Reflection filter multilayers of metallic and dielectric thin films

Narrowband spectral filters operating in reflection and consisting of multilayers containing both dielectric and metallic films are of interest for fiber-optical communication systems at wavelengths from 1250 to 1600 nm. Formulas are derived which relate the potential transmittances of the main metallic film to important specifications of the filter, namely, bandwidth and rejection, and it is shown how the parameters of the layers are chosen to meet these and other requirements such as free spectral range. Monitoring procedures are discussed, and the results of photometric observations on five filters are compared to theoretical predictions.