A transparent microactuator from a single piece of glass

The allure of combining optics and mechanics is strong, with applications in displays, adaptive optics, and many other technologies. As the devices continue to shrink, their fabrication becomes ever more complicated. Working at Eindhoven University of Technology in the Netherlands, Yves Bellouard and Bo Lenssen have developed a relatively simple method to manufacture a complex actuator out of a single glass substrate. First they use low-power femtosecond pulses, applied in a predetermined pattern, to selectively and simultaneously change both the glass's refractive index and its susceptibility to chemical etching. And because the transparent material is affected only at the focal point and only when the laser exceeds a certain power threshold, regions below the glass surface can be altered with pinpoint accuracy. Next, they etch the device in a chemical bath, which erodes the glass an order of magnitude faster in the laser-painted regions. Finally, when the sculpture is complete, a transparent coating of indium tin oxide is deposited to form electrodes and capacitors. How does the device work? As seen in the image, the teeth of two combs interleave. Each pair of parallel prongs forms a capacitor and, with a suitable voltage applied and only one comb free to move, an electrostatic force induces the smaller gaps between the combs to further shrink, producing useful motion (a video is available). Being transparent, the Eindhoven actuator could be useful in microscopy, adaptive optics, interferometry, or even tunable resonant optical cavities. (B. Lenssen, Y. Bellouard, Appl. Phys. Lett. 101, 103503, 2012.)—Stephen G. Benka