Because it’s built on silicon technology its manufacture can be scaled, with the potential to push costs down below $1 per filter, its developers said. The research has been published in Laser and Photonics Reviews.

Spectroscopy relies on spreading the light source into a spectrum, which is conventionally done with a grating or prism to spread the infrared light: different parts of the spectrum are sent into the sample by tilting the grating back and forth.

For robustness, the Transformative Meta-Optics team at the ARC Centre of Excellence instead opted for a non-moving component to select specific parts of the infrared spectrum, in the form of a band-pass filter. Drawing on other research within TMOS that had used heating to vary component behaviour, they devised a filter with temperature-dependent band-pass wavelength.

“The great thing about it is that it is very stable and reversible,” said Ben Russell, PhD student in TMOS. He then created prototypes of both by carefully etching the pattern into an off-the-shelf silicon-on-sapphire wafer – which needed a few repeats, as he initially underestimated the etching rate.

Sure enough, the finished prototype behaved as modelled, displaying a linear wavelength shift of 80 nanometers, across the standard operating temperatures from 25 Celsius to 420 Celsius. More extreme heating and cooling to cryogenic temperatures extended this to 140 nanometres– although these extremes are unlikely to be of practical use in the future.

With stable temperature tuning achieved, the team tested the spectroscopic capabilities of the filter on a number of everyday items, for example successfully measuring polymide tape and a zinc selenide window. They were also pleased to be able to easily distinguish between two clear, recyclable plastics of different composition, LDPE and PET.