An ordinary lens always refracts light the same way. Its properties are frozen in glass forever. But now there's a surface that changes the game on the fly.
Scientists made an ultrathin film with resonant elements and infused it with liquid crystals — the same stuff used in phone screens. When light hits this film, it generates a triple frequency (known as third-harmonic generation). But the key is that another beam of light can rotate the liquid crystal molecules like clock hands. The rotation changes how strongly the light is converted and in which direction it goes.
This trick allows changing the nonlinear response in real time, as if you could switch the signal processing formula without changing the circuit itself. Previously, you'd have to fabricate a new device.
This is a step toward photonic computers, where light does the computing instead of electrons. And now these circuits can be reprogrammed like a regular processor.
In displays, liquid crystals rotate under an electric field, but here they are rotated by light itself — no wires or contacts.
In the novel "Light of Distant Stars," photonic circuits reconfigured on the fly to suit the crew's needs: it seems science fiction is getting closer.