Optical metamaterials and their unusual properties
Artificially engineered metamaterials have emerged with properties not available in natural materials. The intricate behaviour of this new class of electromagnetic materials is interesting from both a fundamental and a practical view. Metamaterials have already been developed with linear responses that could be used to improve sensors and even permit invisibility by cloaking. In the same way, research work on the revolutionary physics of non-linear metamaterials could revolutionise the non-linear optics field. Within the EU-funded project META-PHOT (Light-matter interaction in smart optical materials), researchers investigated the origin and design of non-linearities with a focus on their application in optical devices. The META-PHOT team designed new optical effects as a result of light interaction with an ultrathin film of artificially structured material on top of a conventional material layer. Importantly, they demonstrated a new concept of local phase manipulation when light passes through this metasurface that is based on plasmonic nanostructures. Nanometre-sized plasmonic antennas were arranged to generate a special polarisation state of light, circular polarisation. Based on this nano-antenna design, the focal length of an ultrathin lens depended on the polarisation state making the optical system easily reconfigurable. In their experiments, the researchers used an ultrathin layer of well-defined plasmonic antennas with a thickness only a fraction of the used light wavelength. A tuneable laser system provided the required wavelength to evaluate its performance and obtain proof of selection rules for non-linear processes in natural materials. In addition to the ultrathin lens, the new plasmon coupler of surface electromagnetic waves was developed that has the potential to excite directional waves along the metasurface. However, beyond the possibility of enhanced light-matter interaction, there are many other intriguing non-linear optical processes in metasurfaces awaiting exploration. META-PHOT highlighted the potential of tailoring non-linear processes in designing completely new optical elements for nano-optical devices, bound to broaden the horizon for their applications.
Keywords
Optical metamaterials, non-linear optics, META-PHOT, light-matter interaction, nano-optical devices
