Nanolasers. Ever-smaller lasers pave the way for data highways made of light.
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Takes the heat. Precisely grown dielectric and metallic layers are key to this semiconducting device. C R E D IT S ( T O P T O B O T T O M ): M . N E Z H A D E T A L ., N A T U R E P H O T O N IC S , P U B L IS H E D O N L IN E ( 1 8 A P R IL 2 0 1 0 ); M . T . H IL L E T A L ., O P T IC S E X P R E S S 1 7 , 1 3 ( 1 8 J U N E 2 0 0 9 ) The dream of optical computing—replacing electronic devices with much faster ones based on light—has tantalized scientists for generations. Nowadays, computer circuitry has grown too complex to be replaced wholesale. Instead, researchers talk about using lasers and other optical components as high-speed data highways between specialized electronic processors on chips. So far, lasers and other optical components have been far too big to make this integration possible. “It’s hard to integrate the two technologies when the optical devices are 1000 times larger than the electronic devices,” says Cun-Zheng Ning, a physicist at Arizona State University, Tempe. But the gap is narrowing. In recent years, researchers around the world have married traditional optical materials with metals to create lasers a mere tens of nanometers thick. Just last month, two groups reported making lasers ultrasmall in all three dimensions. “That was almost unthinkable before,” says Peidong Yang, a chemist at the University of California (UC), Berkeley. “There has been a lot of progress.” Shrinking conventional lasers long seemed all but impossible. Traditional devices produce laser light by sending photons through an optical cavity made from a “gain” material and bouncing them back and forth with tiny mirrors. Along the way, the photons cause energized electrons in the gain material to release their energy as additional photons of light with the same wavelength. Those released photons then stimulate the release of still more photons. As the avalanche grows, some of the light is allowed to leak out of one of the mirrors to produce a tight beam of photons whose waves all travel in lockstep. In most lasers, the gain region of the optical cavity is micrometers to meters in length. Photons of light can’t be confi ned to spaces smaller than half their wavelength; otherwise they leak out. Making a smaller device lase is like pouring water into a sieve. “A classical [laser] cavity does not work,” Yang says. As a result, conventional lasers and other optical components for visible light can’t be much smaller than 200 to 300 nanometers across, and most conventional optical components are much larger than that. Current transistors and other electronic devices, by contrast, include features that measure just tens of nanometers across.