There’s been some press about the “invisibility cloak” that would become possible with the new metamaterials that can exhibit negative refractive index. There’s an article about a specific “lens” design here at the Japanese Tech On site. The basic idea is just to bend the light rays coming from behind the object and make them go around a bend (the object you want to hide is in the bend) and then straighten them out again so they can continue on their original path as if nothing had happened. So in my understanding the result would not be an invisibility cloak but perhaps something more like a block of glass that appears completely clear from all directions but there is actually an object inside it.
This technology apparently works for other wavelengths, probably even easier to do.
Put the object in the bend on the left side of the circle and it’s invisible – it doesn’t block, reflect or in any way interact with the yellow light rays
This could mean all kinds of trouble in the future. Think what kind of collisions an almost invisible (both to the eye and radar) aircraft could have. You might only need small engine intake and exhaust ports to be seen. Or people entering forbidden places inside a cylinder shaped “invisibility can”. The technology, if realized, will probably be heavy, limited to certain shapes and visually quite imperfect though.