How do you trap light inside something that’s filled with holes? That may sound like an odd question, but it’s one that researchers have been grappling with to create a new kind of microscopic container that locks light in but lets fluids pass straight through.

Light has a habit of finding its way through the tiniest of holes; the small gap between your curtains, for instance, but far smaller holes, too. If you want to seal light off entirely, then, you need to fill each and every gap—which is fine, unless you need to access what’s on the other side.

But a team of researchers from the Australian National University in Canberra have been playing around with something they call optical metacages. As New Scientist reports, these (currently conceptual) cages can be built up using nanowires as bars. These wires absorb and reflect light in strange ways, and the team’s models show that 200-nanometer wire can actually absorb light from up to 100 nanometres from their outside surface


That means that, when the wires are neatly spaced out like a picket fence, gaps allow fluids through, while light remains tightly penned into a well-defined space. The example above shows a simple silhouette of Australia trapping light. The research is to be published in Physical Review Letters.

Of course, this is all theoretical—the team now need to actually make the things. But if they can do that, the cages could be used to shield living cells from electromagnetic radiation while still being supplied with fluids and nutrients.

[Physical Review Letters via New Scientist]