A new type of mirror could make lasers smaller and more efficient
Source: “A Surface-Emitting Laser Incorporating a High-Index-Contrast Subwavelength Grating”
Connie J. Chang-Hasnain et al.
Nature Photonics 1, no. 2 (February 2007): 119-122
Results: Researchers at the University of California, Berkeley, have overhauled one of the main elements of a laser: the mirror. The new mirror is thinner than its predecessors and can be made in fewer steps, simplifying the laser fabrication process and lowering costs. It is also more reflective than previous mirrors, so it could lead to more energy-efficient lasers.
Why it matters: Many consumer electronic products use optoelectronic devices such as lasers that could benefit from an efficient, thinner, cheaper mirror. The mirrors currently used in many lasers comprise more than 80 layers of alternating thin films consisting of different materials; each layer adds to the laser’s fabrication cost. The new mirror, by contrast, has only one layer.
Methods: The researchers built their mirror into a common type of laser, called a vertical-cavity surface-emitting laser, that typically consists of two mirrors sandwiching an “active region”–the area in which photons are produced when a current is applied. Photons within the active region reflect off the mirrors, and as they bounce back and forth, their intensity increases. When it gets high enough, they pass through the mirrors, producing a beam of coherent, single-color light.
The new mirror, designed by Connie Chang-Hasnain, professor of electrical engineering and computer science at Berkeley, is a grating composed of thin parallel bars of aluminum gallium arsenide, separated from the rest of the laser by air. The photons from the active region enter the aluminum gallium arsenide bars; then, because of the optical properties of the junction between the material and the air, they take a 90º turn, reflect off the other bars, come back, and make another 90º turn into the active region. There they bounce back and forth until they are sufficiently amplified, pass through the mirrors, and exit the device.
Next step: The researchers are working to integrate the mirror into a “tunable” laser, which can emit beams of varying wavelengths of light; such devices would be useful for telecommunications, and for biological and chemical sensors. In addition, they are incorporating the mirror into solar cells, in an effort to improve efficiency. Chang-Hasnain is looking for commercialization partners.
Web Browsing without a Mouse
Eye-tracking user interface could provide an alternative
Source: “EyePoint: Practical Pointing and Selection Using Gaze and Keyboard”
Manu Kumar et al.
CHI 2007, April 28-May 3, 2007, San Jose, CA
Results: Stanford University PhD student Manu Kumar has developed an easy-to-use alternative to the computer mouse: a system that allows a person to point, click, and perform everyday mouse actions by looking at a computer’s monitor and tapping a key on its keyboard.
Why it matters: User interfaces that use eye-tracking technology have been around for many years and are sometimes used by disabled people. But so far, they haven’t been easy enough to use to displace existing technologies.
Methods: The technology uses standard eye-tracking hardware: embedded in the bezel of a computer monitor are infrared light sources and a camera that captures both the movement of the user’s pupil and the reflection of the infrared light off his or her cornea. The user looks at, say, a Web link and then depresses a “hot key” on the keyboard. The area of the screen that’s being looked at becomes magnified. Then the user narrows his or her focus within the magnified region and releases the hot key, effectively clicking through to the link.
Next step: In studies in which participants were asked to type using the keyboard but move the cursor using the eye-tracking system, Kumar recorded an error rate close to 20 percent. He says many errors occur when users think they are focusing on a target that’s actually in their peripheral vision, and the eye-tracking technology instead picks up the area they’re really looking at. Kumar has developed algorithms to compensate for these errors.
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