Researchers from the Institute of Complex Systems of the National Research Council in Rome (CNR-Isc) and the Department of Physics of Sapienza University of Rome have developed an innovative instrument that allows researchers to 'see' through polarisation and use this property for applications in the fields of secure optical communication over long distances, photonic sensors with increased functionality, and new instruments for medicine.

Polarisation, along with frequency and intensity, is one of the three fundamental properties of electromagnetic waves. While the latter two are manifested daily through the colours and brilliance of many different light sources such as LEDs, microwaves and lasers, the polarisation of light is less well known. Our eyes are not sensitive to this property - which indicates the direction of oscillation of the optical field - and we, therefore, do not realise how it underlies the functioning of everyday objects such as displays.

Seeing through polarisation makes it possible to detect seemingly invisible objects in very poor visibility and discover details hidden in ordinary photographs. In addition, in applications such as digital vision, it makes it possible to observe hidden physical characteristics of materials - such as tensions, torsions and surface imperfections - and plays a key role in quantum information.

The instrument developed by Davide Pierangeli and Claudio Conti of the CNR's Institute of Complex Systems and Sapienza's Department of Physics, overcomes the lack, until now, of compact methods and instruments for obtaining ultra-fast polarisation images: current detectors - so-called polarimeters - use many measurements through expensive and voluminous optical apparatuses.

In particular, the device is innovative because it allows many polarisations to be measured in a single 'shot', relying on artificial intelligence. Moreover, it does not require conventional optical polarisation components.

"Revealing the so-called 'third dimension of light' efficiently is a central challenge for photonics," says Davide Pierangeli (CNR-Isc). "Our idea was to reveal polarisation by measuring another physical property apparently unrelated to it, i.e. the optical intensity distribution produced by a disordered chip. From this, via machine learning techniques, extract information about the many polarisations encoded in the laser beam."

"Our study demonstrates an artificial intelligence-based smart polarisation detector with functionality currently unobtainable in conventional instruments," says Claudio Conti (Sapienza University of Rome). "This paves the way for secure optical communication, new tools for medicine and autonomous driving."

The result, published in Nature Communications, opens up important perspectives for applying structured polarised light in optical communication, imaging, and computation

References: 

Single-shot polarimetry of vector beams by supervised learning - Davide Pierangeli & Claudio Conti - Nature Communications (2023) https://doi.org/10.1038/s41467-023-37474-0

Further Information 

Claudio Conti
Department of Physics
claudio.conti@uniroma1.it