is taken to minimize the variations of this profile. Then, a program using this method, written as Windows application, is described together with a design example providing a spectral dependence of the reflectance having the shape of Romanian Athenaeum building.