Buffalo University researchers have created an advanced waveguide which could lead to breakthroughs in stealth technology and solar energy. Their hyperbolic metamaterial waveguide is basically a sophisticated microchip made from alternating ultra-thin films of metal and semiconductors and/or insulators. The waveguide stops and eventually absorbs every light frequency, at somewhat different points in a vertical axis, to capture a rainbow of wavelengths.
“Electromagnetic absorbers have been studied for many years, especially for military radar systems,” said Qiaoqiang Gan, PhD, an assistant professor at UB,. “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 ultra-thin films with tunable absorption band.”
“We are developing ultra-thin films that will slow the light and therefore allow much more efficient absorption, which will address the long existing challenge.”
Cryogenic Gases and Nanoscale Grooves
Light is made of photons that are difficult to control, since they move at the speed of light. In their first attempts to slow light, researchers depended on cryogenic gases. But cryogenic gases are very cold, roughly 240 degrees below zero Fahrenheit, and hard to work with outside a laboratory setting.
Dr. Gan previously helped develop a way to slow light without using cryogenic gases. He and a team of researchers at Lehigh University made nano-scale-sized grooves in metallic surfaces at different depths, a process that altered the optical properties of the metal. While the grooves worked, they had limitations. For instance, the energy of the incident light cannot be transferred onto the metal surface efficiently, which hampered its use for practical applications, according to Gan.
The problem is solved by the hyperbolic metamaterial waveguide. It is a big area of patterned film that can collect the incident light efficiently, and is referred to as an artificial medium with subwavelength features. Their frequency surface is hyperboloid, which lets it capture a wide range of wavelengths in different frequencies including visible, near-infrared, mid-infrared, terahertz and microwaves.
Potential Fields of Advancement
There is a phenomenon in electronics called crosstalk, where a signal transmitted on one circuit or channel creates an undesired effect in another circuit or channel. The on-chip absorber could potentially prevent this.
An on-chip absorber could also be applied to solar panels and other energy-harvesting devices. It would be especially useful in mid-infrared spectral regions as thermal absorber for devices that recycle heat after sundown, Gan said.
Since the on-chip absorber has the potential to sop up different wavelengths at a huge amount of frequencies, it could be useful as a stealth coating material for aircraft or ships.
Haifeng Hu, Dengxin Ji, Xie Zeng, Kai Liu & Qiaoqiang Gan Rainbow Trapping in Hyperbolic Metamaterial Waveguide Scientific Reports 3, Article number:1249 doi:10.1038/srep01249
Tsakmakidis, K. L., Boardman, A. D. & Hess, O. Trapped rainbow storage of light in metamaterials. Nature 450, 397–401 (2007)
Prade, B., Vinet, J. Y. & Mysyrowicz, A. Guided optical waves in planar heterostructures with negative dielectric-constant. Phys. Rev. B 44, 13556–13572 (1991).
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