By 'putting a ring on it,' microparticles can be captured

Jul 20, 2010
This is a schematic illustration of a particle revolving around a silicon micro-ring resonator, propelled by optical forces. Credit: Courtesy of Ken Crozier, Harvard School of Engineering and Applied Sciences.

To trap and hold tiny microparticles, engineers at Harvard have "put a ring on it," using a silicon-based circular resonator to confine particles stably for up to several minutes.

The advance, published in the June 14 issue of , could one day lead to the ability to direct, deliver, and store and on all-optical chips.

"We demonstrated the power of what we call resonant cavity trapping, where a particle is guided along a small waveguide and then pulled onto a micro-ring resonator," explains Kenneth Crozier, an Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS) who directed the research. "Once on the ring, optical forces prevent it from escaping, and cause it to revolve around it."

This video is not supported by your browser at this time.
Two particles are steadily trapped on a micro-ring (radius: 10 micron), and revolve around it. Credit: Courtesy of Kenneth Crozier, Harvard School of Engineering and Applied Sciences

The process looks similar to what you see in liquid motion toys, where tiny beads of colored drops run along plastic tracks—but on much smaller scale and with different physical mechanisms. The rings have radii of a mere 5 to 10 micrometers and are built using and reactive ion etching.

Specifically, is focused into a waveguide. Optical forces cause a particle to be drawn down toward the waveguide, and pushed along it. When the particle approaches a ring fabricated close to the waveguide, it is pulled from the waveguide to the ring by optical forces. The particle then circulates around the ring, propelled by optical forces at velocities of several hundred micrometers-per-second.

While using planar ring resonators to trap particles is not new, Crozier and his colleagues offered a new and more thorough analysis of the technique. In particular, they showed that using the silicon ring results in optical force enhancement (5 to 8 times versus the straight waveguide).

This is a scanning electron micrograph (SEM) of the silicon micro-ring resonator (radius: 5 micron) coupled to waveguide. Credit: Courtesy of Kenneth Crozier, Harvard School of Engineering and Applied Sciences

"Excitingly, particle-tracking measurements with a high speed camera reveal that the large transverse forces stably localize the particle so that the standard deviation in its trajectory, compared to a circle, is as small as 50 nm," says Crozier. "This represents a very tight localization over a comparatively large distance."

The ultimate aim is to develop and demonstrate fully all-optical on chip manipulation that offers a way to guide, store, and deliver both biological and artificial particles.

Explore further: Imaging electric charge propagating along microbial nanowires

Related Stories

Scientists Create Light-Bending Nanoparticles

Mar 03, 2009

(PhysOrg.com) -- Metallic nanoparticles and other structures can manipulate light in ways that are not possible with conventional optical materials. In a recent example of this, Rice University researchers ...

Using light to move and trap DNA molecules

Jan 02, 2009

(PhysOrg.com) -- A major goal of nanotechnology research is to create a "lab on a chip," in which a tiny biological sample would be carried through microscopic channels for processing. This could make possible ...

Time Lens Speeds Up Optical Data Transmission

Sep 28, 2009

(PhysOrg.com) -- Researchers at Cornell University have developed a device called a "time lens" which is a silicon device for speeding up optical data. The basic components of this device are an optical-fiber ...

Recommended for you

Researchers develop world's thinnest electric generator

Oct 15, 2014

Researchers from Columbia Engineering and the Georgia Institute of Technology report today that they have made the first experimental observation of piezoelectricity and the piezotronic effect in an atomically ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Lambduh
Jul 20, 2010
This comment has been removed by a moderator.
FullyAutoMagic
not rated yet Jul 20, 2010
First funny-ass comment aside, can anyone explain practical applications or at least future track applications of this to me? Where does it lead, in short.