Optical thin-film filter design with Bragg pair constraint and a divide-and-conquer approach for reduction of the Brewster hole.

Bragg pairs are used as fundamental units to realize optimized thin-film structures. This method is efficient in designing for a large number of layers, such as in a bandpass filter or an edge filter with a relatively wide stopband or angular range. It adapts readily to conventional optimization methodology (such as genetic algorithms). In this paper, the method is first illustrated by application to a conventional high-pass coating on glass, using one set of Bragg pair materials. This demonstrated a 10% improvement over an alternative design technique. A second example is demonstrated using two sets of Bragg pair materials, designed with a more complex merit function, to increase the reflectance around the Brewster angle for p-polarized light. This demonstrated a 19% average reflection improvement across the stopband compared to a two-material design.