Thin-film thickness-modulated designs for optical minus filter.

We proposed an analytical method to design optical minus filters by the thickness modulation of discrete, homogeneous thin-film layers of a two-material multilayer coating. The main stack provides the narrow, second-order rejection band, and the correct thickness-modulation apodization and match layers can effectively suppress the sidelobes of the passband. Using this approach, we can design minus filters with layer thicknesses close to half-wave of the rejection wavelength, making this method well suited for accurate monitoring during the deposition.