Design and experimental approach of optical reflection filters with graded refractive index profiles

A novel optical multilayer filter with graded refractive index profiles using a quarterwave stack was designed. This filter exhibits a high reflectance band, a sharp cutoff and a wide transmittance region as the result of sidelobe suppression. A 31 layer TiO2/SiO2 high reflectance filter with a graded refractive index profile was fabricated by helicon plasma sputtering on BK7 and Si (100) substrates. The deposition system was operated under ambient gas pressure of 1.8 x 10(-1) Pa at room temperature. The measured transmittance of the spectrum was in good accord with calculated results, Transmission electron microscopic observations confirmed the expected microstructure of the filter. (C) 1999 American Vacuum Society. [S0734-2101(99)03201-3].