Optical characterization of SiO2-TiO2 thin films with graded refractive index profiles

Development of high-quality optical filters has received considerable atten tion because it's important device in the wavelength division multiplexing technique to realize optical communication with high speed and great capaci ty. In this work, the graded refractive index profiles are induced in the s tructure of designed multilayer filters by means of the concept of the func tionally graded materials (FGM). Optical characterization of designed and f abricated novel filters with graded refractive index profiles in the SiO2-T iO2 system was investigated. Designed reflection filters have the symmetrical structure with graded refr active index profiles combining with the layers modifying index difference and exhibit higher optical performance than unmodified rugate filter. Desig ned transmission filters exhibit almost 100% transmittance at the designate d wavelength band which can be changed in the range from 1 to 50 nm and a w ide reflection region with almost 100% reflectance. A designed 31-layer SiO 2-TiO2 film with graded refractive index profiles was fabricated by helicon plasma sputtering and which has superior process controls and consequently better reproducibility. The measured transmittance spectrum exhibited a re flectance of 99.8% at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band, which correspond ed well with calculated one.