2. Realization of Point-of-Darkness and Extreme Phase Singularity in Nanophotonic Cavities

The Aharonov–Bohm effect [1] and the Berry phase [2] are the two important physical phenomena that depends on non-trivial behavior of phase. In particular, singular photonics relies on the abrupt phase changes. The maximum phase change occurs at the point-of-darkness where the incident light is completely absorbed. This phenomenon has been widely investigated using different material systems through the concept of topological darkness [3]. However, to realize topological darkness, sub-wavelength nanostructures are required which demand intense nanofabrication steps. In this chapter, we demonstrate a new approach to realize point-of-darkness and extreme phase singularity using lithography-free metal-dielectric multilayer thin film stacks. We further demonstrate the potential applications of this concept in ultra-sensitive label-free biosensing.