Macroscopic Invisibility Cloak for Visible Light

Abstract

Invisibility cloaks, a subject that usually occurs in science fiction and myths, have attracted wide interest recently because of their possible realization. The biggest challenge to true invisibility is known to be the cloaking of a macroscopic object in the broad range of wavelengths visible to the human eye. Here we experimentally solve this problem by incorporating the principle of transformation optics into a conventional optical lens fabrication with low-cost materials and simple manufacturing techniques. A transparent cloak made of two pieces of calcite is created. This cloak is able to conceal a macroscopic object with a maximum height of 2 mm, larger than 3500 free- Significant progress has been made during the exploration of invisibility cloak. The first theoretical model of a transformation-based cloak [3] required extreme values of the constitutive parameters of materials used and can only work within a very narrow frequency band [3,15]. Schurig et al. overcame the first flaw by using simplified constitutive parameters at microwaves based on metamaterial technologies [6]. To bypass the bandwidth limitation and push the working frequencies into the optical spectrum, it has been proposed that an object sitting on a flat ground plane can be made invisible under a fully dielectric gradient-refractive-index "carpet" cloak generated by quasiconformal mapping [5]. This carpet cloak model has led to a lot of subsequent experiments in both microwave [8,13] and infrared frequencies [9][10][11]14]. However, a serious limitation of carpet cloaks was recently pointed out: the quasiconformal mapping strategy will generally lead to a lateral shift of the scattered wave, whose value is comparable to the height of the hidden object, making the object detectable [16]. Furthermore, all previous experiments of invisibility in the optical spectrum, from infrared [9-11, 14] to visible [7,12] frequencies, were demonstrated under a microscope, hiding objects with sizes ranging from the order of 1 wavelength [7,[9][10][11]14] to approximately 100 wavelengths [12]. How to "see" the invisibility effect with the naked eye, i.e. to cloak a macroscopic object in visible light, is still a crucial challenge. In addition, most previous optical cloaks [7,[9][10][11]14] required complicated nano-or microfabrication, where the cloak, the object to be hidden, and the surrounding medium serving as the background were all fabricated in one structure. Thus they could not be easily separated from their embedded structures and transferred elsewhere to cloak other objects. These limitations, such as detectability, inadequate capacity to hide a large object, and nonportability, must be addressed before an optical cloak becomes practical. 2The above limitations boil down to two difficulties in the fabrication of cloak materialsanisotropy and inhomogeneity. The previously proposed quasiconformal mapping strategy attempted to solve anisotropy in order to facilitate metamaterial implementation [5]. However, in conventional optical lens fab...

A Carpet Cloak for Visible Light

“…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.…”

Experimental Measurement Method to Determine the Permittivity of Extra Thin Materials Using Resonant Metamaterials

“…Besides negative refraction property, many other properties of LHMs have now been extensively investigated [8,9]. Currently, many novel applications have been achieved with metamaterials, such as hyperlens [10,11], invisibility cloak [12][13][14][15][16][17], antennas [18][19][20][21] and absorbers [22,23]. In particular, the inclusion of the silk in metamaterials [3] broadens the application of metamaterials.…”

3D Visible‐Light Invisibility Cloak

“…Then, carpet cloaks were introduced; such cloaks are easier to implement because they are based on the principle of hiding an object under a reflective ground plane in a semispace 5. Carpet cloaks have been experimentally demonstrated in the microwave range19, 20, 21, 22, 23 and in the optical spectrum 24, 25, 26, 27, 28. However, carpet cloaks operate by manipulating reflected light to map an object to a “flat” surface instead of making an object “disappear” from transmitted light.…”