Last month, researchers Yuan Wang, Zi Jing Wong and Xiang Zhang of the University of California at Berkeley announced an optical "invisibility cloak", which everyone latched on to as the embodiment of the fictional cloak used by Harry Potter. The device does work at optical frequencies: specifically deep red light (730 nanometer) and it's currently only microscopic in size, though, so it's not able to hide you or your stuff.
Zhang and team tested their invention by wrapping the cloak around a cell-sized object with a highly irregular shape. As expected, when red light struck the cloak, it reflected off its surface as if off a flat mirror, making the object beneath it invisible even by phase-sensitive detection. When the polarization of the nanoantennas was changed, the cloaking effect stopped entirely.The principle seems to be related to that microwave cloak mentioned above. Antennas are fabricated on the base layer structure and the electromagnetic fields of the light are guided in the desired direction. This cloak looked like a flat mirror. There's a video of the cloak being demonstrated on Gizmag, shot through a microscope. The material of the cloak is incredibly thin, barely 3 millionths of an inch, and none of the few articles I could find mentioned how they made the antennas, aside from calling it "nanofabrication". Maybe that's the secret sauce.
Unlike previous attempts at an invisibility cloak, this design is scalable — able to cover larger objects without increasing the thickness of the cloak, and able to conceal objects that have sharp edges and peaks. "Maybe in the future, people can use this as decoration or a wearable," Xingjie Ni, an assistant professor at Pennsylvania State University, who conceived the research idea and led the team, told MashableI don't think this something to get super excited about, but it's definitely a step in the right direction. I believe we'll eventually see those full spectrum cloaks that hide real world sized objects, but it will still be a while.