Light for future optical technologies: successful conclusion of the TRR 142 Collaborative Research Centre

35 million euros, 210 scientists, 12 years of research: after the maximum duration of three funding periods, the Transregional Collaborative Research Centre TRR 142 'Tailor-made non-linear photonics: From fundamental concepts to functional structures' is officially winding down in December 2025. Scientists at Paderborn University and TU Dortmund University have achieved great things and literally shone a light into darkness with their research contributions. The experts have developed materials that are smaller than the wavelength of light and managed to precisely manipulate, control and even teleport tiny light particles known as photons. They have created quantum light sources – vital tools for quantum computing and ultra-fast communication – and low-temperature electronics to control quantum experiments. And these are a just a few examples of their work. Above all, they have made a vital contribution to fundamental international research into optical systems. This means that the scientists have paved the way for more efficient optical components and new technologies for the long term.

Non-linear effects

The aim of the Transregional Collaborative Research Centre (TRR) was to research, develop and construct what are known as non-linear photonic systems. In simple terms, these are changes to light waves that do not occur in nature, i.e. in everyday life. Natural optical phenomena are linear. When light and material interact, linear effects change the incident light. Examples include reflection or dispersion. However, the wavelengths always stay the same. Lasers operate differently: they enable the creation of non-linear effects, such as frequency doubling, where the wavelength is half that of the original light. TRR 142 has created concepts to take innovative non-linear functionalities from the fields of material physics and quantum photonics and make them usable for future information and communication technology applications.

From fundamentals to practical application

The scientists drew on state-of-the-art technological facilities to research new physical properties and devices based on tailor-made, strong non-linearities and real quantum effects. 'We wanted to take non-linear optical and quantum effects from fundamental physical research studies and put them to practical use', said Professor Thomas Zentgraf, a member of the Department of Physics at Paderborn University and the TRR's spokesperson. To achieve this, the project combined the core competencies of Paderborn University in the fields of photonic materials, solid-state technology, quantum optics and theory with those of TU Dortmund University in non-linear spectroscopy and instrumentation. The team focused on tailoring non-linear interactions, the control of quantum systems, light emission and propagation, and non-linearities at the single-photon level – which subsequently proved to be genuinely pioneering work.

Tap-proof communications thanks to manipulation

One prominent application of the TRR's research is encrypted, tap-proof communications, thanks to findings from the field of photonic research. Scientists made targeted changes to, for example, optical properties (i.e. light diffusion and transmission) in order to encode the data being transported. To achieve this, they developed 'metasurfaces': synthetic components that affect light waves. Previously, these materials were not intended or well-researched enough for efficient use. 'They consist of synthesised structures with optical, magnetic or electrical properties that do not occur in nature. The benefit of these is that they can refract and even alter rays', Professor Zentgraf explained. 'This can be used to achieve new frequencies that would not have been possible without targeted manipulation.'

Pioneering work in integrated optics

This arrangement of nanostructures on surfaces then allowed the creation of synthetic materials whose linear and non-linear behaviour could be customised. Their functionality far exceeds that of conventional materials. This enables compact optical components for frequency conversion or light propagation control. Research in the field of quantum photonics focused on quantum communications, quantum sensor technology and quantum information processing. One key foundation for these projects was provided by pioneering technological work in the field of integrated optics, such as the development of efficient waveguides for frequency conversion. The targeted use of these technological developments enabled the implementation of integrated optical frequency converters, quantum light sources and non-linear interferometers, all of which are crucial key elements of optical quantum technologies.

Milestones: quantum dots and quantum teleportation

Quantum technologies offer many innovative new ways of processing and transmitting information and conducting precise measurements. As protecting sensitive data and information has become increasingly vital, communication networks are similarly gaining in importance. Semiconductor quantum dots also play a crucial role in this area. These are tiny structures that behave like artificial atoms. With precise laser excitation, they can control individual photons with great accuracy and achieve single photon sources – an essential basis for absolutely secure communication with quanta. As well as producing such structures, Paderborn's physicists also managed to achieve what is known as quantum teleportation with 'imperfect quantum dots', in other words artificial material structures. This involves transferring the state of one photon to another. The sender and recipient are entangled. This requires sources that can produce indistinguishable protons.

Research for the photonics of the future

'This close collaboration between two outstanding partners in solid-state physics and optical spectroscopy has created a strong alliance devoted to researching and developing the non-linear photonics of the future. We were able to use the latest theoretical approaches and innovative experimental methods to examine fundamental physical questions and new component designs – based on tailor-made non-linearities and fundamental quantum effects', Professor Zentgraf noted. The results achieved together stand as milestones on the path towards future information technologies and those already at the evaluation stage, such as quantum communications or optical quantum information processing. TRR 142 has thus laid the foundations for achieving technological sovereignty in order to open up new markets for pioneering optical technologies.

Collaborative Research Centres are long-term university-based research institutions in which researchers work together within a multidisciplinary research programme. They allow researchers to tackle innovative, challenging, complex and long-term research undertakings through the coordination and concentration of individuals and resources within the applicant universities. They are funded by the German Research Foundation (DFG) for a maximum of 12 years, with each funding period covering four years.

More information about the TRR is available at: https://trr142.uni-paderborn.de/en/

Provided by Paderborn University