Technology forum – laser – photonics

On-chip integration of optical isolators

Conventional optical isolators are relatively large, with dimensions ranging from millimetres to centimetres. As a result, it has not yet been possible to create miniaturised integrated optical systems on a chip that are comparable to everyday silicon-based electronic technologies. In a recent study, German and Indian physicists from the University of Münster and the Indian Institute of Science Education and Research (IISER) in Pune, India, show that ultra-thin, two-dimensional materials such as tungsten diselenide can rotate the polarisation of visible light by several degrees at certain wavelengths under small magnetic fields suitable for use on chips.

Two-dimensional semiconductor rotates light

The 2D materials used by the researchers should only be a few atomic layers thick. “In the future, two-dimensional materials could become the centrepiece of optical isolators and enable on-chip integration for current optical and future quantum optical computer and communication technologies,” says Prof. Dr Rudolf Bratschitsch from the University of Münster. “Even the relatively bulky magnets, which are also required for optical isolators, could be replaced by atomically thin 2D magnets,” adds Prof Dr Ashish Arora from IISER. This would drastically reduce the size of photonic integrated circuits.
The team deciphered the mechanism responsible for the effect they found: Bound electron-hole pairs, so-called excitons, in 2D semiconductors rotate the polarisation of the light very strongly when the ultra-thin material is placed in a small magnetic field. “Conducting such sensitive experiments on two-dimensional materials is not easy, as the sample areas are very small,” emphasises Arora. According to the scientists, they had to develop a new measurement technique that is around 1000 times faster than previous methods.

The German Research Foundation (DFG), the Alexander von Humboldt Foundation, the Indian technology foundation I-Hub, the Science and Engineering Research Board (SERB) of the Indian Ministry of Technology and the Indian Ministry of Education supported the work financially.

Original publication

[Carey, B., Wessling, N.K., Steeger, P. et al. (2024): Giant Faraday rotation in atomically thin semiconductors. Nat. Commun. 15, 3082. DOI: 10.1038/s41467-024-47294-5]



Image: Nature Communications (Nat Commun) ISSN 2041-1723 (online); Creative Commons licence