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Optical signals control mechanical structures

Posted: 07 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:optical signal? MEMS? nanoscale structure?

While micro- and nanoscale mechanical structures have long been used to sculpt and channel optical signals, from waveguides to resonators, the roles have lately been reversed.

Researchers at both the Massachusetts Institute of Technology (MIT) and Cornell University have recently demonstrated new methods of using optical signals to control mechanical structures and at least one group of material scientists proposing to close the feedback loop.

The trend began many years ago with the invention of "optical tweezers" to manipulate living cells without damaging them. Now MIT engineers Matthew Lang, a professor, and David Appleyard, a doctoral candidate, have demonstrated next-generation technology: an optical tractor-beam that can manipulate both living cells and microelectromechanical systems (MEMS) structures as large as 20?m. "We've begun applying optics to building structures on chips," said Lang.

Separately, Cornell University professors Michal Lipson and David Erickson, along with their graduate students Bradley Schmidt and Allen Yang, report harnessing the evanescent field surrounding solid-core optical fibers to attract and propel micro- and nanoscale particles through microfluidic devices. Lipson, a pioneering researcher who manages a team of EEs conducting silicon photonics research, collaborated with mechanical engineer Erickson to characterize the velocities that can be achieved for various particle sizes, reporting that speeds of 28?m/s were achieved for 3?m-diameter polystyrene spheres using about 54mW of optical power down the fiber.

Back at MIT, in a separate lab, EE professor Erich Ippen teamed with physics professor Marin Soljacic and their graduate students Milos Popovic and Peter Rakich, to unify the influence of optics-on-mechanical with mechanical-on-optics by closing the feedback loop between the two. The researchers have crafted a control theory detailing how feedback from mechanically coupled optical cavities can be used to dynamically tune their resonance.

"We hope to eventually demonstrate working MEMS devices that can perform all-optical functions not possible today, from switching to adaptive dispersion and filter synthesis for applications like optical clock recovery," said Popovic.

The team is now crafting MEMS membranes and cantilevers that can perform signal processing operations presently requiring expensive translation to electrical signals and back to optical, such as resonators that can track communications signals across their entire free spectral range of about 4.5THz.

- R. Colin Johnson
EE Times

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