Skip to Content
Uncategorized

More Large-Scale Invisibility Cloaks, This Time From China and Beyond

Big, cheap invisibility cloaks are suddenly beginning to emerge thanks to some simple optical short cuts that physicists have discovered

Last week, we looked at an invisibility cloak large enough to hide a human and that works across all optical frequencies. This cloak was simple in design, cheap to build and, perhaps most important of all, scalable to almost any size.

It had one serious drawback, however. This cloak only worked when viewed from one direction. Look at this device from any other angle and its cloaking effect is lost.

Today, Hongsheng Chen at Zhejiang University in China and an international circle of friends, reveal a different take on the same design. These guys have created large-scale invisibility cloaks that work over the entire optical spectrum but can cloak in several directions at once.

Invisibility cloaks work by steering light around a cavity to make it look as though it wasn’t there. This is a difficult job to do perfectly since any light rays that are steered around an object must travel faster than neighbouring rays that do not change direction. That requires various superluminal tricks that are difficult to master.

But Hongsheng and co point out that this need to keep up with the neighbours is only necessary when the objects are viewed with coherent light in which the waves are in phase. That’s not the case for human vision in the optical spectrum, which is broadband and incoherent. Humans, and indeed most other creatures, are not sensitive to the phase of light or changes in polarisation.

Hongsheng and co point out that relaxing this requirement suddenly makes invisibility cloaks much easier to design and build on a large scale. “Therefore, abandoning the requirement of phase preservation for natural light cloaking opens the door to hide large-scale living creatures,” they say.

Like the cloaks we looked out last week, the new designs use conventional optical components to steer light around central region that is hidden from view. Because these components can easily be made large, the hidden cavity is also big.

Hongsheng and co have used their new designs to cloak fish in water and to partially cloak a cat sitting in front of a projected image.

You can watch videos of these devices here and here.

Their designs are a little more sophisticated than the ones we looked at last week. One is a square cloak with 90 degree symmetry, meaning it hides objects from view in the north, south, east and west directions, say. Another is a hexagonal cloak which hides in six directions.

Of course, view these devices from any other direction and the cloaking fails (although the cloaks can obviously be rotated to make an object disappear in any direction).

Given that these devices are easy to design and cheap to build, it’s not hard to imagine them finding immediate application. Few people need to hide a fish or a cat. So an interesting question is what will they be used for first.

Answers in the comments section, please.

Ref: arxiv.org/abs/1306.1780 : Natural Light Cloaking for Aquatic and Terrestrial Creatures

Keep Reading

Most Popular

conceptual illustration of a heart with an arrow going in on one side and a cursor coming out on the other
conceptual illustration of a heart with an arrow going in on one side and a cursor coming out on the other

Forget dating apps: Here’s how the net’s newest matchmakers help you find love

Fed up with apps, people looking for romance are finding inspiration on Twitter, TikTok—and even email newsletters.

computation concept
computation concept

How AI is reinventing what computers are

Three key ways artificial intelligence is changing what it means to compute.

still from Embodied Intelligence video
still from Embodied Intelligence video

These weird virtual creatures evolve their bodies to solve problems

They show how intelligence and body plans are closely linked—and could unlock AI for robots.

We reviewed three at-home covid tests. The results were mixed.

Over-the-counter coronavirus tests are finally available in the US. Some are more accurate and easier to use than others.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.