A 2016 paper in Optics Express, “Advanced optical interference filters based on metal and dielectric layers”, reports fabricating an optical filter with 105 nano-scale thin film layers to tailor the transmission and reflection spectra to the specifications of a manufacturing problem contest. Here are the measured curves of the resulting filter in blue, compared to the challenge problem in red.
The paper concludes:
A complete description of the design and the fabrication procedures of an advanced optical interference filter based on metal and dielectric layers was presented. We first analyzed the difficulties in designing such a component using conventional design tools due to the presence of absorption and showed that using the combination of global optimization procedure with needle technique, it is possible to obtain a promising, but complex and error-sensitive, design composed with 105 layers and a single metallic layer. We then fabricated such a filter using plasma-assisted reactive magnetron sputtering. Using virtual deposition process, we first validated the monitoring procedure. It is based on the decomposition of the design into three different parts, i.e. the dielectric layers between the substrate and the metallic layer, the metallic layer, and the remaining dielectric layers. Optical monitoring of the dielectric layers was carried out using respectively 5 and 3 different test glasses for the first part and the third part of the design. We also developed a specific procedure to account for the specific properties of the metallic layer. Using the combination of all these strategies, we managed to demonstrate an optical filter with complex shape and a good merit function within 2.5.