A light beam passing through a piece of glass usually just bends slightly. But if you engrave ultra-fine patterns inside the glass with a laser, you can make the light split into separate beams, much like white light fans out into a rainbow after rain. That's exactly what the authors set out to do: they created a miniature light transformer the size of a grain of salt, just a third of a millimeter long.
Inside a glass plate, a laser drew several layers of microscopic grooves. Each layer acts like a hologram that twists the light wave in its own way. When a laser beam with circular polarization passes through these layers, it gradually changes shape. At the output, you get several distinct beams, each carrying away its share of energy. This way, they managed to separate 28 overlapping light modes that, without such a device, would look like a single blurry spot.
These glass chips can do more than sort light. If you send a beam with a specific structure through them, the output is the result of a mathematical operation — say, matrix multiplication. Light passing through random patterns performs calculations on its own, with no electronics involved. This approach echoes the analog computers of the past, but it works at the speed of light.
The technology bridges two worlds: free-space light propagation and integrated circuits, where everything is packed into a tiny volume. In the future, such transformers could become the foundation for compact optical communication devices and photonic computing.
To create the grooves inside the glass, the laser fires pulses lasting quadrillionths of a second — in that time, light travels a distance shorter than the thickness of a human hair.
In the series 'The Expanse,' ships communicate via laser beams that encode information in the structure of light — similar transformers could separate such signals.