Photonic Topological Insulator Demonstrated

A device protecting the transport of light through a unique honeycomblike lattice structure of helical waveguides has demonstrated the photonic equivalent of a topological insulator. The discovery could bring us a step closer to quantum computing, the researchers say.

As computers get faster and chips get denser, there is a need for smaller devices that manipulate light. However, as devices get smaller, imperfections in the fabrication processes can make light move irregularly and unpredictably.

To prevent unwanted scattering from any kind of defect, researchers at Technion-Israel Institute of Technology, led by professor Mordechai Segev in collaboration with colleagues from Friedrich-Schiller University in Jena, Germany, have developed an optical lattice of helical waveguides, demonstrating the first photonic Floquet topological insulator. The device “topologically protects” light, meaning that light flows uninterrupted despite the presence of defects.

Topological protection was first conceived not for light but for electrons flowing in a solid material. However, Technion’s Dr. Mikael Rechtsman and Yonatan Plotnik discovered a way to bring topological protection into photonics using an array of helical, or spiral-shaped, waveguides that interact with one another.

“The helical nature of the waveguides breaks the symmetry, so that in the forward direction, the waveguides are spinning clockwise, and in the backward direction, counterclockwise,” Rechtsman said. “In our procedure, this is an essential ingredient in preventing unwanted scattering.”

These structures may provide a new platform for understanding and probing the properties of photonic topological insulators, Rechtsman said. “For example, all sorts of experiments that would be difficult or impossible to carry out in solid-state materials can now be accessed using light.”

“This discovery is another step in the progress towards optical and quantum computing,” said Julia Zeuner, a graduate student at Friedrich-Schiller University in Jena, who fabricated the sophisticated photonic structure and did part of the experiments.

“We have discovered a completely novel phenomena, and new phenomenon are destined to find applications in directions that we can't even imagine,” Segev said.

The findings appeared in Nature (doi: 10.1038/nature12066).

For more information, visit: www1.technion.ac.il/en