Plasmonic metamaterials

Transformation optics

This new method uses differential-geometric techniques to find out the properties that a medium should have in order to curve or distort electromagnetic space in almost any desired way. It has made it possible to build devices such as invisibility cloaks or optical black holes. Our work includes the development and application of design methodologies that simplify the optical properties required to synthesize transformation-optics-based devices (e.g. quasi-conformal mappings). Moreover, we have designed devices with unusual properties such as flat reflectionless squeezers and hyperlenses, special radiation-pattern-shaping devices, and light-surface plasmon polariton couplers with increased angular bandwidths. In addition, we are working on the extension of the full possibilities brought about by transformation optics to other fields of physics.

Results

Full 3D isotropic transformation media

Although transformational techniques reach their full potential and flexibility in 3D, the implementation of 3D transformations is frequently out of the reach of current technology due to their general anisotropic character. In a recent paper [1], we show how the use of a special kind of shape-preserving mappings and a subsequent optimization algorithm allows one to completely remove this anisotropy. The method is general and can be applied to any field for which a transformational technique exists, such as optics, acoustics, or thermodynamics.

Figure result

References

[1] "Full three-dimensional isotropic transformation media", C. García-Meca; R. Ortuño; J. Martí; A. Martínez, NEW JOURNAL OF PHYSICS, Vol. 16, pp. 023030, February 2014.

Analogue transformations

Using the idea of analogue spacetimes, we have developed a generalization of transformation optics that can be applied to fields described by non-form-invariant equations [1]. The method is general and could be considered as a new paradigm for controlling waves in different branches of physics, from acoustics in quantum fluids to graphene electronics. As an application, we derive an "analogue transformation acoustics" formalism that naturally allows the use of transformations mixing space and time or involving moving fluids, both of which were impossible with the standard approach. To demonstrate the power of our method, we have designed different novel acoustic devices such as a dynamic compressor or a spacetime cloak.

Figure result

References

[1] "Analogue Transformations in Physics and their Application to Acoustics", C. García-Meca, S. Carloni, C. Barceló, G. Jannes, J. Sánchez-Dehesa, and A. Martínez, NATURE SCIENTIFIC REPORTS, 3, 2009, June 2013.

Broad angle coupling of free-space light to surface plasmons with a flat slab

Researchers at NTC demonstrate theoretically that free-space light can be coupled to surface plasmons by means of a flat squeezing slab designed with transformation optics. Unlike prism couplers, the proposed device does not introduce reflections at its input interface. Moreover, the angular response of the device can be engineered by using a non-uniform compression factor. As an example, a particular configuration of the device with a half-power angular bandwidth 2.5 times higher than that of a conventional dielectric coupler was designed.

Figure result

References

[1] "Exciting Surface Plasmons with Transformation Media", C. García-Meca; R. Ortuño; J. Martí; A. Martínez, PLASMONICS, Vol. 7, n. 4, pp. 701-707, December 2012.

Broadband radiation pattern engineering with isotropic materials

Researchers at NTC have developed a method that allows for engineering optical devices that modify the radiation pattern of a point source in a highly flexible way. A wide variety of complex radiation patterns can be achieved, which can combine high directivity in a desired number of arbitrary directions and isotropic radiation in other specified angular ranges. In addition, the proposed devices are broadband and only require an isotropic refractive index for their implementation.

Figure result

References

[1] "Engineering antenna radiation patterns via quasi-conformal mappings", C. García-Meca; A. Martínez; U. Leonhardt, OPTICS EXPRESS, Vol. 19, n. 24, pp. 23743-23750, November 2011.

Squeezing light without reflections

Researchers at NTC have found a way to compress free-space light and transfer it to a simple medium without reflections. The studied squeezers can be designed to act as ultra-short perfect coupler for high-index nanophotonic waveguides or completely flat reflectionless hyperlenses. The properties of this kind of devices can be engineer so as to require only non-magnetic isotropic materials for their implementation.

Figure result

References

[1] "Squeezing and expanding light without reflections via transformation optics", C. García-Meca; M. M. Tung; J. V. Galán; R. Ortuño; F. J. Rodríguez-Fortuño; J. Martí; A. Martínez, OPTICS EXPRESS, Vol. 19, pp. 3562-3575, 2011.