Signals travel at the speed of light through optical fibers, but overall, optical communications is much slower than light speed because signals are switched on and off and routed through networks using electronic rather than light-based devices.

Scientists have been working on ways of speeding optical networks by using a second light beam to switch an information-carrying light beam, but until now these devices have either involved relatively expensive materials or been too large to fit on a computer chip.

Researchers at Cornell University have developed an all-optical silicon switch that is small enough to be made by the thousands on computer chips. The device allows one low-powered beam of light to switch another on and off.

The researchers’ all-optical switch turns on and then off in 450 picoseconds, which is about 70 times faster than emerging silicon electromechanical optical switches and has the potential to be as fast as a few picoseconds, according to the researchers.

The first practical application of the switch is likely to be in devices that route signals in fiber-optic communications networks. Today, optical signals must be converted to electrical signals that can be processed in conventional electronic chips and often converted back to optical signals for retransmission. An all-optical switch would remove the need to convert signals between optical and electrical, and so would dramatically speed the system.

The researchers’ ring resonator switch is 20 microns long and can operate with as little as 25 picojoules of energy, which makes it suitable for use in optical chips, said Lipson. A picojoule is a trillionth of a joule and is 1,000 times the energy of a single ultraviolet photon. A double A battery contains about 1,000 joules of energy.

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