A new way of controlling the path that light takes as it passes through silicon could help overcome one of the big obstacles to making an optical, rather than electronic, computer circuit. Researchers at Caltech and the University of California, San Diego, have taken a step toward a device that prevents light signals from reflecting back and causing errors in optical circuits.
Chips that compute with light instead of electrons promise to be not only faster, but also less expensive and more energy-efficient than their conventional counterparts. But to be made economically, many believe, photonic chips must be made from silicon, using equipment already being used to build electronic microchips.
Researchers have made many of the necessary elements for a silicon photonic circuit already, including superfast modulators for encoding information onto beams of light, and detectors to read these beams.
But the way light travels through silicon remains a big problem. Light doesn't just go in one direction—it bounces around and even reflects backward, which is disastrous in a circuit. If an optical device were designed to receive two inputs and a third input reflected back in, that would cause an error. As a circuit became more complex, error-causing reflections would overwhelm it.
The Caltech and UCSD researchers have developed a silicon waveguide that causes light to behave differently depending on the direction it's traveling. The researchers, led by Caltech electrical engineering professor Axel Scherer, created a waveguide out of a long, narrow strip of silicon about 800 nanometers wide, with metal spots along the sides like bumpers. Light travels freely in one direction down the waveguide, but is bent as it travels in the opposite direction.