Now two different cloak designs have managed to conceal bumps over the full visible spectrum. Chris Gladden and Majid Gharghi of the University of California, Berkeley, etched holes into a thin layer of silicon nitride deposited on porous glass. Varying the diameter of the holes between 20 and 65 nanometres – smaller than the wavelengths of visible light – changed the way the layer refracted light, allowing its interaction with the porous glass substrate to cloak a small bump
The Berkeley demonstration "is an excellent and significant advance over their previous work in the infrared", says George Barbastathis of the Singapore-MIT group. But he says that using a natural material like calcite offers a big advantage over nano-fabrication. "Our cloak is about 10,000 times bigger than the Berkeley cloak, and also, I estimate, more than 10,000 times cheaper."
Think of it as invisibility cloaks 2.0.