Researchers at the University of California, Santa Barbara (UCSB), have designed a silicon-based laser that emits ultrashort pulses of light at high frequencies--two characteristics that are crucial if silicon-based lasers are to become practical. Eventually, the researchers hope that the new laser could replace other, more expensive lasers in optical communication networks. It could even lead to faster computers that shuttle data around using light instead of electricity.

Modern telecommunications networks use three distinct gadgets--lasers, modulators, and detectors--to produce, encode, and detect light. Currently, all three are made of nonsilicon semiconductors, such as indium phosphide, that are difficult to mass-produce; as a consequence, they tend to be expensive and bulky. But if they could instead be made from silicon, they could be integrated on individual chips, says John Bowers, professor of electrical and computer engineering at UCSB. Devices that currently cost hundreds of dollars each could then be made in bulk for pennies, and the cost of bandwidth would plummet. The one snag in the plan is that it's hard to make silicon produce light.

In September 2006, however, the UCSB team and Intel announced a new hybrid laser that, although it still used indium phosphide, was built on a silicon base. (See "Bringing Light to Silicon.") The manufacture of the device began with a wafer that consisted of a layer of silicon dioxide sandwiched between two layers of silicon. In the top layer of silicon, the researchers etched a channel, called a waveguide, within which light bounced back and forth. To the top of the wafer, they bonded strips of indium phosphide, using a layer of glass glue only 25 atoms thick. Adding this additional layer, says Bowers, isn't much different from adding layers of other materials to silicon, something that's regularly done in today's manufacturing process.

To turn the laser on, the researchers applied electrical current to metal contacts on top of the indium phosphide. Indium phosphide is a naturally light-emitting material, so the strips of it on top of the wafer produced photons that got trapped in the channel below, bouncing back and forth along the length of the silicon waveguide. In certain materials, that bouncing is enough to amplify normal light into laser light, but not in silicon. So the device was designed to let a small amount of light, called the evanescent tail, sneak back into the indium phosphide, where it was amplified. The benefit of this design is that it avoids the costly fabrication of an indium-phosphide waveguide.

For the new laser, which is described in a recent issue of Optics Express, the researchers made their design slightly more complex. "We needed to turn it into a device with multiple sections," explains Alexander Fang, a graduate student who worked on the project. He says that he had to make sure the lengths of the cavities were precise, and that regions that amplified light and absorbed light were electrically isolated from each other.

Neuro engineering

Silicon Brains
Computer chips designed to mimic how the human brain works could shed light on our cognitive capacities.

Kwabena Boahen's lab at Stanford University is spotless. A lone circuit board, housing a very special chip, sits on a bare lab bench. The transistors in a typical computer chip are arranged for maximal processing speed; but this microprocessor features clusters of tiny transistors designed to mimic the electrical properties of neurons. Read More
Raising Consciousness
Some seemingly unconscious patients have startlingly complex brain activity. What does that mean about their potential for recovery? And what can it tell us about the nature of consciousness?
Next-Generation Retinal Implant
Scientists plan to test an implanted chip with four times the resolution of the previous version in people blinded by retinal degeneration.
Finding Hidden Tumors
Doctors at Massachusetts General Hospital are using whole-body MRI to illuminate a tricky disease.
MRI: A Window on the Brain
Advances in brain imaging could lead to improved diagnosis of psychiatric ailments, better drugs, and earlier help for learning disorders.
A Brain Chip to Control Paralyzed Limbs
Research is under way to make a brain chip capable of triggering muscle movement.
Brain Chips Give Paralyzed Patients New Powers
A neural implant allows paralyzed patients to control computers and robotic arms -- and, maybe one day, their own limbs.
Brain Electrodes Help Treat Depression
Studies suggest that deep brain stimulation could effectively treat depression.

Researchers at Microsoft and Mitsubishi are developing a new touch-screen system that lets people type text, click hyperlinks, and navigate maps from both the front and back of a portable device. A semitransparent image of the fingers touching the back of the device is superimposed on the front so that users can see what they're touching.

Multitouch screens, popularized by gadgets such as PDAs and Apple's iPhone, are proving to be more versatile input devices than keypads. But the more people touch their screens, says Patrick Baudisch, a Microsoft researcher involved in the touch-screen project, the more content they cover up. "Touch has certain promise but certain problems," he says. "The smaller the touch screen gets, the bigger your fingers are in proportion ... Multitouch multiplies the promise and multiplies the problems. You can have a whole hand over your PDA screen, and that's a no go."

The current prototype, which illustrates a concept that the researchers call LucidTouch, is "hacked together" from existing products, says Daniel Wigdor, a researcher at Mitsubishi Electric Research Lab and a PhD candidate at the University of Toronto. The team started with a seven-inch, commercial, single-input touch screen. To the back of the screen, they glued a touch pad capable of detecting multiple inputs. "This allowed us to have a screen on the front and a gesture pad [on the back] that could have multiple points," says Wigdor. "But what that didn't give us was the ability to see the hands." So, he says, the researchers added a boom with a Web camera to the back of the gadget.

The image from the Web camera and the touch information from the gesture pad are processed by software running on a desktop computer, to which the prototype is connected. The software subtracts the background from the image of the hands, Wigdor explains, and flips it around so that the superimposed image is in the same position as the user's hands. Additionally, pointers are added to the fingers so that a user can precisely select targets on the touch pad that might be smaller than her finger. In October, a paper describing the research will be presented at the User Interface Software and Technology symposium in Rhode Island.

Admittedly, this prototype has several limitations. Most glaringly, it's impractical to attach a boom and camera to the back of a handheld device. In their paper, the researchers suggest a number of different approaches for more-compact LucidTouch prototypes. The gesture pad on the back could actually provide an image of the user's fingers as well as touch information, explains Wigdor. The pad uses an array of capacitors, devices that store electrical charge. Fingers create a tiny electrical field that changes the capacitance of the array, depending on their distance from it. This distance can be tuned, says Wigdor, so that the pad can register the entire finger, and not just the fingertip touching it. Another approach, he says, would be to use an array of tiny, single-pixel light sensors that could map fingers' locations. Or the device could use an array of flashing, infrared-light-emitting diodes; sensors would then detect the light's reflection off of a hand, Wigdor explains.

As touch screens shrink, says Scott Klemmer, a professor of computer science at Stanford University, one of the biggest problems users face is inadvertently covering up content with their fingers. LucidTouch, he says, "distinguishes itself in two ways: first, it provides better feedback about where you are ... and the other distinction is that it's multitouch."

Even with their prototype's cumbersome design, the researchers were able to write applications for it and gather user responses from a small group. Depending on the application, users found that touching the back of the screen could be useful. For instance, most preferred to type on a Qwerty keypad using the front of the screen. But when the keypad was split down the middle, and one half was placed vertically along each side of the screen, most preferred to type on the back of the device. Half of the participants preferred using the back of the device for tasks such as dragging objects and navigating maps. The users were also divided on whether the superimposed images of their fingers were helpful. Two-thirds of the participants preferred the superimposed images when using the keyboard and dragging objects, and half preferred them while using the map.

These results suggest that a user's preference for LucidTouch and pseudo-transparency depends on the application. Baudisch suspects that one of the first places that this technology could appear is in portable gaming, where specific games could be written for the technology. But importantly, it could enable people to start thinking differently about the potential of multitouch screens on handhelds.

"I think--zooming out for a moment--what's really exciting about this time is that for so many years, we've seen the dominance of the mouse," says Stanford's Klemmer. "I think that hegemonic situation is now over. What this points to for me is the idea that we're going to see this increased diversity of devices that adapt to different situations."

Uncrating a 103-inch Panasonic Plasma (Gallery)

You don't unbox a 103-inch plasma, you uncrate it. Today, during our sortie to Secaucus, I got a chance to wander deep into the caverns of Panasonic HQ to the highly secure Big Service locker, see where they stash the 103-inch TVs. I got to check out one from the back—a rare treat, since when they are on tour, they are mounted with only the fronts visible. This may be the very first public look at the