If you want to create a moving light source, you have a few possibilities. One is to mount a light emitter in some kind of mechanical housing—the approach used in, say, theatrical spotlights, which stagehands swivel and tilt to track performers.
Another possibility, however, is to create an array of light emitters and vary their "phase"—the alignment of the light waves they produce. The out-of-phase light waves interfere with one another, reinforcing each other in some directions but annihilating each other in others. The result is a light source that doesn't move, but can project a beam in any direction. Such "phased arrays" have been around for more than a century, used most commonly in radar transmitters, which can be as much as 100 feet tall. But in this week's issue of Nature, researchers from MIT's Research Laboratory of Electronics (RLE) describe a 4,096-emitter array that fits on a single silicon chip. Chips that can steer beams of light could enable a wide range of applications, including cheaper, more efficient, and smaller laser rangefinders; medical-imaging devices that can be threaded through tiny blood vessels; and even holographic televisions that emit different information when seen from different viewing angles. In their Nature paper, the MIT authors—Michael Watts, an associate professor of electrical engineering, Jie Sun, a graduate student in Watts' lab and first author on the paper, Sun's fellow graduate students Erman Timurdogan and Ami Yaacobi, and Ehsan Shah Hosseini, an RLE postdoc—report on two new chips. Both chips take in laser light and re-emit it via tiny antennas etched into the chip surface.