For high speeds over long distances, optical links are already standard. Multi-gigabit carrier backbones can carry a whole city's data as waves of light, which are converted to and from electrical signals on each end. When individual servers start generating enough information, data-center architects will have to use optical technology just to connect them the top of the server rack.
We're not there yet. Even at 100Gbps, electrical interconnects can go four or five meters, enough to reach the top of a rack of servers, Linley Group's Bolaria said. And even though the need for 100-Gigabit links is starting to creep into the busiest data centers, there's still room to grow because those connections are really made up of four 25Gbps wires, he said.
But Krishnamoorthy sees a transition to optics coming. "We think that the speeds at 25-gigabit and beyond will get us to push optics onto every blade," he said.
Ultimately, Oracle wants to take photonics even beyond server interfaces. Miniaturized connections could link processors at high speed across a motherboard, Krishnamoorthy believes.
The current high cost of optical modules isn't as important for long-distance network interfaces as it is for server connections, because there are relatively few of them, according to Bolaria. But when every server needs an optical connection to a top-of-rack switch, data-center builders will need something both less expensive and smaller than a module with multiple parts to it, and that's where silicon photonics comes in, he said. Though other chip-making materials are used today in some highly integrated optical interfaces, silicon is likely to win out because of the huge industry already in place around silicon, Bolaria said.
Oracle is in good company. In addition to startups such as Luxtera, big names are pursuing silicon photonics. Cisco Systems recently acquired silicon photonics startup Lightwire, and data-center interconnect vendor Mellanox Technologies has bought another new player, Kotura. Intel is also developing data-center photonics, including through a collaboration with Facebook.
Though it's not needed yet, they're all thinking ahead, Bolaria said.
"At some point, electrical will fail to suffice for what we're trying to do," he said. "It's going to take years, so a lot of them are spending money in it now so they can be better prepared than their competitors when that happens."