These days, if you want to get light… think "Black Hole." The concept of the optical black hole allows us to expect improved performance of photovoltaic cells for generating electricity from the solar radiation.

In many respects, geometric optics has analogies with mechanics, so that the behavior of light in dielectrics resembles that of a physical mass in a potential. In 2009, several research groups suggested the idea of creating an optical analogue of a black hole or, more rigorously, a light attractor. This “black hole” takes the form of a shell of dielectric material, which guides light entering from all directions toward an absorbing core. Apart from being a curious and nontrivial theoretical concept, this idea can potentially be used for improving the performance of solar cells. One of the limiting factors for solar cell efficiency is that not all of the light intensity is absorbed by the active layers, since a significant amount of radiation is scattered. The optical black hole can solve this problem by trapping all light within the required region. The performance of the proposed device is quite impressive: it can absorb almost 100% of the light within a very broad range of frequencies. Even though the idea of an optical black hole seems very attractive, this device is not easy to realize. In particular, the dielectric coating, which is responsible for light trapping, should have a spatially varying index of refraction. At the surface, this index must match that of the surrounding space, and it must grow toward the core. This is where this topic of research becomes intimately related to the field of metamaterials. Metamaterials are man-made structures that allow the engineering of their dielectric and magnetic responses. The design of various artificial spatial distributions of the refractive index in metamaterials has already lead to the creation of invisibility cloaks and lenses with subwavelength resolution.

The numerical calculation of the performance of large-scale optical attractors is a nontrivial problem. In this work, researchers from Queen Mary University of London implemented a parallel finite-difference time-domain numerical algorithm for calculating the wave scattering on the optical black hole. They have confirmed earlier analytical predictions, and they have also studied how the source inside the optical black hole radiates electromagnetic waves. In contrast to a real black hole, this optical analogue does not have an event horizon, and waves can escape from the central region.

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