Anderson Localization of Visible Light on a Nanophotonic Chip

Abstract

Technological advances allow the control of light at the nanoscale and to strongly enhance the light–matter interaction in highly engineered devices. Enhancing the light–matter interaction is needed for applications in research areas such as quantum technology, energy harvesting, sensing, and biophotonics. Here, we show that a different approach, based on the use of disorder, rather than the precise engineering of the devices, and fabrication imperfections as a resource, can allow the efficient trapping of visible light on a chip. We demonstrate, for the first time to our knowledge, Anderson localization of light at visible wavelengths in a nanophotonic chip. Remarkably, we prove that disorder-induced localization is more efficient in confining visible light than highly engineered optical cavities, thus reversing the trend observed so far. We measure light-confinement quality factors approaching 10 000 that are significantly higher than values previously reported in two-dimensional photonic crystal cavities. These measurements are well explained using a three-dimensional Bloch mode expansion technique, where we also extract the mode quality factors and effective mode volume distributions of the localized modes. Furthermore, by implementing a sensitive imaging technique, we directly visualize the localized modes and measure their spatial extension. Even though the position where the cavities appear is not controlled, given the multiple scattering process at the basis of their formation, we are able to locate with nanometer-scale accuracy the position of the optical cavities. This is important for the deterministic coupling of emitters to the disorder-induced optical cavities and for assessing light localization. Our results show the potential of disorder as a novel resource for the efficient confinement of light and for the enhancement of the light–matter interaction in the visible range of wavelengths.