Optical interference filters that have continuously modulated refracti
ve indices throughout their thicknesses (rugates) are designed and fab
ricated using a microwave plasma-assisted chemical vapor deposition te
chnique. Examples are shown of single- and double-response narrow-band
reflection filters made from variable composition silicon oxynitride
deposited on silica. Reflectivities in excess of 99.9% have been reali
zed with bandwidths in the 2 to 10% range.