Optical filters from SiO2 and TiO2 multi-layers using sol–gel spin coating method

Sol–gel spin coating process is used to produce optical filters from SiO2 and TiO2 multi-layers. By coating the films symmetrically on both sides of the glass substrates, we designed two types of three-layer anti-reflective (AR) filters for the near–infrared region, and a nine-layer reflective filter for the near–UV region. We develop a simple theoretical model for these filters, which incorporates sol–gel film densification during the coating process, and fit it to the experimental data to extract properties of the individual layers in the coatings.