A chip that steers light with light, in 74 femtoseconds

Most ways of pointing a laser beam somewhere else are slow. You can move a mirror, but that's mechanical and takes milliseconds. Or you can push charge around inside a material, which is faster, but you still have to wait for those charges to settle down. A group at Caltech just published a way around both, and I think it's worth knowing about.

They took a thin film of amorphous silicon and patterned it into a surface covered in tiny pillars. Each pillar is smaller than the wavelength of the light hitting it. The sizes and spacing are chosen so the light doesn't just pass straight through. It hangs around for a moment and recirculates. That extra dwell time is the whole trick. Silicon's refractive index changes very slightly when a strong light pulse hits it, and normally that change is far too weak to do anything useful. Making the light linger amplifies the effect enough to actually bend a second beam.

The result: they steered beams by up to 13 degrees, and the switch happened in 74 femtoseconds. No moving parts anywhere. One pulse of light steering another.

The detail I like most is that 74 femtoseconds was also the length of the pump pulse they used. So the material wasn't the thing holding them back. Their laser was. Use shorter pulses and it should go faster still.

This is lab work, not a product, and I have no idea how long it takes to become one. But fast beam steering without moving parts is a limit that optical computing, sensing and communications keep running into. The paper is in Nature Nanotechnology.

Source: https://www.sciencedaily.com/releases/2026/09/260918024823.htm