Abstract
Wave propagation in disordered media can be strongly modified by multiple scattering and wave interference. Ultimately, the so-called Anderson-localized regime is reached when the waves become strongly confined in space. So far, Anderson localization of light has been probed in transmission experiments by measuring the intensity of an external light source after propagation through a disordered medium. However, discriminating between Anderson localization and losses in these experiments remains a major challenge. In this paper, we present an alternative approach where we use quantum emitters embedded in disordered photonic crystal waveguides as light sources. Anderson-localized modes are efficiently excited and the analysis of the photoluminescence spectra allows us to explore their statistical properties, for example the localization length and average loss length. With increasing the amount of disorder induced in the photonic crystal, we observe a pronounced increase in the localization length that is attributed to changes in the local density of states, a behavior that is in stark contrast to entirely random systems. The analysis may pave the way for accurate models and the control of Anderson localization in disordered photonic crystals.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Enhancing the interaction between light and matter is the essence of many research disciplines, including quantum information science, energy harvesting and optical biosensing. The traditional method has been to strongly confine light in, for example, a highly ordered nanocavity. Surprisingly, an alternative approach to confinement of waves exists, originally proposed by Philip Anderson, and for which he was awarded the Nobel Prize for physics. Using this approach, disordered materials are employed, giving rise to random and multiple scattering of the propagating light waves. For a certain amount of randomness of the structures, so-called Anderson localized modes form spontaneously: light is trapped in a maze.
Main results. A challenge in this research field has been to determine how well light can be confined based on random disorder. We have developed an efficient method for exciting Anderson-localized modes by embedding nanoscopic light sources (so-called quantum dots) inside the disordered material. By analyzing the statistics of the emitted light, the quality and extent of light confinement can be extracted.
Wider implications. Surprisingly, the subtle interplay between the amount of disorder and the underlying periodic structure of the system studied can be exploited to confine light very efficiently, proving the potential of employing disorder for enchancement of light–matter interaction.
Figure. When a photon wave packet propagates through a randomly structured medium it is repeatedly scattered at the obstacles. Such a multiple scattering process leads to wave interference, which can prevent the photon from escaping the medium: the photon is trapped in a maze. This intriguing phenomenon is called Anderson localization and can be exploited to efficiently enhance the interaction between light and matter and is of potential use for quantum information technology.