Rugate filter technology is relatively unknown to the Solar PV‐ and the TPV community. The objective of this paper is to draw attention to Rugate filters as an enabling technology that may help to realize unprecedented conversion efficiencies in each respective field. Rugate filters are advanced optical interference filters with a continuously varied refractive index that changes periodically in the direction perpendicular to the film plane. The near noise free transmission and reflection quality of these filters, combined with their precision and the durability, promise significant improvements in the photon economy, performance and reliability of TPV devices. This paper reports the analytical modeling results for a set of Rugate filters designed for the subcells of a novel 4‐bandgap cell system with a new architecture. The purpose of this new approach is to circumvent the limitations of multi‐junction cells to achieve ultimate conversion efficiencies. The purpose of these near‐to‐perfect Rugate filters is to induce spectral splitting of concentrated solar radiation trapped in a Photovoltaic Cavity Converter by selective transmission and reflection of photons. Wideband Rugate filter designs developed for InGaP, GaAs, InGaAsP and InGaAs cells exhibit about 99&percent; average transmission over the spectral response range of the respective cells, while reflecting more than 99 &percent; of the solar photons outside their transmission band. Results of first filter deposition trials are briefly discussed in conjunction with TPV applications. © 2003 American Institute of Physics