Interference filter

In telecommunication, an interference filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest.

Note 1: An interference filter may be high-pass, low-pass, bandpass, or band-rejection.

Note 2: An interference filter consists of multiple thin layers of dielectric material having different refractive indices. There also may be metallic layers. Interference filters are wavelength-selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries.

Source: from Federal Standard 1037C