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A new type of mirror (square in center) is a fraction of the thickness of conventional mirrors used in semiconductor lasers.

Cheaper Lasers
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.

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Credit: Connie J. Chang-Hasnain

Tagged: Computing

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