Ultra thin two-dimensional materials can rotate the polarization of visible light

For centuries, people have known that light exhibits wave like behavior in certain situations. When light passes through certain materials, they can change the polarization of light waves (i.e. the direction of oscillation). The core components of optical communication networks, such as optical isolators or photodiodes, utilize this characteristic. This type of component allows light to propagate in one direction but blocks all light in the other direction.

In a recent study, physicists from Germany and India showed that ultra-thin two-dimensional materials such as tungsten selenide can rotate the polarization of visible light at certain wavelengths by several degrees under a small magnetic field suitable for chip use. Scientists from the University of M ü nster in Germany and IISER in Pune, India, published their research findings in the journal Nature Communications.

One of the problems with traditional optical isolators is their considerable volume, ranging in size from a few millimeters to a few centimeters. Therefore, researchers are still unable to manufacture micro integrated optical systems on chips that can compete with everyday silicon-based electronic technology. Currently, there are only a few hundred components on integrated optical chips.

Faraday effect in two-dimensional semiconductors
By contrast, computer processor chips contain billions of switching elements. Therefore, the research work of the German and Indian teams has taken a step forward in the development of miniature optical isolators. The two-dimensional materials used by the researchers are only a few atomic layers thick, making them 100000 times thinner than human hair.

Professor Rudolf Bratschitsch from the University of Minster said, "In the future, two-dimensional materials may become the core of optical isolators and enable on-chip integration of current and future quantum optical computing and communication technologies."
Professor Ashish Arora from IISER added, "Even the bulky magnets required for optical isolators can be replaced by atomic level thin two-dimensional magnets. This will greatly reduce the size of photonic integrated circuits."

The research team deciphered the mechanism that led to their discovery: bound electron hole pairs, also known as excitons, in two-dimensional semiconductors cause strong polarization rotation of light when ultra-thin materials are placed in a small magnetic field.
Arora said, "Conducting such sensitive experiments on two-dimensional materials is not easy because the sample area is very small. Scientists had to develop a new measurement technique that is about 1000 times faster than previous methods."

Source: Physicist Organization Network