Manipulating laser light with perovskites

Australian researchers have found a way to manipulate laser light at a fraction of the cost of current technology — a breakthrough that could help drive down costs in industries such as telecommunications, medical diagnostics and consumer optoelectronics.

Led by Dr Girish Lakhwani from the University of Sydney Nano Institute, the research team used inexpensive crystals, known as perovskites, to make Faraday rotators. These manipulate light in a range of devices by altering its polarisation, giving scientists and engineers the ability to stabilise, block or steer light on demand.

Faraday rotators are used at the source of broadband and other communication technologies, blocking reflected light that would otherwise destabilise lasers and amplifiers. They are used in optical switches and fibre-optic sensors as well.

“The global optical switches market alone is worth more than US$4.5 billion and is growing,” Dr Lakhwani said. “The major competitive advantage perovskites have over current Faraday isolators is the low cost of material and ease of processing that would allow for scalability.”

To date, the industry standard for Faraday rotators has been terbium-based garnets. Dr Lakhwani and colleagues at the ARC Centre of Excellence in Exciton Science (ACEx) have used lead-halide perovskites, which could prove a less expensive alternative. This class of materials has been gaining a lot of traction in the scientific community, due to a combination of good optical properties and low production costs.

“Interest in perovskites really started with solar cells,” said Dr Randy Sabatini, a postdoctoral researcher leading the project in the Lakhwani group.

“They are efficient and much less expensive than traditional silicon cells, which are made using a costly process known as the Czochralski or Cz method. Now we’re looking at another application, Faraday rotation, where the commercial standards are also made using the Cz method. Just like in solar cells, it seems like perovskites might be able to compete here as well.”

The team showed that the performance of perovskites can rival that of commercial standards for certain colours within the visible spectrum, publishing their results in the journal Advanced Science. Dr Lakhwani noted, “It’s very difficult to find solution-processed materials that rotate light polarisation effectively. Based on their structure, we were hoping that perovskites would be good, but they really surpassed our expectations.”

Looking ahead, the search for other perovskite materials should be aided by modelling.

“For most materials, the classical theory used to predict Faraday rotation performs very poorly,” said Dr Stefano Bernardi, a postdoctoral researcher at the University of Sydney. “However, for perovskites the agreement is surprisingly good, so we hope that this will allow us to create even better crystals.”

The team has also performed thermal simulations to understand how a real device would function. However, there is still work to be done to make commercial application a reality.

“We plan on continuing to improve the crystal transparency and growth reproducibility,” said Chwenhaw Liao, from UNSW. “However, we’re very happy with the initial progress and are optimistic for the future.”

Image caption: Schematic of Faraday rotation. Polarisation of incoming light is rotated by the medium within a magnetic field. Image courtesy of the study authors under CC BY 4.0.

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