Light Sci. Applications 3, e124 (2014)
Planar dielectric structures that can manipulate Bloch surface waves look set to provide new opportunities for constructing flat optical components. Bloch waves are a type of surface electromagnetic wave; like surface plasmon polaritons, Bloch waves are excited by light, but unlike surface plasmon polaritons, they exist in dielectric media instead of thin metal films or nanostructures. Libo Yu and co-workers from EPFL in Switzerland report that by employing multilayer dielectric structures coated with a thin (1/15th of the wavelength) layer of patterned polymer to locally modify the refractive index it is possible to deflect, diffract and focus such Bloch waves. As a first demonstration, the team fabricated a flat plano-convex lens that couples incoming light into Bloch waves, which are then focused. Designs with a greater refractive index contrast and thus different propagation characteristics can be realized by using either thicker polymer layers or alternative materials. The approach could yield a set of two-dimensional, all-optical integrated circuits with applications in sensing, for example. The absence of metal in these designs means that the resulting structures can be low loss, unlike those that employ surface plasmon polaritons.
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