High-Speed Material Properties for Tomorrow's Digital Infrastructure Uncovered

A team of researchers from the Institute of Electromagnetic Fields (IEF) at ETH Zurich has addressed a critical knowledge gap in photonic integrated circuit development in the most recent issue of Nature Materials. The study, entitled "Barium titanate and lithium niobate permittivity and Pockels coefficients from megahertz to sub-terahertz frequencies," provides the first comprehensive characterization of two essential materials used in photonic integrated circuits across the yet largest frequency range.

The research focuses on the key materials lithium niobate (LN) and barium titanate (BTO) which exhibit the Pockels effect. This Pockels effect allows to tune the refractive index of an optical material by means of an electrical signal. It is essential to encode electrical information onto an optical laser signal. The effect is widely used in photonic circuits such as used in fiber communications where light rather than electricity carries digital information.

"Our work represents the first comprehensive characterization of these materials across such a wide frequency spectrum," says Dr. Daniel Chelladurai, the study's lead author. "We were particularly surprised by BTO's strong frequency dependence, which contrasts sharply with the stable response observed in lithium niobate. Despite this variation, we demonstrated that BTO offers remarkable electro-optic performance up to the highest frequencies."

To extract the material properties the researchers introduced new waveguides structures along with a measurement technique that allowed them to directly characterize the material properties in actual devices. This approach provides unprecedented insight into material behaviour under real operating conditions.

Professor Juerg Leuthold, who leads the research group at IEF, emphasized the broader implications: "Photonic integrated circuits represent the next frontier in information processing technology. By understanding how these materials behave across such a wide frequency range, we've created a foundation for designing devices that can operate at speeds previously considered challenging. Our measurement approach also provides a standardized method for evaluating new materials that are about to emerge."

The implications of this work extend to numerous emerging technologies, including:
• High-speed optical communications beyond 100 GHz
• Quantum networks requiring efficient microwave-to-optical conversion
• Programmable photonic circuits
• Reconfigurable metasurfaces for augmented and virtual reality

The research establishes both a comprehensive data set for current materials and a methodological framework for characterizing future electro-optic materials. The team at IEF hopes the work will accelerate the development of next-generation photonic integrated circuits that can operate at unprecedented speeds.

For more information, please refer to the complete article in Nature Materials external page here.