Engineered nanostructure transforms polarisation state of light

A single layer of metallic nanostructures has been designed, fabricated and tested by a team of Penn State University electrical engineers that can provide exceptional capabilities for manipulating light. 

It is claimed that the engineered surface, which consists of a periodic array of strongly coupled nanorod resonators, could improve systems that perform optical characterisation in scientific devices, such as ellipsometers; sensing, such as biosensing of proteins; or satellite communications.

‘We have designed and fabricated a waveplate that can transform the polarisation state of light,’ said Zhi Hao Jiang, a postdoctoral fellow in electrical engineering and lead author of a paper describing the research in Scientific Reports. ‘Polarisation is one of the most fundamental properties of light. For instance, if we transform linearly polarised light into circularly polarised light, this could be useful in optical communication and biosensing.’

According to the Pennsylvanian university, optical waveplates with broadband polarisation conversion over a wide field of view are highly sought after. Conventional waveplates have difficulty achieving broadband and wide-angle conversion. Thin waveplates have been demonstrated, but their efficiency was low, with an average power efficiency of less than 50 per cent.

The Penn team’s nanofabricated waveplates are said to have achieved measured polarisation conversion rates higher than 92 per cent over more than an octave bandwidth with a wide field-of-view of around 40 degrees.

‘In this paper, we demonstrated with simulation and experiment both quarter-waveplate and half-waveplate metasurfaces, which are thin artificial surfaces that operate both in the visible spectrum as well as in the near infrared,’ said team member Jeremy Bossard in a statement. ‘It also has a wide field of view, which means that if you illuminate the surface from a wide range of angles, it would still give the same reflective performance.’

As a component in an optical setup, the nanostructured waveplate is claimed to offer a thinner form factor and reduced weight for space applications, a wider field of view, which can reduce the number of optical components in a system, and can achieve very wide broadband functionality in the visible to near infrared wavelength range.

This represents a new advance for optical meta-surface based devices and will enable other types of ultrathin highly efficient optical components, the authors said.

The paper published in Scientific Reports is titled ‘Broadband and Wide field-of-view Plasmonic Metasurface-enabled Waveplates.’ The work was supported by the US National Science Foundation through Penn State’s Center for Nanoscale Science.