A photonic switch was developed that can control the direction of light passing through optical fibers faster and more efficiently than ever. This optical “traffic cop” could improve how information travels through high-performance supercomputers used for artificial intelligence and other data-intensive applications.
The photonic switch is built with more than 50,000 microscopic “light switches,” each of which directs one of 240 tiny beams of light to either make a right turn when the switch is on, or to pass straight through when the switch is off. The 240 × 240 array of switches is etched into a silicon wafer and covers an area only slightly larger than a postage stamp.
Currently, the only photonic switches that can control hundreds of light beams at once are built with mirrors or lenses that must be physically turned to switch the direction of light. Each turn takes about one-tenth of a second to complete. The new photonic switch is built using tiny integrated silicon structures that can switch on and off in a fraction of a microsecond, approaching the speed necessary for use in high-speed data networks.
Electrical switches generate heat, so even though more transistors can be put onto a switch, the heat they generate poses certain limits. Photonic switches require very little power and don't generate any heat, so they don't face the same limitations as electrical switches; however, current photonic switches cannot accommodate as many connections and also are plagued by signal loss — essentially “dimming” the light as it passes through the switch — which makes it hard to read the encoded data once it reaches its destination.
In the new photonic switch, beams of light travel through a crisscrossing array of nanometer-thin channels until they reach these individual light switches, each of which is built like a microscopic freeway overpass. When the switch is off, the light travels straight through the channel. Applying a voltage turns the switch on, lowering a ramp that directs the light into a higher channel, which turns it 90 degrees. Another ramp lowers the light back into a perpendicular channel.
Pshotolithography was used to etch the switching structures into silicon wafers The researchers can currently make structures in the 240 × 240 array — 240 light inputs and 240 light outputs — with limited light loss.