Experimental demonstration of an approach to designing a metal-dielectric DBR resonant cavity structure

In this paper, we present and experimentally validate a mathematical design methodology for designing DBR resonant cavities with highly complex-index layers at the center. In a conventional DBR resonant cavity, the central layer is designed to be a quarter-wave thick to ensure resonance. Clearly, the concept of a quarter-wave thickness of Au, or any other highly complex film, is not meaningful. However, using the method outlined in this paper, we were able to design, fabricate, and test a SiO₂/TiO₂ DBR resonant cavity with Au as the complex film and demonstrate over a seven-fold enhancement in optical absorption, confirming the validity of this design approach. This methodology is expected to further enable the effective integration of strongly absorbing complex index materials into resonant cavity structures.