Commentary: Quantum way for metamaterials
Résumé
The field of nanophotonics witnesses a sort of golden age, where many new fields, such as plasmonics, metamaterials, transformation optics, have risen recently, leading to a wealth of new directions of research. The story started more than 20 years ago, when new artificial structures were imagined that could exhibit a photonic bandgap. These structures were called photonic crystals.1 They have carried a lot of hope on the possibility of molding the flow of light. It was indeed soon recognized that they could go way beyond the bandgap and that, in fact, they had a very rich band structure that allowed for control over the propagation of light itself, inside the photonic crystal. This has led to such effects as ultrarefraction, slow light, control of second harmonic emission, gradient photonic crystals, and negative refraction. Somehow, this wealth of properties has slowed down researches with the original quantum flavor of photonic crystals, at least as it appeared in the work of Sajeev John, which were seen really as devices able to control the Purcell effect. This was, for instance the case for the idea of realizing a laser cavity with a very low threshold. This aspect has shown a renewed interest recently.2