New manufacturing technologies are reported which produce stabilized optical dichroic filters with spectral immunity to environmental exposures. Optical filters manufactured by this means provide durability and longevity needed for critical fluorometry applications. The trend for environmental monitoring of hazardous petroleum fuels is turning towards optical technologies. State-of-the-art fiber optic chemical sensors based upon fluorescence employ a number of optical components, one of critical importance being a dichroic filter to accurately separate excitation from emission signals. Optical interference filter production consists of the physical vapor deposition of multilayer thin films upon suitable substrates. Conventional electron-beam thin-film evaporation techniques yield films having porous structures; the resultant filters are spectrally unstable when exposed to varying environmental conditions. The use of this type of filter in fluorescence instrumentation can result in unacceptable drift and therefore significant inaccuracies in vapor detection. The new Corion Reactive Low Voltage Ion Plating Process (RLVIP) produces durable stabilized filters having fixed, permanent characteristics immune to harsh environmental exposures. This novel manufacturing process is described, and the durability, stability and longevity of these filters are evaluated. Spectral measurements, as well as environmental exposure test results are presented. Important applications of these new products are reviewed. Comparisons with traditionally manufactured filters are made.