Cloaking objects, such that their optical response mimics wave propagation in free space, has been a long sought goal since the advent of transformation optics [1]. However, the complexity of the required materials or other... [ view full abstract ]
Cloaking objects, such that their optical response mimics wave propagation in free space, has been a long sought goal since the advent of transformation optics [1]. However, the complexity of the required materials or other inherent problems as the device area severely limit practical realizations. Therefore, many proposed cloaking schemes generally scarify the perfect scattering cancellation [2]. A recent powerful proposal based on the spatial Kramers-Kronig relations, provides a valuable insight to the intimate relation between the material properties and their optical behaviour [3]; still suffering from serious difficulties in terms of practical realizations as it requires infinitely extended permittivity profiles including complex (lossy) materials.
We here propose a different approach following our recently developed general theorem to control the scattering behaviour of an arbitrary object on a specific demand [4], to attain bidirectional optical cloaking for any object with arbitrary shape and size. The design method is based on a generalized Hilbert transform (relating the real and imaginary permittivity) to locally tailor the scattering potential of an arbitrary object as explained in Fig. 1. Furthermore, to extend this idea to cover a specific operational bandwidth rather that a single frequency, as shown in Figs. 1(a), a "half-moon" shaped k-area can be employed to modify the index propel of the initial object, in Fig. 1(b), see Fig. 1(c). We note that the resulting index profile is locally isotropic and we reveal that it is always possible to produce local refractive indices larger than one avoiding the use of gain nor lossy materials. Numerical calculations, using the two-dimensional FDTD method, evidence the bidirectional cloaking with a broad operational bandwidth and wide angular aperture for both directions, working under both polarizations, see Fig.2.
The reported cloaking concept can be easily realized to operate in a wide electromagnetic spectrum from microwaves down to visible wavelengths and to other kind of waves (acoustics), and the operational principle can also be extended to three-dimensional geometries.
[1] Science 312, 1780–1782, 2006.
[2] Phys. Rev.w Appl. 4, 037001, 2015.
[3] Nat. Photonics 9, 1–4, 2015.
[4] arXiv preprint, arXiv:1703.09490 [physics.optics], 2017.
Photonic & plasmonic nanomaterials , Optical properties of nanostructures , Metamaterials
