The bandpass filter is prepared by depositing multilayer optical materials on the substrate surface. In general, multiple media membrane stacks are separated by a compartment. The dielectric film stack is composed of a large number of dielectric material layers with high refractive index and low refractive index alternately. The thickness of each film in the dielectric film stack is λ/ 4, of which, λ Is the central wavelength of the bandpass filter (that is, the wavelength corresponding to the maximum transmittance of the filter). The spacer layer is located between the dielectric film stacks with a thickness of (n λ)/ 2, where n is an integer. The spacer layer can be colored glass, epoxy resin, dye, metal or dielectric layer. The Fabry-Perot cavity is composed of two dielectric film stacks and a spacer layer in the middle. The filter is installed in a marked metal ring, which can protect the filter and is easy to operate.
