Bending light around tight corners without backscattering losses

November 19, 2018 by Ken Kingery, Duke University
Schematic of the new optical waveguide device showing the input and output gratings and silicon waveguide connections. Credit: Natasha Litchinitser, Duke University

Engineers at Duke University have demonstrated a device that can direct photons of light around sharp corners with virtually no losses due to backscattering, a key property that will be needed if electronics are ever to be replaced with light-based devices.

The result was achieved with photonic crystals built on the concept of topological insulators, which won its discoverers a Nobel Prize in 2016. By carefully controlling the geometry of a crystal lattice, researchers can prevent light traveling through its interior while transmitting it perfectly along its surface.

Through these concepts, the device accomplishes its near-perfect transmittance around corners despite being much smaller than previous designs.

The Semiconductor Industry Association estimates that the number of electronic devices is increasing so rapidly that by the year 2040, there won't be enough power in the entire world to run them all. One potential solution is to turn to massless photons to replace the electrons currently used for transmitting data. Besides saving energy, photonic systems also promise to be faster and have higher bandwidth.

Photons are already in use in some applications such as on-chip photonic communication. One drawback of the current technology, however, is that such systems cannot turn or bend light efficiently. But for photons to ever replace electrons in microchips, travelling around corners in microscopic spaces is a necessity.

Closer look at the new optical waveguide device featuring a zoomed-in view of the fabricated photonic crystal topological insulator. Credit: Natasha Litchinitser, Duke University
"The smaller the device the better, but of course we're trying to minimize losses as well," said Wiktor Walasik, a postdoctoral associate in electrical and computer engineering at Duke. "There are a lot of people working to make an all-optical computing system possible. We're not there yet, but I think that's the direction we're going."

Previous demonstrations have also shown small losses while guiding photons around corners, but the new Duke research does it on a rectangular device just 35 micrometers long and 5.5 micrometers wide—100 times smaller than previously demonstrated ring-resonator based devices.

In the new study, which appeared online on November 12 in the journal Nature Nanotechnology, researchers fabricated topological insulators using electron beam lithography and measured the light transmittance through a series of sharp turns. The showed that each turn only resulted in the loss of a few percent.

"Guiding light around sharp corners in conventional was possible before but only through a long laborious process tailored to a specific set of parameters," said Natasha Litchinitser, professor of electrical and computer engineering at Duke. "And if you made even the tiniest mistake in its fabrication, it lost a lot of the properties you were trying to optimize."

The central part of the new photonic crystal topological insulator waveguide, with the path of a photon's path highlighted in green. The experiment showed that each turn resulted in backscattering losses of only a few percent. Credit: Natasha Litchinitser, Duke University
"But our device will work no matter its dimensions or geometry of the photons' path and photon transport is 'topologically protected,'" added Mikhail Shalaev, a doctoral student in Litchinitser's laboratory and first author of the paper. "This means that even if there are minor defects in the photonic crystalline structure, the waveguide still works very well. It is not so sensitive to fabrication errors."

The researchers point out that their also has a large operating bandwidth, is compatible with modern semiconductor fabrication technologies, and works at wavelengths currently used in telecommunications.

The researchers are next attempting to make their waveguide dynamically tunable to shift the bandwidth of its operation. This would allow the waveguide to be turned on and off at will—another important feature for all-optical photon-based technologies to ever become a reality.

Explore further: Trapping light that doesn't bounce off track for faster electronics

More information: Mikhail I. Shalaev et al, Robust topologically protected transport in photonic crystals at telecommunication wavelengths, Nature Nanotechnology (2018). DOI: 10.1038/s41565-018-0297-6

Related Stories

Nanocrystals emit light by efficiently 'tunneling' electrons

July 23, 2018

Using advanced fabrication techniques, engineers at the University of California San Diego have built a nanosized device out of silver crystals that can generate light by efficiently "tunneling" electrons through a tiny barrier. ...

Capturing light in a waveguide array

June 4, 2018

Cheaper and more efficient photonic devices, such as lasers, optical fibers, and other light sources may be possible with confined light that is unaffected by imperfections in the material that confines it, according to new ...

First step towards photonic quantum network

January 25, 2017

Advanced photonic nanostructures are well on their way to revolutionising quantum technology for quantum networks based on light. Researchers from the Niels Bohr Institute have now developed the first building blocks needed ...

Recommended for you

Team invents method to shrink objects to the nanoscale

December 13, 2018

MIT researchers have invented a way to fabricate nanoscale 3-D objects of nearly any shape. They can also pattern the objects with a variety of useful materials, including metals, quantum dots, and DNA.

Engineers produce smallest 3-D transistor yet

December 10, 2018

Researchers from MIT and the University of Colorado have fabricated a 3-D transistor that's less than half the size of today's smallest commercial models. To do so, they developed a novel microfabrication technique that modifies ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

FredJose
not rated yet Nov 20, 2018
Mmmmhhhh, Lightsaber, anyone?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.