Abstract
The prospect of rendering objects invisible has intrigued researchers for centuries. Transformation optics based invisibility cloak design is now bringing this goal from science fictions to reality and has already been demonstrated experimentally in microwave and optical frequencies. However, the majority of the invisibility cloaks reported so far have a spatially varying refractive index which requires complicated design processes. Besides, the size of the hidden object is usually small relative to that of the cloak device. Here we report the experimental realization of a homogenous invisibility cloak with a uniform silicon grating structure. The design strategy eliminates the need for spatial variation of the material index, and in terms of size it allows for a very large obstacle/cloak ratio. A broadband invisibility behavior has been verified at near-infrared frequencies, opening up new opportunities for using uniform layered medium to realize invisibility at any frequency ranges, where high-quality dielectrics are available.
Highlights
Transformation optics has been proposed as a general technique to design complex electromagnetic media with exotic properties, opening up paths for effectively rerouting light around an object to be concealed [1,2,3]
Transformation optics based invisibility cloak design is bringing this goal from science fictions to reality and has already been demonstrated experimentally in microwave and optical frequencies
We report the experimental realization of a homogenous invisibility cloak with a uniform silicon grating structure
Summary
Transformation optics has been proposed as a general technique to design complex electromagnetic media with exotic properties, opening up paths for effectively rerouting light around an object to be concealed [1,2,3]. Subsequent experimental realizations of this carpet cloak have been carried out in microwave [6, 7] and optical frequencies [8,9,10,11] in both 2D [6, 8,9,10] and 3D [7, 11] scenarios In those implementations of carpet cloaks, a quasi-conformal mapping technique is taken which neglects the anisotropy of parameters, and structures with spatially varying densities are used to achieve the inhomogeous isotropic parameter profiles. The parameters of the cloak are homogeneous and rigorously designed [18,19,20], not compromising the performance of the cloaking Such a homogeneous cloak has recently been introduced in macroscopic scale based on a natural birefringent crystal and experimentally demonstrated at visible frequencies [21, 22]. By precisely restoring the path of the reflecting wave from the surface, the cloak creates an illusion of a flat plane for a triangular bump on the surface, hiding its presence over a range of optical frequencies (measured between 1480nm to 1580nm)
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