Synopsis: Isotropy can’t be swept under a carpet cloak

The caveat that a carpet cloak must be made of an anisotropic material should not be ignored.
Synopsis figure
Illustration: B. Zhang et al., Phys. Rev. Lett. (2010)

Invisibility cloaks—optical materials that hide objects by distorting the path of light or altering its scattering pattern—have captured the imagination of scientists and the public alike. Unfortunately, an obstacle to manufacturing cloaks is the need to make them from anisotropic materials, which are difficult to engineer at optical frequencies.

In 2008, Li and Pendry [1] proposed the idea of a “carpet cloak,” whereby the hidden object lies under a smooth bump that appears flat to the observer. In principle, the carpet cloak must also be made of an anisotropic material, but Li and Pendry showed that even side-stepping this requirement, one can obtain cloaking, albeit as an approximation to the exact problem.

But could the isotropic approximation introduce image distortions large enough to give away the cloaking effect? Writing in Physical Review Letters, Baile Zhang, Tucker Chan, and Bae-Ian Wu at the Massachusetts Institute of Technology in the US trace a light ray reflected from an isotropic carpet cloak. They find an isotropic cloak preserves the phase but not the direction of the scattered light. Instead, the ray is shifted laterally—in some cases by an amount comparable to the object itself—leaving a telltale signal that what appears as empty space may be the presence of an object.

Zhang et al.’s efforts to outline the fundamental and practical limitations of using isotropic media instead of anisotropic ones should inform the search for broadband, optical cloaks, as well as a wide range of devices and applications in transformation optics. – Manolis Antonoyiannakis

[1] J. Li and J. B. Pendry, Phys. Rev. Lett. 101, 203901 (2008).


More Features »


More Announcements »

Subject Areas


Next Synopsis

Atomic and Molecular Physics

Raman thermometer for fermions

Read More »

Related Articles

Focus: 3D Images 10 Times Faster
Interdisciplinary Physics

Focus: 3D Images 10 Times Faster

3D x-ray phase-contrast images take as little as one-tenth the usual time to acquire using a technique that halves the number of required “photos.” Read More »

Viewpoint: Photonic Hat Trick

Viewpoint: Photonic Hat Trick

Two independent groups have provided the first experimental demonstration of genuine three-photon interference. Read More »

Focus: <i>Image</i>—Sound Waves Guided Along Curvy Path
Condensed Matter Physics

Focus: Image—Sound Waves Guided Along Curvy Path

A new image from 3D computer simulations demonstrates that tiny, randomly arranged pillars can allow an acoustic wave to be efficiently guided through an arbitrarily shaped channel. Read More »

More Articles