Catching rainbows just got easier with an advanced waveguide that slows light. The advancement in photonics could lead to technological breakthroughs in solar energy, stealth technology and other areas of research. The “hyperbolic metamaterial waveguide,” developed by Dr. Qiaoqiang Gan and graduate students at the University at Buffalo, is an advanced microchip made of alternating ultrathin films of metal and semiconductors and/or insulators. The waveguide halts and ultimately absorbs each frequency of light, at slightly different places in a vertical direction, to catch a “rainbow” of wavelengths. “Electromagnetic absorbers have been studied for many years, especially for military radar systems,” said Gan, an assistant professor of electrical engineering and a researcher at the university’s new Center of Excellence in Materials Informatics. “Right now, researchers are developing compact light absorbers based on optically thick semiconductors or carbon nanotubes. However, it is still challenging to realize the perfect absorber in ultrathin films with tunable absorption band.” An up-close look at the “hyperbolic metamaterial waveguide” developed at the University at Buffalo, which catches and ultimately absorbs wavelengths in a vertical direction. Images courtesy of University at Buffalo. The investigators now are developing ultrathin films that will slow light, which addresses the long-existing challenge of realizing more efficient absorption, he said. Photons move extremely fast and are difficult to tame. In their initial attempts to slow light, researchers relied on cryogenic gases; however, these gases are so cold — roughly −240 ºF — that they are difficult to work with outside a laboratory. Before joining the University at Buffalo, Gan helped pioneer a way to slow light without cryogenic gases. He and colleagues at Lehigh University made nanoscale-sized grooves in metallic surfaces at different depths, a process that altered the optical properties of the metal. (See: Slow Light Slowed Even More) The grooves worked, but they had limitations. For example, the energy of the incident light cannot be transferred onto the metal surface efficiently, hindering its use for practical applications, Gan said. The hyperbolic metamaterial waveguide solves that problem because it is a large area of patterned film that collects incident light efficiently. The waveguide is referred to as an artificial medium with subwavelength features whose frequency surface is hyperboloid, allowing it to capture a range of wavelengths in different frequencies, including visible, near- and mid-infrared, terahertz and microwaves. Qiaoqiang Gan, assistant professor of electrical engineering, and his colleagues have developed a more efficient way to catch rainbows, an advancement in photonics that could lead to technological breakthroughs in solar energy, stealth technology and other areas of research. The on-chip absorber could be used in a variety of applications. For instance, in electronics the device could prevent crosstalk, a phenomenon in which a signal transmitted on one circuit or channel creates an undesired effect in another circuit or channel. The technology may also be applied to solar panels and other energy-harvesting devices. It could be especially useful in mid-infrared spectral regions as a thermal absorber for devices that recycle heat after sundown, Gan said. Because the on-chip absorber has the potential to absorb different wavelengths at a multitude of frequencies, it could be useful as a stealth coating material. The study appeared in Scientific Reports (doi: 10.1038/srep01249). For more on Gan’s research, see: A Rainbow for the Palm of Your Hand For more information, visit: www.buffalo.edu