Starting from the theory of one-dimensional photonic crystal, a flat-top polarization interleaver filter composed of cascaded thin-film glass cavities is proposed. A detailed design example with three cascaded thin-film glass cavities is given in the paper. The minimum transmissivity of P polarized light at passband is higher than 99.6% and the maximum transmissivity of S polarized light is about 0.1%. The center-frequencies of the transmissivity of P polarized light accord with the ITU standard. The proposed interleaver filter not only has the characteristics of very simple structure, easy to accomplish, but also has high transmittance for P polarized light and good cut-off characteristic for S polarized light. When rotating the cascaded thin-film glass cavities in the horizontal plane with small angle, the filter has the center-frequency tunability characteristic as well.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.