The Free-space optical Inter-Rack nEtwork with high FLexibilitY — known as Firefly — architecture is a joint project of Penn State, Stony Brook University and Carnegie Mellon University.
Firefly uses infrared lasers and receivers mounted on top of data center racks to transmit information. The laser modules are rapidly reconfigurable to acquire a target on any rack.
Mohsen Kavehrad, W. L. Weiss Chair Professor of Electrical Engineering at Penn State, said human interference is minimal because the racks are more than 6.5 feet high and most workers can walk between the rows of racks without breaking the laser beams.
"It uses a very inexpensive lens, we get a very narrow infrared beam with zero interference and no limit to the number of connections with high throughput," said Kavehrad.
While fiber-optic cabling and energy expenditure for idle servers are problems, throughput is more critical. When hundreds of cables merge into a few, the data transfer bottlenecks that result reduce the speed at which the data center can deliver information. A flexible, configurable system could be the fix, reducing bottlenecks and decreasing the number of servers needed.
The engineers have created a simplified, proof-of-concept system to show that their infrared laser can carry the signal and target the receiver. They are transmitting wavelength division multiplexed — multiple signals sent by different colored lights — bi-directional data streams each carrying data at a transmission rate of 10 Gbps from a Bit Error Rate (BER) test set. BER testing determines the number of errors in a signal caused by interference, noise, distortion or synchronization problems.
Two different microelectromechanical devices containing micromirrors are used to position an infrared laser beam to target a receiver and send information. Courtesy of Patrick Mansell, Penn State.
The National Science Foundation supported the Firefly project.