Chips that can steer light

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.

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.