SANTA CLARA, Calif. — Oracle Labs is developing a low-power laser it hopes will be a key enabler for silicon photonics. The computer company could announce the status of its work within a few months.
Oracle says silicon photonics will soon be used to link chips in high-end server cards and racks at 25 Gbit/s. It envisions a macrochip, a wafer-scale server motherboard where all major chips on the card are linked via silicon photonics. The technology is critical for plans to get power consumption on petaflop supercomputers down from 556 KW today to about 85 KW.
"Over the next five years, all [server] links will become exclusively photonic at 25G or perhaps slightly faster," A.V. Krishnamoorthy, a chief technologist for photonics at Oracle, said in a keynote at a server design event here. VCSELs are widely used today and will continue to be used, particularly in active optical cables, but "in the end, it will all be silicon photonics simply because of the need for integration and density."
Oracle worked closely with the component providers Kotura (now part of Mellanox) and Luxtera in a DARPA program on silicon photonics. Over multiple generaitons of designs, it got all the silicon photonics down to a target of 0.7 picojoule/bit, except for the laser, which consumed 1.4 pj/bit by itself (see chart below).
"We are really focused now on getting more efficient silicon-assisted lasers," Krishnamoorthy said. "There's a need in the industry for the lowest-cost laser solution. Perhaps that will determine who the winner will be" among component approaches. Oracle Labs hopes its low-cost laser will work equally well with the different silicon approaches of Kotura and Luxtera, which are "very different beasts."
Kotura started with low-loss passive platforms and worked on creating germanium-based actives and relatively large germanium wave guide detectors, which makes optical coupling of chips easier. Luxtera has an "equally appealing submicron platform with silicon based modulaiton and germanium detection." In the DARPA program, Oracle worked closely with Luxtera, developing its own PDK with the startup's foundry. Similarly, it helped Kotura develop its modulators. A followup DARPA program called POEM now involves IBM and Hewlett-Packard, as well.
Intel has been developing silicon photonics in its labs for a decade. This year, it said it will soon deliver 100G links for computer servers. Cisco Systems is also in the hunt. It has acquired a silicon photonics startup and has discussed using 2.5-D chip stacks.
"We are still early in the game to get well below a dollar per Gbit and get integration in the chip package," Krishnamoorthy said. "Those are the hard questions to answer."
The following pages show slides of Oracle's work to date.