In a recent presentation at a San Francisco conference on optics and photonics, researchers presented papers describing their successful tests of optical data transmission tools, which soon may replace current data centers’ thousands of miles of fiber-optic cables with overhead layer of infrared laser beams, lenses and mirrors.
In one Jan. 31 presentation at Photonics West 2017 and in a follow-up interview, Mohsen Kavehrad, a Penn State University electrical engineering professor who is working on the National Science Foundation-supported project, said a data center’s controlled environment overcomes many of the atmospheric challenges that hinder free-space optical data transmission systems.
Kavehrad and his Stony Brook and Carnegie Mellon researcher partners are testing the use of micromechanical systems (MEMs). Using wide-angle infrared receiving lenses, these tiny, computer-adjustable mirrors make it possible to quickly aim and accurately shoot laser beams across mile-long server rooms to link specific server racks with targeted data streams.
Kavehrad says the technology could make obsolete the bundles of fiber-optic cable and switches that are now laced throughout data centers, which are just beginning to reach capacity as they struggle with the demands of today’s data-intensive systems. “Fiber is running out of juice,” he says. “The only solution is to add bundles, and, already, it’s like a jungle in there.
“We are working with Google and Linked-In,” adds Kavehrad. “They are our industry partners in the award we received from the National Science Foundation.”
Kavehrad says other researchers are working on related technology. For example, Microsoft Research Lab is developing a system that bounces data-laden laser beams off mirrors on the ceiling, sending the data from the top of one server stack to another. “They call [their system] Disco Balls—micromirrors on the ceiling,” he says.
Kavehrad and his partners are testing components for the system that they call a “free-space optical inter-rack network with high flexibility,” nicknamed “Firefly.”
Kavehrad says it uses very narrow infrared laser beams and MEMs to target “a very inexpensive wide-angle lens.” The combination of the 10º adjustability of the MEMs and the wide-angle receiving lenses makes it possible to swing the signal-carrying beams across a 40º arc, shifting the target from one rack top to another. “I can send a pencil beam to another top of the rack, and then I can shift the angle of departure from that laser source and hit another part of the rack,” he says. “It’s very fast, and you can aim, shoot and hit the target. And it’s all adaptive—slight movement, such as vibration, is not going to cause any problem.”
And unlike transmitting data over radio waves, laser beams experience “zero interference and no limit to the number of connections, with high throughput,” he says. “Photons are neutral particles. Unlike electrons, they do not interfere with each other. They can even cross beams. The only time you can create interference is if you shine a flashlight at a receiver.”
Further, when moving data inside a server farm, direct optical connection will increase capacity by eliminating the need for the addressing data of packet-switching transfer and error-checking schemes used over the internet, Kavehrad says.