Professor Dr Malte Gather: Research works for new optical applications

Malte Gather heads the Humboldt Centre for Nano- and Biophotonics at the University of Cologne. He combines basic research in photonics with targeted applications in medicine, sensor technology, and industry, and is translating key optical technologies from the laboratory into market-ready solutions through innovative polariton filters.

1. What role has transfer played in your career so far?

Early in my career, I worked on projects that took key findings from basic research and translated them into clinical and industrial applications. My aim is to combine basic research with specific applications, be it for medical diagnostics, new display technologies, or innovative optical sensors. Today, my team and I support several spin-offs and collaborative projects with partners in industry and medicine. Knowledge transfer is a key integral part of my scientific work.

2. Which of your transfer activities would you like to report on, and what can you tell us about them?

In recent years, my team has developed a new type of optical filter, which we are currently bringing to market, with a particular focus on applications in microscopy and sensor technology. Until now, it was considered nearly impossible to produce optical filters that reliably separate light of different colours while maintaining consistent properties regardless of the angle of incidence. This problem is known as the ‘dispersion limit of thin-film optics’.

Separating light of different colours is crucial for a wide range of technical applications. Applications range from microscopy and biosensor technology to optical distance measurements in autonomous vehicles and satellite-based weather observation. Such systems are often designed to be highly compact – for example, to integrate an additional optical sensor into a small smartwatch. In ultra-compact optical systems of this kind, the problem frequently arises that light rays strike the filter, which is meant to separate them by colour, at a wide range of angles. This is precisely where our new ‘polariton filters’ offer a solution, as they can filter light almost independently of the angle while maintaining excellent quality.

3. How did you come up with your research topics?

My group has been working for many years on research into lasers made of organic materials, for example so-called "polariton lasers". To analyse their properties, we often measure the dispersion relation. In simple terms, it measures how much light of each colour a laser reflects when it is illuminated with white light at different angles. A few years ago, we discovered that under certain conditions this dispersion becomes very ‘flat’, meaning that the colour of the reflected light depends very little on the angle of incidence.

We then explored whether this property could be utilized for technical applications. Polariton lasers themselves are not effective optical filters: the incident light is mostly absorbed or reflected, regardless of its colour. However, we can now adapt these structures in such a way that they block specific colours of light extremely efficiently, allowing no more than one photon in a million to pass, while simultaneously transmitting over 95 percent of the light of the desired colour.

4. What concrete social impact have you achieved through this activity so far?

With financial support from the European Research Council through an ERC Advanced Grant and a Proof of Concept Grant, as well as from federal funding programmes such as GoBio and EXIST Research Transfer, we are able to focus on specific, socially relevant aspects of our invention.

For instance, we equip our polariton filters with affordable yet powerful camera chips, like those used in modern smartphones. We aim to develop an ultra-compact fluorescence microscope capable of analysing biological samples, for example to detect certain pathogens, even in locations far from a laboratory.

At the same time, we are working on improved LiDAR systems. ‘LiDAR’ stands for Light Detection and Ranging, a laser-based distance measurement technology. Polariton filters can help to expand the field of view of these types of systems. As a result, an autonomous vehicle or industrial robot would require fewer LiDAR scanners to reliably monitor its entire surroundings. This reduces both the costs and energy consumption of such systems, making a significant contribution to productivity and safety.