For those dreaming that the Star Trek technology of cloaking will one day become reality, they can take note of the steady progress that real-world cloaking technology has been making. The goal of cloaking research is to find ways to redirect light around a shape, from all directions, in essence making it so the shape disappears to the naked eye. Scientists have had success working with nanoscale objects using special lenses.
Cloaking science or "transformation optics" as its more formally called has until now relied on exotic "metamaterials" to redirect light. However, a breakthrough from Purdue University has created a "tapered optical waveguide" that accomplishes the same behavior at a lower cost and without using exotic compounds.
The new cloak is not only cheaper, it also performs better -- it can cloak an area of up to 100 times the wavelengths of a laser, while previous designs only managed a few times the wavelengths. Additionally, where metamaterials could only cloak part of the spectrum, this design can cloak light from a variety of wavelengths.
Vladimir Shalaev, Purdue University's Professor of Electrical and Computer Engineering, used it to cloak objects up to 50 microns -- the size of a human hair. The cloak consisted of two thin gold layers -- one flat, on bottom, and another on top of the cloaked object. The top layer was curved to act as a "hyperlense" an optical instrument with extraordinary capabilities.
Professor Shalaev describes the breakthrough, stating, "All previous attempts at optical cloaking have involved very complicated nanofabrication of metamaterials containing many elements, which makes it very difficult to cloak large objects. Here, we showed that if a waveguide is tapered properly it acts like a sophisticated nanostructured material. Instead of being reflected as normally would happen, the light flows around the object and shows up on the other side, like water flowing around a stone."
Hyperlenses, like this superb new one from Purdue, promise to revolutionize many fields of optics. Where typical materials bend light -- a phenomenon known as refraction -- they keep its original direct with respect to a perpendicular line from the surface. Hyperlenses, however, can actually have an index of refraction of less than 0, allowing the light to reverse direction. Cloaking devices take advantage of this behavior to curve light around objects.
The lenses could revolutionize optical computing, create super-microscopes able to image DNA, cloak objects, and much more.
The new work raises hopes of large-scale cloaks (think Harry Potter's Invisibility Cloak), as it enables one device to cloak many wavelengths, unlike past work which would have necessitated many devices. There has been no derived theoretical size limit for objects cloaked, so large scale cloaking may be possible as cloaking devices are refined.
The research appears in the May 29 edition of the journal Physical Review Letters.
The paper was co-authored by other researchers on the project -- Igor I. Smolyaninov, a principal electronic engineer at BAE Systems in Washington, D.C.; Vera N. Smolyaninova, an assistant professor of physics at Towson University in Maryland; Alexander Kildishev, a principal research scientist at Purdue's Birck Nanotechnology Center. BAE fabricated the device to cloak the objects, based on the Purdue team's theoretical work.