"We and others tried radio frequency signalling, but the beams become wide over short distances," said Professor Mohsen Kavehrad. "Instead, we use a free space optical link. It has an inexpensive lens, we get a narrow infrared beam with zero interference and no limit to the number of connections with high throughput."
The free space optical inter-rack network, called Firefly, would use infrared lasers and receivers mounted on top of data centre racks to transmit information. The laser modules are said to be reconfigurable to acquire a target on any rack.
The team transmitted wavelength division multiplexed bi-directional data streams, each carrying data at a transmission rate of 10Gbits/s from a bit error rate test set.
The system uses microelectromechanical systems (MEMs) with tiny mirrors for rapid targeting and reconfiguring. These MEMs use small amounts of electricity from four directions to reposition the mirror that targets the receiver. The movement of the mirrors is so small it is undetectable, but the computer program quickly locates the receiver and then narrows the target to pinpoint accuracy. The laser beam can also be rapidly moved to target a different receiver.
"We are trying to come up with something reconfigurable using light instead of radio frequency," concluded Prof Kavehrad. "We need to avoid overprovisioning and supply sufficient capacity to do the interconnect with minimal switches. We would like to get rid of the fibre optics altogether."
