University at Buffalo engineers have created 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.
They developed a hyperbolic metamaterial waveguide, which is an advanced
microchip made of alternate ultra-thin films of metal and semiconductors and
insulators. The waveguide halts and ultimately absorbs each frequency of light,
at slightly different places in a vertical direction, to catch series of
wavelengths.
Electromagnetic absorbers have been studied for many years, especially
for military radar systems. 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.
Ultra-thin films are developed
that will slow the light and therefore allow much more efficient absorption. Light
is made of photons; because they move extremely fast are difficult to control.
In their initial attempts to slow light, researchers relied upon cryogenic
gases. But because cryogenic gases are very cold, this process is not
industrially feasible.
Earlier researchers made nano-scale-sized grooves in metallic surfaces
at different depths, which altered the optical properties of the metal. While
the grooves worked, they had limitations; the energy of the incident light
cannot be transferred onto the metal surface efficiently, which hindered its
use for practical applications. The hyperbolic metamaterial waveguide solves
that problem because it is a large area of patterned film that can collect the
incident light efficiently. It is referred to as an artificial medium with
subwavelength features whose frequency surface is hyperboloid, which allows it
to capture a wide range of wavelengths in different frequencies including
visible, near-infrared, mid-infrared, terahertz and microwaves.
It could lead to advancements in an array of fields. For example, in
electronics there is a phenomenon known as crosstalk, in which 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.
The on-chip absorber may also be applied to solar panels and other
energy-harvesting devices. It could be especially useful in mid-infrared
spectral regions as thermal absorber for devices that recycle heat after
sundown.
Technology such as the Stealth bomber involves materials that make
planes, ships and other devices invisible to radar, infrared, sonar and other
detection methods. 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.
For further reading: http://www.nature.com/srep/2013/130213/srep01249/full/srep01249.html
