There is considerable interest today for filters for fiber optics telecommunications are in the Near Infra-red spectral area. Activity is centered about 1550 nm. Components for Wavelength Division Multiplexer filters used with fiber amplifiers require very high transmission of certain selected wavelengths with very low transmission of an adjacent wavelength in the band of 1530 to 1580 nm. Lasers for this spectral area have a high degree of wavelength variability with operating environments and also with aging. The bandwidth of the filter is specified to pass the signal over a wide range of conditions. Ripple in the passband must also be controlled to meet stringent customer demands. The number of cavities in the filter is determined by the requirements for isolation of allowed wavelengths of the other channel(s).