A Carpet Cloak for Visible Light

Abstract

ABSTRACT:We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nano-porous silicon oxide substrate with a very low refractive index. The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequency. KEYWORDS:Optical metamaterials, invisibility cloak, optical transformation Invisibility cloaks, a family of optical illusion devices that route electromagnetic (EM) waves around an object so that the existence of the object does not perturb light propagation, are still in their infancy. Artificially engineered materials with specific EM properties, known as metamaterials [1,2], have been used to control the propagation of EM waves, and have recently 2 been applied to cloaking through transformation optics [3][4][5][6][7][8]. The invariance of Maxwell's equations under optical coordinate transformation allows the space around the object to be reshaped such that the light can propagate in the desired way. Such transformations usually require EM properties with extreme values that are only achievable in metallic metamaterials, and have been experimentally demonstrated for cloaking in microwave frequencies [9,10]. Due to the significant metallic loss at optical frequencies, the implementation of such cloaks for visible light has been difficult. Recently another innovative strategy was developed based on exploiting uniaxial crystals [11,12]. These devices have demonstrated cloaking in visible frequencies for a certain polarization of light based on intrinsic anisotropy in the crystals. As an alternative, conformal mapping, where an inverse transformation of the electrical permittivity and magnetic permeability leads to a spatially variable refractive index profile [13], can be applied to isotropic dielectric metamaterials. While 3D conformal mapping leads to anisotropic index profiles [14], a 2D quasi conformal mapping (QCM) can be employed to minimize anisotropy. The 2D QCM is the basis for the carpet cloak [15], where the object is hidden under a reflective layer (the carpet). To achieve cloaking, the raised protrusion (the bump) created in the reflective layer is mapped to a flat plane and the resulting 2D index profile forms a carpet cloak device. In contrast to resonant optical structures [16,17], QCM carpet cloak provides a broadband loss-less design and may be invariably extended in the third direction with some limitations [18], experimentally demonstrated to operate for a range of viewing angles [19]. The relatively modest materials requirement from QCM enabled the implementation of the...

Chameleon Devices

“…However, due to the nature of the method, the invisibility effect is only achieved when viewed from direct angles. Cloaking has also been achieved using optical metamaterials (e.g., [12,43]) or light redirection (e.g., [5,18,20,53]. More detail on these types of technology can be found at the end of this paper where we discuss future directions for the research.…”

Invisibility cloaking using pseudomagnetic field for photon

“…As the deepest position corresponds to A x = 2, we can obtain that it is y d = −4.2166b (in virtual space) from the solution in Eq. (9). Finally, the material profile in physical space can be obtained through Eq.…”

“…An invisibility cloak, which hinders the detection of an object by an external observer, is an old fantasy shown in many movies and sci-fi novels but has only recently become practical through the introduction of transformation optics (TO) and metamaterials [1][2][3][4][5][6][7][8][9][10][11][12]. The key feature of an invisibility cloak is that the waves outside the cloak are left undisturbed as if it is just free space, under arbitrary forms of excitations.…”

Diffusive-light invisibility cloak for transient illumination

“…This inspired the creation of new powerful tools such as transformation optics (TO) [2,3], where a space transformation is effectively induced by a suitable medium. As a result, a variety of cloaking mechanisms has been proposed [2][3][4] and even experimentally demonstrated [5,6]. In TO-based invisibility cloaks [2,3], the concealed object is isolated by redirecting the impinging wave around it, preventing any light absorption or scattering.…”