The Vietnamese Ph.D. candidate Quyet Ngo investigates optical fibers.

The Art of Giving Light another Color

A team of physicists has developed optical fibers that can do more than just direct light.
The Vietnamese Ph.D. candidate Quyet Ngo investigates optical fibers.
Image: Jens Meyer (University of Jena)
  • Light

Published: | By: Angelika Schimmel, English translation by Gleb Chupakhin

Red does not turn green and infrared light does not suddenly become visible when it is sent through a light conductor. Light does not change its wavelength quite so easily, except when a certain trick is used. An international team of researchers has now, for the first time, effectively applied this trick to optical fibers. The team was the first to successfully functionalize optical fibers so that the fibers transform invisible infrared light into red light. The researchers' special fibers could be used in the future as miniature light converters. The discovery was made possible by the collaboration of four working groups of the SFB/CRC 1375 NOA with partners at the Fraunhofer IOF, Leibniz IPHT and the Universities of Sydney and Adelaide in Australia. The male and female scientists of the "Photonics in 2D Materials" research division led by ACP PI Dr. Falk Eilenberger were recently able to publish their research results in "Nature Photonics". The first author is Ph.D. candidate Quyet Ngo.

Computers, mobile phones and supercomputing centers are constantly becoming more powerful. Unimaginable amounts of data are processed in increasingly smaller amounts of time. As a negative consequence, the energy use of the chips that realize this computing potential is also becoming immeasurably large. According to a report from the Borderstep Institute for Innovation and Sustainability GmbH, the computing centers in Germany alone used sixteen billion kilowatt-hours of energy during the pandemic year 2020. “The problem is that chips with common semiconductor materials use close to 50 percent of the energy just to move information using electrons. If we find a data transporter that is more energy-effective than electrons, a mobile phone’s battery could function for longer before needing to be charged again”, says Dr. Falk Eilenberger, director of the research group “Photonics in 2D-Materials” at the Institute for Applied Physics at ACP. This improvement would happily be exploited by all mobile phone users, not to mention by the computing centers and servers critical for cloud computing and video streaming that could save millions of kilowatt-hours.

New Roles for Light as a Tool

For this and other reasons, colleagues of Falk Eilenberger are on the search for alternatives to the energy-guzzling electrons. The researchers are setting their sights on photons as a medium – for data transport as well – and on light conductors made of glass. However, simple light-conducting fibers are not up to the task. The fibers must be specially constructed and “upgraded”  in order to perform the new functions. The team in Eilenberger’s research division and primarily the Ph.D. candidate Quyet Ngo uses so-called 2D-materials – materials made of a single layer of atoms – for this purpose.

“Our idea was to change the characteristics of light with the help of these new materials”, Ngo explains – for example the light’s wavelength and therefore its color. “Normally, light doesn’t change its color”, complements Falk Eilenberger. “Except if a lot of light interacts with special materials such as certain crystals”. Unfortunately, these crystals are difficult to handle.

2D-materials are a better alternative for the Jena team. “Specifically, we have experimented with a very old material, molybdenum disulfate”, says Quyet Ngo. This material has been used for a long time already as a lubricant in motor oils. In Jena, a method has been found to use this material for a new, high-tech assignment: to change the characteristics of light.

Growing High-tech Materials

For this, the researchers had to modify the light conducting fibers as well. They used specially formed fibers developed by Prof. Dr. Markus Schmidt’s research team at the IPHT in Jena and Prof. Dr. Heike Heidepriem-Ebendorff at the University of Adelaide. “These fibers are shaped like a hollow “C”, which causes the light to be driven more along the surface than in the middle”, explains Ngo. This eases the interaction of the light particles with the 2D-material. Following the Jena experimental protocol, this material is not created separately and then applied to the glass fibers using a complicated method, but rather is grown directly in its depression – like in a Petri dish.

The reactor in which this occurs at temperatures of around 700 degrees centigrade is located at the Institute of Physical Chemistry of the University of Jena. “Here, we could use the research results of Prof. Dr. Andrey Turchanin, who developed the technology that allows for the new 2D-materials to be effectively grown on a large scale”, says Falk Eilenberger. “Only through the combination of the special fibers from the IPHT, the 2D-materials from the Institute for Physical Chemistry and the technical solutions from the Eilenberger research group was the result that lies before us today possible”, complements Andrey Turchanin. In addition, research results from the Universities of Sydney and Adelaide supported the effort. In total, fifteen people from six institutions worked together on the topic.

“Using the glass fibers carrying an extremely thin layer of molybdenum disulfate, we were able to change infrared light into red light. We send the light with a wavelength of 1240 nanometers through the fibers and it comes out with a wavelength of 620 nanometers at the end”, explains Ngo. In this way, the Jena researchers have become the first globally to successfully functionalize optical fibers in such a way that they could be used in the future as non-linear light converters.

New Technology Offers New Chances for Laser Technology

Falk Eilenberger is convinced that to be able to change light in such a way offers new possibilities, for example in the field of laser technology – especially in Jena, where lasers are a big subject. “I think that our technology will be applied in a diversity of ways here in the toolbox of optical fibers.” The advantages are easy to see: the technology functions at room temperature, the material is chemically robust, straightforward to manipulate and displays interesting characteristics. It may be possible to grow the material in multiple layers on the fibers or to modify it further to allow for more interactions with light. Quyet Ngo, who will thoroughly describe the current research results in his doctoral thesis, wants to explore the possibility of using the new material in sensor technology in the near future.

Regarding the problem of energy-guzzling chips mentioned at the beginning, Eilenberger and Ngo are optimistic: “That which grows on glass can also grow on silicon”. For them, it’s not utopian to envision the use of photons instead of electrons for digital data transfer.


Original Publication:

Gia Quyet Ngo et al.: In-fibre second-harmonic generation with embedded two-dimensional materials, Nature Photonics 1 September 2022, DOI: 10.1038/s41566-022-01067-y. URL:


Photonics in 2D-Materials
Falk Eilenberger, Dr
Research Group Leader
IAP, Room 313
Albert-Einstein-Straße 15
07745 Jena
Photonics in 2D-Materials
Gia Quyet Ngo
PhD Student
IAP, Room 315
Albert-Einstein-Straße 15
07745 Jena