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20.12.2022 17:55

Terahertz Radiation: Scientist at TU Berlin Works on a Chip for the Blind Spot in the Electromagnetic Spectrum

Stefanie Terp Stabsstelle Kommunikation, Events und Alumni
Technische Universität Berlin

Maurizio Burla is a new professor at TU Berlin and brings with him an ERC grant. With it, he wants to build a chip with an optical core that can receive, process and transmit terahertz radiation for the first time – with applications in medicine and 6G mobile communications

There is a gap between radio waves and microwaves on the one side of the electromagnetic spectrum and infrared and light rays on the other: terahertz radiation. Unlike electromagnetic waves with smaller or larger frequencies, there is no chip technology that can process the radiation efficiently and thus cost-effectively. However, this would be important, as terahertz radiation forms the basis for the next mobile phone generation 6G, for new imaging processing in medicine as well as for new types of sensors. Last but not least, the terahertz spectrum in astronomy offers the possibility of detecting atoms and molecules in space. Prof. Dr.-Ing. Maurizio Burla, the new head of the Chair of High-Frequency Technology Photonics at Technische Universität Berlin, is now working on a terahertz chip technology based on a symbiosis of electrical and light-conducting components. He is financially supported by a Starting Grant of 1.89 million euros from the European Research Council (ERC).

Terahertz beams became known primarily through the body scanners that are now available in some airports at security checks as an alternative to manually scanning travelers. In medicine, for example, the beams could detect the healing of complicated burns under the dressing without having to change it frequently and damaging the tissue in the process. Terahertz radiation would also make it easier to distinguish tumors from healthy tissue during surgery or early cancer detection [1]. "However, such applications require a much higher resolution than body scanners," explains Maurizio Burla. In addition, a compact and cost-effective design is crucial for good manageability and widespread use, he adds.

New mobile phone generation 6G is based on terahertz beams
“The same is especially true for the application of terahertz beams for mobile radio”, says Burla. The new 6G mobile radio generation will be based on terahertz or sub-terahertz beams in the range of 100 to 300 gigahertz. Due to the high-frequency values, there is a large span of individual frequencies that can be used in this range. With this large “bandwidth”, hundreds of gigabit per second could be sent – transmitting the information over many frequencies. In addition, the large frequency span makes it possible to integrate many providers and different applications in the system.

The waves must be tamed
However, it is a law of physics that high-frequency waves, which frequently change between their crests and troughs, are weakened during transmission much more than lower frequency ones, and this brings the need to focus the waves more strongly on their targets. "This means that the antennas have to transmit in a targeted manner and track when objects are moving. The correct amplification of weak input signals also takes on special significance here," Burla points out. "All this requires integrated, analog processing of terahertz waves. This is exactly what our new chip is designed to do."

Analog and digital electronics reach their limits
However, this brings forth great difficulties with the components available today: In electronics, the amplification effect of transistors drops to almost zero with increasing frequency. Also, simple electrical resistors suddenly act as capacitors at high frequencies, which drastically increases the energy loss of incoming signals from antennas. "Analog electronics simply start to approach their physical limits at these high frequencies," says Maurizio Burla. "Unfortunately, so does digital electronics, for practically the same reasons. Converting terahertz waves into zeros and ones and then processing the signals digitally, is very difficult due to the limited speed and high power consumption of the converters as frequencies become too high." All this results in an extremely limited capability to process waves at those high frequencies.

Photonics chip as a solution
Maurizio Burla sees the solution to these problems in a technology that was actually developed for much higher frequencies – photonics. Here, tiny, micro- and nanometer-sized structures in semiconductors or glasses conduct light waves that usually come from lasers. In this way, they can be amplified – similar to the current in electronics – and flexibly processed in logic circuits. Burla now wants to “modulate” the laser beams with the terahertz signals in order to be able to process these modulations with the help of the established photonic elements. “But this requires very special modulators and transducers," he explains “which need to be about a factor of ten faster than what is on the market today.”

The trick with modulation
In Burla’s concept, e.g. an antenna captures terahertz waves and directs them to a transducer. A laser beam also passes through the transducer. The terahertz waves influence the laser waves in the transducer. Depending on the properties of the terahertz waves, the laser waves also change their properties. This can refer to the height of the wave crests, their distances or also to the shifting of individual wave trains against each other. The important thing is that these changes in the laser waves occur more or less in time with the terahertz waves - they are "modulated" by them. Special crystals or resonance “chambers”, for example, in which the two types of waves can interact with each other, can be used as transducers if carefully engineered.

Considerable development work is necessary
"Through modulation, we can now process all the information from the terahertz waves – with the help of the laser beams – in the known photonic components," says Burla. This is a great advantage, because photonics already uses highly integrated, i.e. very compact, designs. Nevertheless, there is still a lot of development work to be done, Burla emphasises. For example, due to the large bandwidth of terahertz waves, the converters would have to work uniformly (linearly) over a very large frequency range. They also should convert the properties of the terahertz waves exactly, without “clipping” and, at the same time, without adding too much noise. "The information processing of a terahertz modulated signals also places extreme demands on the quality of the photonic components,” says Maurizio Burla. “They also need to be specially designed to be so fast to be able to tackle terahertz signals.”

Ideal research environment in Berlin
Through his research at the University of Twente in the Netherlands, the University of Québec in Canada and ETH Zurich, Burla is very familiar with the world of microwave and terahertz radiation as well as with classical photonics. In addition, he benefits from the scientific environment at TU Berlin, building connections with other chairs having synergetic expertise in communication theory, integrated circuit design, microwave and radio frequency engineering – to name just a few. The spatial proximity to the Fraunhofer Institutes HHI and IZM in Berlin and the Leibniz Institute for Innovative Microelectronics (IHP) in Frankfurt/Oder is also a great location advantage, says Burla. As the successor to Prof. Dr.-Ing. Klaus Petermann, he also benefits from the existing cleanroom and technical infrastructure which he is now further enhancing to match what is needed for this novel research. Maurizio Burla is therefore confident that he will be able to present the first demonstration chip for terahertz beams at the end of the five-year project period of his ERC Starting Grant in 2027.

Further information:

Link to the ERC Starting Grant of Prof. Dr. Maurizio Burla:

https://cordis.europa.eu/project/id/948624

Cited sources:

[1] https://www.empa.ch/de/web/s604/terahertz-eq66

For further information please contact:

Prof. Dr.-Ing. Maurizio Burla
Technische Universität Berlin
Chair of High-Frequency Technology Phonetics
Tel.: +49 (30) 314-70823
Email: burla@tu-berlin.de

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