Light Powers Micromachines

Richard Gaughan

Machines based on microelectromechanical systems (MEMS) and micro-optoelectromechanical systems show promise for innumerable applications.

Some macroscopic structures can be scaled to microscopic dimensions; however, the relative magnitude of the physical forces acting on them changes significantly with scale, so innovative methods of driving motion are necessary to operate MEMS-based machines. One is photon pressure.

Professor Robert C. Gauthier and his colleagues at Laurentian University and at Carleton University in Ottawa had modeled the motion of gearlike structures under the influence of laser radiation and got encouraging results. After completing the initial experimental work of suspending and rotating unattached gears above the substrate from which they were manufactured, the researchers moved on to experimenting with gears on capped posts. To maximize torque and minimize binding to the post, the laser light was incident at 10° above the plane of the gear.

The team had determined that a laser beam should be able to keep a nine-armed gear in continuous motion. To verify the model, the group photolithographically manufactured 65-µm-diameter, 2-µm-thick gears from polysilicon and coated them with aluminum and titanium. A 785-nm, 70-mW laser diode was focused to an 8-µm-diameter spot 25 µm out along the gear arm. A CCD imaging system recorded the rotation.

Stay cool

When the gears rotated in air, thermal effects disrupted their motion and caused damage to the structures. In water, however, the gears exhibited a rotation rate that was linearly proportional to the applied force.

Now that they have demonstrated the viability of motivating MEMS machines with light pressure, the researchers, who reported their work in the Feb. 20 issue of Applied Optics, will attempt to integrate the optics in a MEMS device and to optimize the optomechanical efficiency. If they are successful, they will have developed an all-dielectric, small-footprint system that is suitable for use in harsh environments and that is compatible with electronics and semiconductors.