Design and experimental approach of optical reflection filters with gradedrefractive index profiles

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