Multilayer dielectric stacks of coupled filters.

The variety of optical filter characteristics obtainable with periodic stacks of two dielectric materials having simply commensurate optical thicknesses can be greatly increased when the basic section consists of more than one pair of layers. Although no more difficult to monitor in coating than stacks of two-layer sections, coupled-filter stacks have stopband spectra which differ considerably from those of their components in much the same way as the transmission characteristics of closely coupled resonators differ from those of their component resonators. The utility of periodic coupled-to-idler frequency ratios not filled by simply periodic multilayers; and two which permit the construction by band-nesting of wide band high-reflectance mirrors for near-ir and visible wavelengths, as well as MacNeille-Banning prisms for the uv region, with lower index ratios than previously envisaged.