Search
Menu
AdTech Ceramics - Ceramic Packages 1-24 LB

Topology Protects Light Propagation in Photonic Crystal

Facebook X LinkedIn Email
A team from the research institute AMOLF and Delft University of Technology (TU Delft) observed light propagation within a photonic crystal without the usual distortion caused by reflections. Because the crystal consists of two parts, each with a slightly different pattern of perforations, light can propagate along the boundary between the two parts in such a way that it is “topologically protected,” and therefore does not bounce back at imperfections. Even when the boundary forms a sharp corner, the light follows it without a problem.

AMOLF's Ewold Verhagen and TU Delft's Kobus Kuipers are two of the researchers investigating a new class of electronic materials known as topological insulators. While most materials are either conductive for electrons or not, topological insulators exhibit a different kind of conduction altogether.

“The inside of a topological insulator does not allow electron propagation, but along the edge, electrons can move freely,” Verhagen said. “Importantly, the conduction is topologically protected; the electrons are not impacted by disorder or imperfections that would typically reflect them. So the conduction is profoundly robust.”

Scientists have long sought to replicate this behavior for light conduction. “We really wanted to accomplish topological protection of light propagation at the nanoscale, and thus open the door to guiding light on optical chips without its being hindered by scattering at imperfections and sharp corners,” Verhagen said.

The researchers used two-dimensional crystals with two slightly different hole patterns. The “edge” that enables light conduction is the interface between the two hole patterns.

“Light conduction at the edge is possible because the mathematical description of light in these photonic crystals can be described by specific shapes, or more accurately, by topology,” Kuipers said. “The topology of the two different hole patterns differs, and precisely this property allows light conduction at the boundary, similar to electrons in topological insulators. Because the topology of both hole patterns is locked, light conduction cannot be revoked; it is topologically protected.”

DataRay Inc. - ISO 11146-Compliant

When the researchers imaged light propagation with a microscope, they saw that it behaved as predicted. Moreover, they witnessed the topology, or mathematical description, in the observed light.

"For these light waves, the polarization of light rotates in a certain direction, analogous to the spin of electrons in topological insulators,” Kuipers said. “The spinning direction of light determines the direction in which this light propagates. Because polarization cannot easily change, the light wave can even flow around sharp corners without reflecting or getting scattered, as would happen in a regular waveguide.”

By using silicon chips and light of a similar wavelength as used in telecommunication, Verhagen expects to increase the application prospects.

“We are now going to investigate if there are any practical or fundamental boundaries to topological protection and which functionalities on an optical chip we could improve with these principles,” Verhagen said. “The first thing we are thinking of is to make the integrated light sources on a photonic chip more reliable. This is important in view of energy-efficient data processing or green ICT [information and communications technology]. Also, to efficiently transfer small packages of quantum information, the topological protection of light can be useful.”

The research was published in Scientific Advances (www.doi.org/10.1126/sciadv.aaw4137). 

Published: March 2020
Glossary
topology
Topology is a branch of mathematics that focuses on the properties of space that are preserved under continuous deformations, such as stretching, crumpling, and bending, but not tearing or gluing. Topology studies the intrinsic properties of objects and spaces that remain unchanged even when the objects undergo transformations. The key concept in topology is that of continuity, and it is concerned with understanding the spatial relationships and structures that persist despite deformations. ...
quantum
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
Research & TechnologyAMOLFTU Delftphotonic crystaltopologyphotonic chipquantumquantum topologycrystalsMaterialsTech Pulse

We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.