Light moves tiny devices

02 Dec 2008

All-optical mechanical devices could be a step closer thanks to researchers in the US who are using light to drive nanoscale mechanical devices.

Engineers at Yale University have shown that the force of light can be harnessed to drive nanomachines. The result could lead to all-optical mechanical devices made from nanometre-sized photonic circuits (Nature 456 480).

The work successfully combines two important emerging fields of research, nanophotonics and nanomechanics, and could make it possible to create tiny optical and mechanical components on the same silicon chip.

Although the force exerted by photons is too weak to be felt in everyday life, it can be greatly enhanced by concentrating light in nanosized photonic circuits.

Until know, the force of light has only been used to move small objects in a technique called "optical tweezers". They work by trapping micrometre-sized objects near the focus of a laser beam. The technique allows objects to be picked up and moved to another place using just light. Now, Hong Tang and colleagues have taken this concept a step further and have shown that optical forces can be exploited to move an entire semiconductor device.

The researchers showed that, when they passed concentrated light through a free-standing nanomechanical photonic resonator, which also acts as a waveguide for light, the resonator bends. The optical force causing this displacement can be measured as a change in the coupling between the resonator and an underlying substrate. The force (which can be as high as 8 pN per micron per milliwatt) would be large enough to move nanoscale machinery on a chip, say Tang and colleagues.

The optical force produced in the new method actually acts perpendicular to the direction of the light beam. This is in contrast to previous systems where the optical force was parallel to the direction of light propagation. This now means that mirrors or cavity configurations, which are difficult to implement in integrated chip-scale systems, are no longer required. And that's not all: the light force is intrinsically fast and can thus drive nanomechanical devices at very high frequencies, possibly surpassing the current milestone of a few gigahertz, said Tang.

He explained that the magnitude of the force is about the same size as other forces commonly used to actuate nanodevices, such as electrostatic and magnetic forces, but no external fields are needed. "All this implies that it will be possible to develop a complete photonic nanoelectromechanical system with integrated optical sensing and actuation in the near future."

All optical devices would also require much less power than devices that use electrons.