High-precision, ultra-fast and energy-efficient information processing is required in many applications, whether in communication systems, the use of artificial intelligence or when working with precision measuring devices. The German Research Foundation (DFG) has now extended funding for the "MINTS" (MLL-based Integrated THz Frequency Synthesiser) project for a further three years with a funding sum of around 415,000 euros. In collaboration with the Fraunhofer Heinrich Hertz Institute (HHI) in Berlin, the project team led by Prof Dr Christoph Scheytt from the Institute of Electrical Engineering and Information Technology and head of the "Circuit Technology" department at the Heinz Nixdorf Institute at Paderborn University and Prof Dr Martin Schell, head of the Fraunhofer HHI, is researching and developing synthesizers that can generate very precise and stable frequencies in the terahertz (THz) range. To put this into perspective, these frequencies lie between infrared light and microwaves.
Efficient systems with low phase noise
Since the beginning of 2022, the scientists in the "MINTS" project have been investigating electronic-photonic THz frequency synthesiser architectures. A THz frequency synthesiser is essentially a device that is capable of generating very precise and controllable signals at very high frequencies. "For a long time, a major challenge was that there were no effective technologies that worked efficiently between the infrared and microwave ranges. However, with advances in semiconductor and laser technology, THz technology has become much more accessible, explains Scheytt. For example, THz radiation can be used for imaging processes, such as in spectroscopy, for materials research, in security technology and in wireless communication with very high data rates.
The scientists are not only focussing on generating high frequencies, but are also working on stability, precision and controllability. A key challenge is phase noise, which affects signals in both electronic and optical devices and leads to rapid fluctuations in the signal. "This can weaken signals or lead to faulty data transmission in communication systems," explains project partner Schell. "Our aim is to achieve lower phase noise than with purely electronic THz frequency synthesisers and thus ensure maximum signal stability," adds Scheytt. Reducing susceptibility to phase noise improves signal quality and allows systems to operate more efficiently, resulting in lower energy consumption and sponsors the development of more sustainable technologies.
Initial successes and plans for the second project phase
In the first phase of the project, the scientists succeeded in accurately modelling the electro-optical phase detector, the core circuit of the OEPLL synthesizer, characterising the additive phase noise in silicon photonic waveguides and drive amplifiers, and measuring the phase noise of THz signals. Silicon waveguides are fundamental to silicon photonics and play a central role in optical signal transmission and processing on a microchip. The researchers use an electro-optical phase detector to measure the phase shift between an electrical and an optical signal. This device is used in various technical and scientific applications, for example in communication technology, where optical data transmission systems need to be calibrated and monitored to ensure stable operation.
In the second phase of the project, the team will build on the success of the first phase and work on further optimisations. "We are investigating an alternative discrete approach to generate THz signals from MLL while pursuing the hybrid integration of THz-OEPLL using a silicon photonics (SiPh) or indium phosphide (InP) PIC chip and a SiGe THz emitter chip to enable a miniaturised THz source," says Vijayalakshmi Surendranath Shroff, research associate at the Heinz Nixdorf Institute. These technologies are used, for example, in modern data centres, lidar systems, quantum computers and high-speed telecommunications.
