Applications of reverse engineering in the fabrication of optical coatings with high performance

Abstract

Reverse Engineering attempts to derive information about the makeup of an existing optical coating from optical spectrum measurements, usually of performance, which can be converted into targets for inverse optimization synthesis. In the method of inverse synthesis, optimization targets are measured spectral data, the starting design is the original theoretical design and the final results gives more actual indices, layer thickness, dispersive index functions and material tooling factors, or some of them by selected optimization for multi-layers. This paper presents some new optimization methods, such as gradually constrained optimization approach, subsection synthesis, accelerating optimization model, etc. The methods applies to all kinds of transmission spectra and do not rely on the existence of interference fringe patterns or transparency. Through a lot of experiments of the films Ta 2 O 5 , TiO 2 under different ion-assisted deposition (IAD) conditions, the deviation between the measured and the theoretical spectra data is less than 0.52% in p-order model merit function, which shows that these methods are reliable. With Reverse Engineering for multi-layers, we have successfully manufactured 400-700nm broadband antireflection coatings (average reflectivity is around 0.25%, maximum reflectivity is on more than 0.35%) and broadband beam splitters (R/T=30:70 for a 45 degree angle of incidence, average reflectivity deviation is less than 2.5% in visible spectral region). Of course, many difficulties have not still been overcome, especially for multi-layers.