Abstract

Rugate filters are thin films whose refractive index profiles vary continuously in the direction perpendicular to the film plane. Many authors have shown that an approximate relationship between the Fourier transform of the refractive index profile and the reflectance can be used to design these filters. More recently it was established that despite its satisfying efficiency for many cases, this approximation could not provide good designs in all cases.¹ For this purpose a modified Fourier transform was proposed that insured an accurate correspondence between refractive index and reflectance in the case of quarterwave stacks.² This method was based on a distortion of the wavenumber axis that depended on a parameter r which had to be determined empirically. Progress has been made and this paper discusses the choice of this parameter and presents the results obtained for the design of single line rugate filters. Multiline rugate filters are also designed and the influence of incident angle is illustrated for a few particular cases.

© 1989 Optical Society of America