Infrared signals from distant stars that formed soon after the Universe itself could one day be discerned from Earth, thanks to a specially designed filter. Such signals are normally drowned out by a blaze of infrared emissions of wavelength 1,000–1,800 nanometres coming from hydroxyl chemicals in Earth's upper atmosphere.

The filter, developed by Joss Bland-Hawthorn at the University of Sydney, Australia, and his colleagues, combines two technologies: Bragg gratings, which are fibre-optic cables with unevenly spaced notches that suppress and reflect up to 400 hydroxyl spectral lines; and a converter that funnels the light from the sky into the grating as a single ray.

Tests at an observatory over three evenings showed that the filter blocked out most of the brightest emissions with wavelengths between 1,440 and 1,630 nanometres. Although a still a prototype, the device could be used with 8-metre and future 30-metre telescopes, the authors say.

Nature Commun. 2, 581 (2011)