6 months ago
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Finding new ways to slow fleeting waves of light or even stop them in their tracks could lead to more advanced photonic devices, such as lasers, LED displays, fiber-optics, and sensors.
In a cunning trap made from a silicon crystal tweaked to behave as if it's deformed, scientists have found a flexible new way to make light waves stand absolutely still.
Light can be brought to a halt in a few different ways, such as by cooling clouds of atoms or even braiding light waves together. This new method, from AMOLF and Delft University of Technology in the Netherlands, has advantages that could bring new technological applications to reality.
"This principle offers a new approach to slow down light fields and thereby enhance their strength," says physicist Ewold Verhagen of AMOLF. "Realizing this on a chip is particularly important for many applications."
The team's work was based on manipulating electrons using two-dimensional materials such as graphene. In a conducting material, electrons can move freely, zooming along like a tiny highway. However, applying a magnetic field can restrict movement of the electrons to certain energies, known as Landau levels.
It's not only magnets that push electrons to Landau levels. Two-dimensional graphene, consisting of a single layer of atoms, can do it too. Normally, graphene is conductive; but if you warp or distort the graphene, such as by stretching it, you can confine the electrons to Landau levels, turning the normally conductive material into an insulator.
Together with René Barczyk of AMOLF and Kobus Kuipers of Delft University, Verhagen sought to find out if they could find a material that had a similar effect on photons to the one that warped graphene has on electrons.
Now, light can be manipulated with a similar material to graphene, called a photonic crystal. And the researchers found that they could stall light waves in a similar fashion.
"A photonic crystal normally consists of a regular – two dimensional – pattern of holes in a silicon layer. Light can move freely in this material, just like electrons in graphene," Barczyk explains.
"Breaking this regularity in exactly the right manner will deform the array and consequently lock the photons. This is how we create Landau levels for photons."
The team's honeycombed photonic crystals were able to confine light to Landau levels using a process that represented different kinds of deformation, such as curving or warping. And they were even able to induce different types of warping at different places in the same material, resulting in a photonic crystal in which light can flow freely in some parts, but becomes confined in others.
The discovery requires further development, but it does bring scientists a step closer to the fine control of light on very small scales.
"This brings on-chip applications closer," says Verhagen.
"If we can confine light at the nanoscale and bring it to a halt like this, its strength will be enhanced tremendously. And not only at one location, but over the entire crystal surface. Such light concentration is very important in nanophotonic devices, for example for the development of efficient lasers or quantum light sources."
The team's research has been published in Nature Photonics.
