E-Paper
One-molecule-thick 2D semi-conductors can rotate polarised light very strongly: Study
Dr. Ashish Arora and team discovered that ultra-thin two-dimensional semiconductors can strongly rotate polarized light, promising applications in optical computation and quantum technologies. Reported in 'Nature Communications', the study shows potential for miniaturized integrated optical systems on chips.
Dr Ashish Arora from the Indian Institute of Science Education and Research (IISER) Pune, India and professor Rudolf Bratschitsch and team from the University of Munster, Germany, in collaboration, have discovered that one-molecule-thick ‘two-dimensional semi-conductors’ can rotate polarised light very strongly, thus opening up the potential for applications in integrated optical computation and quantum technologies. The work has been reported in the journal, ‘Nature Communications’. The study has shown 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 in chips.
Arora from IISER Pune, who is one of the two lead authors of the study, said, “These materials are only one molecule thick, which is a hundred thousand times thinner than a human hair; nothing can go thinner than this. It is surprising that this Faraday rotation is so large. We used a property of these materials that at certain wavelengths, something known as an exciton can be created in the material. This exciton rotates the plane of polarisation very strongly when the material is placed under a magnetic field.”
“One of the problems with conventional optical isolators is that they are quite large, with sizes ranging between several millimetres and several centimetres. As a result, researchers have not yet been able to create miniaturised integrated optical systems on a chip that are comparable to everyday silicon-based electronic technologies. Current integrated optical chips consist of only a few hundred elements on a chip,” Arora said.
Professor Bratschitsch from the University of Münster, the other lead author of the work, said, “In the future, two-dimensional materials could become the core of optical isolators and enable on-chip integration for today’s optical and future quantum optical computing and communication technologies.”
“Performing such sensitive experiments on two-dimensional materials is not easy since the sample areas are very small. We had to create a new method to measure Faraday rotation which is about 1,000 times faster than the previous technique,” said Bratschitsch.
In comparison, a computer processor chip contains many billions of switching elements. The work of the team is, therefore, a step forward in the development of miniaturised optical isolators. The 2D materials used by the researchers are only a few atomic layers thick and therefore a hundred thousand times thinner than a human hair. The work is funded by the I-Hub Technology Foundation and SERB of the Department of Technology of India, and the Ministry of Education of India, the German Research Foundation, the Alexander Von Humboldt Foundation of Germany.
It has been known for centuries that light exhibits wave-like behaviour in certain situations. Some materials are able to rotate the polarisation namely the direction of oscillation, of the light wave when light passes through the material. This property is utilised in a central component of optical communication networks known as an ‘optical isolator’ or ‘optical diode’. This component allows light to propagate in one direction but blocks all light in the other direction.
