For over 30 years, scientists have worked to make gears smaller for building micro-engines. However, they could not go below 0.1 millimeters because traditional drive trains, the systems that connect and move gears, were too hard to build at that scale. Researchers from Gothenburg University have now solved this problem by replacing mechanical drive trains with laser light to directly spin the gears.
The researchers use optical metamaterials that capture and control light on a nanoscale, meaning at sizes of billionths of a meter. These gears are made from silicon on a microchip using lithography. Each gear has a diameter of just a few tens of micrometres. When a laser shines on the metamaterial, it causes the gear to spin. The laser's intensity, or strength, controls the speed, and changing the light's polarization reverses the gear's rotation. This approach brings them close to creating micromotors, small rotating devices.
A shift to light-driven systems
The researchers have also created a gear train, a series of connected gears, where one light-driven gear starts the whole chain moving. These gears can change spinning motion into straight-line movement, create repeating patterns of motion, and adjust tiny mirrors to redirect light. Because the system fits directly on a chip and uses light without needing physical connections, it can grow into complex microsystems, or miniature integrated setups. This new approach to microscale mechanics avoids the bulk of traditional parts and breaks the old size limits.
Looking ahead, these advances could lead to micro- and nanomachines, devices at even tinier scales, that handle light, move small particles, or fit into lab-on-a-chip systems, portable tools for quick tests. Gears can be as small as 16 to 20 micrometres, matching the size of some human cells. In medicine, they might act as pumps inside the body to control flows or as valves that open and close.
This research is published in Nature Communications.