Researchers at Columbia Engineering School have demonstrated that light can travel on an artificial material without leaving a trace under certain conditions, technology that would have many applications from the military to telecommunications.

In a study published July 10 on Nature Photonics鈥檚 website, Serdar Kocaman, an electrical engineering Ph.D. candidate, and Chee Wei Wong, associate professor of mechanical engineering, demonstrated how an optical nanostructure can be built that controls the way light bounces off it.
 
When light travels, it bends鈥攊n technical terms, it disperses and incurs 鈥減hase,鈥� an oscillating curve that leaves a trail of information behind it. Those oscillations show an object鈥檚 properties, such as shape and size, which can identify it. However, light hits Kocaman鈥檚 and Wong鈥檚 specially engineered material without leaving a trace.
 
Every natural known material has a positive refractive index: when light hits it, the light bends or refracts. The researchers engineered a structure in which they etched tiny holes, creating a material known as a 鈥減hotonic crystal鈥� which behaves as though it has zero index 鈥� light can travel with an ultrafast velocity in this environment. The material, a coating no thicker than one hundredth of the diameter of a strand of hair, has properties that don鈥檛 occur in nature.
 
鈥淲e鈥檙e very excited about this. We鈥檝e engineered and observed a metamaterial with zero refractive index,鈥� said Kocaman. 鈥淓ven in a vacuum, light propagates with a phase advancement. With the zero phase advancement, what we鈥檝e seen is that the light travels through the material as if the entire space is missing.鈥�
 
鈥淲e can now control the flow of light, the fastest thing known to us,鈥� Wong said. 鈥淭his can enable self-focusing light beams, highly directive antennas, and even potentially an approach to hide objects, at least in the small scale or a narrow band of frequencies.鈥�
 
The zero-index material was based on a negative refractive index material and a superlattice material demonstrated consecutively in 2008 and 2009 by the scientists. In the new paper Kocaman and Wong, together with colleagues, demonstrate that the optical phase advancement can be controlled and even eliminated under certain conditions.
 
The study was led by Wong and Kocaman, in collaboration with scientists at the University College of London, Brookhaven National Laboratory, and the Institute of Microelectronics of Singapore. It is the first time phase and zero-index observations have been made on both a photonic chip scale and at infrared wavelengths. These photonic chip circuits can be helpful in fiberoptic networks.