The technology could have applications in the design of microelectromechanical systems (MEMS) – nanoscale devices with moving parts – and micro-optomechanical systems, which combine moving parts with photonic circuits, said Michal Lipson, associate professor of electrical and computer engineering. Others involved in the study include postdoctoral researcher Gustavo Wiederhecker, and doctoral students Long Chen and Alexander Gondarenko.

silicon_nitride.jpg

“The challenge is that large optical forces are required to change the geometry of photonic structures,” Lipson explained.

But the researchers reduced the force required by creating two ring resonators – circular waveguides whose circumference is matched to a multiple of the wavelength of the light used – and by exploiting the coupling between beams of light traveling through the two rings.

A beam of light consists of oscillating electric and magnetic fields, and these fields can pull in nearby objects, a microscopic equivalent of the way static electricity on clothes attracts lint. This phenomenon is exploited in “optical tweezers” used by physicists to trap tiny objects.

The forces tend to pull anything at the edge of the beam toward the center.

When light travels through a waveguide whose cross section is smaller than its wavelength, some of the light spills over, and with it the attractive force. So parallel waveguides close together, each carrying a light beam, are drawn even closer, much like two streams of rainwater on a windowpane that touch and are pulled together by surface tension.

The researchers created a structure consisting of two thin, flat silicon nitride rings about 30 µm (millionths of a meter) in diameter mounted one above the other and connected to a pedestal by thin spokes. Think of two bicycle wheels on a vertical shaft, but each with only four thin, flexible spokes. The ring waveguides are three microns wide and 190 nm thick, and the rings are spaced 1 µm apart.
When light at a resonant frequency of the rings, in this case infrared light at 1533.5 nm, is fed into the rings, the force between the rings is enough to deform the rings by up to 12 nm, which the researchers showed was enough to change other resonances and switch other light beams traveling through the rings on and off. When light in both rings is in phase – the peaks and valleys of the waves match – the two rings are pulled together.

When it is out of phase, they are repelled. The latter phenomenon might be useful in MEMS, where an ongoing problem is that silicon parts tend to stick together, Lipson said.

An application in photonic circuits might be to create a tunable filter to pass one particular optical wavelength, Wiederhecker suggested.

The work is supported by the National Science Foundation (NSF) and the Cornell Center for Nanoscale Systems. Devices were fabricated at the Cornell Nanoscale Science and Technology Facility, also supported by NSF.

The research appears in the online edition of the journal Nature.

For more information, visit: www.cornell.edu

via Light Moves Nanostructures (photonics.com | Nov 2009 | News and Features).

The Oxford University research team, funded by the UK Medical Research Council, genetically engineered the fruit flies so that a small set of nerve cells in the brains would “fire” in response to a flash of laser light. This showed which cells are involved in how a fruit fly learns and remembers what to avoid, and offers an exciting new opportunity to investigate how memories are formed.

The Oxford scientists, with colleagues at the University of Virginia, Charlottesville, demonstrated that they could use flashes of laser light to train flies to dislike a certain odor.

“We tracked the flies using a video camera as they moved around a small chamber while two different odors were fed into the chamber from either end. We found that we could implant a lasting preference for one odor over the other by remotely activating a specific set of brain cells each time a fly strayed into a particular odor,” said Dr. Adam Claridge-Chang, who is now at the Wellcome Trust Centre for Human Genetics at Oxford University.

Using this method, the researchers were able to pinpoint the precise nerve cells that are responsible for telling the flies that they’ve done wrong, narrowing down the search from the 100,000 cells in the brain of a fruit fly to a set of just 12 neurons.

“Surprisingly, the source of these signals is in a limited number of cells – just twelve,” said professor Miesenböck. “These cells send the signals that train the fly to associate the odor with something bad, so wherever their signals go must be the seat of memory. We can now follow this up and start to characterize the process by which memories are formed and organized.”

The results of the study are published in the journal Cell. While this work has been done in fruit flies, general lessons about how actions are learned and memories are stored should hold true for humans.

“Biology teaches us that fundamental mechanisms tend to be conserved. Learning about the storage of memories from brain cells in flies should tell us a lot about how they are stored in humans,” said Miesenböck.

He has pioneered this method of genetic engineering to remote control the action of specific cells within tissues, or whole organisms like worms, fruit flies, fish and mice, using light from the outside. These efforts have given rise to a new field sometimes called “optogenetics,” to indicate that sensitivity to light is encoded genetically.

A separate paper by Miesenböck summarizing the status of this new field has also been published in Science. As the ability to write memories directly to the brains of fruit flies demonstrates, optogenetic techniques have particular power in neuroscience.

“The great advantage is that we are no longer just passive observers of processes in the brain. In the past, neuroscientists had to be content with recording the chatter of brain cells and trying to infer what it all meant. The ability to talk back and influence behavior directly is proving quite valuable,” Miesenböck said.

via Lasers Twist Fly Memories (photonics.com | Oct 2009 | News and Features).

Optical discs have been a leading storage solution for decades

A disc that can store 500 gigabytes (GB) of data, equivalent to 100 DVDs, has been unveiled by General Electric.

The micro-holographic disc, which is the same size as existing DVD discs, is aimed at the archive industry.

But the company believes it can eventually be used in the consumer market place and home players.

Blu-ray discs, which are used to store high definition movies and games, can currently hold between 25GB and 50GB.

Micro-holographic discs can store more data than DVDs or Blu-ray because they store information on the disc in three dimensions, rather than just pits on the surface of the disc

A single GE disc could be used to package up a library of high definition movies but is there pent-up consumer demand for such an offering? News website Technology editor Darren Waters Read more on the Dot.Life blog

The challenge for this area of technology has been to increase the reflectivity of the holograms that are stored on the discs so that players can be used to both read and write to the discs.

Brian Lawrence, who leads GE’s Holographic Storage said on the GE Research blog: “Very recently, the team at GE has made dramatic improvements in the materials enabling significant increases in the amount of light that can be reflected by the holograms.”

More capacity

The higher reflectivity that can be achieved, the more capacity for the disc. While the technology is still in the laboratory stage, GE believes it will take off because players can be built which are backwards compatible with existing DVD and Blu-ray technologies.

In a statement the firm said: “The hardware and formats are so similar to current optical storage technology that the micro-holographic players will enable consumers to play back their CDs, DVDs and Blu-ray discs.”

”GE’s breakthrough is a huge step toward bringing our next generation holographic storage technology to the everyday consumer,” said Mr Lawrence in a statement.

He added: “The day when you can store your entire high definition movie collection on one disc and support high resolution formats like 3D television is closer than you think.”

Micro-holographic technology has been one of the leading areas of research for storage experts for decades. Discs are seen as a reliable and effective form of storage and are both consumer and retail friendly.

However, General Electric will need to work with hardware manufacturers if it is to bring the technology to the consumer market.

The relatively modest adoption of Blu-ray discs sales globally might be an issue with some companies who believe digital distribution and cloud computing is the long-term answer to content delivery and storage.

“This is truly a breakthrough in the development of the materials that are so critical to ultimately bringing holographic storage to the everyday consumer,” said Mr Lawrence.

via Optical disc offers 500GB storage

今年的诺贝尔物理学奖集中在光电子技术领域。其中，高锟的获奖理由为“在光学通信领域光在光纤中传输方面所取得的开创性成就”。另外两位美国科学家共同获得另一半奖金，获奖理由为“发明了一种成像半导体电路，即CCD（电荷耦合器件）传感器（用于数码成像的感光和传输器件）”。

早在1966年，高锟就在一篇论文中首次提出用玻璃纤维作为光波导用于通讯的理论。简单地说，就是提出以玻璃制造比头发丝更细的光纤，取代铜导线作为长距离的通讯线路。这个理论引起了世界通信技术的一次革命，为现代光纤通信技术的发展和应用做出了重要贡献。随着第一个光纤系统于1981年成功问世，高锟“光纤之父”的美誉传遍世界。