Macroscopic Invisibility Cloak Hides Objects in Visible Light

An invisibility cloak hides objects in visible light - SmartPlanet

For the first time, physicists from two separate groups have created rugs that can hide objects in visible light. The scientists made carpet cloaks from calcite crystals. The calcite crystal cloaks are more affordable than traditional cloaks. Calcite crystal is naturally occurring and is a cheap optical material.

Baile Zhang, an engineer at the Singapore-MIT Alliance for Research and Technology Centre, created a cloaking rug that can hide objects that can be seen by the naked eye. The object looks hidden because light reflects off the surface. The carpet-cloaking device can hide things in the millimeter range and do so in visible light.

But don’t get too excited, the cloak isn’t perfect. It only works if you’re looking at it at the right angle.

The cloak was designed to work under water.

Macroscopic Invisible Cloak for Visible Light

[...]  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-space-wavelength, inside a transparent liquid environment. Its working bandwidth encompassing red, green and blue light is also demonstrated.


A light ray is incident on a flat ground plane and reflected back with the same angle.
(b) When an object is sitting on the ground plane, the reflected ray changes its angle. (c) When another flat ground plane is put on top of the object, the reflected ray restores its angle but suffers a lateral shift. (d) When a transformation-based anisotropic cloak is covering the object, the reflected ray restores both its angle and position. The anisotropic medium has two principal refractive indexes n1 and n2 along two orthogonal directions. The observer in all cases is assumed to have a fixed height of h. In (b) and (c), the original position of the observer is indicated with a dotted eye.

A transformation-based anisotropic cloak compared to a steel wedge on top of a mirror.
The cloak is made of two pieces of calcite crystal with specific orientations of the optical axis indicated by the yellow dotted arrows. For green light, with its magnetic field perpendicular to the optical axis, n1 = 1.48 perpendicular to the optical axis and n2 = 1.66 along the optical axis [...]

Invisibility rug hides 'large' objects : Nature News

By contrast, an independent group led by physicists Shuang Zhang at the University of Birmingham, UK, and John Pendry from Imperial College London has built a calcite cloak that can work in air, hiding objects a few centimetres high.

Macroscopic Invisibility Cloaking of Visible Light

[...] Here we report realisation of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices.


Dr Shuang Zhang discusses his work into Metamaterials within The School of Physics at The University of Birmingham.