Systems designers see high-speed optical interconnect between chips coming soon, but there's little agreement on how best to do it.
Optical interconnects from chip to board and chip to chip are starting to look like a solution to the I/O roadblock for high-speed switching within the next few years. But the industry is divided on whether to implement this disruptive optical/electronics integration on the wafer or in the package.
“High-speed signaling at lower power requires that optics get closer to the ASIC than ever before. There’s been a long history of optics displacing electrical links, from connecting networks to connecting server racks and chassis, and the next step will be connecting the chip to other chips on the board,” says John Cunningham, a hardware architect at Oracle.
He will report on Oracle’s recent work with DARPA and other partners on reduction in energy per bit with all-CMOS, silicon, photonic, chip-to-chip links in a talk at Semicon West in July.
Oracle’s approach is to put the I/O engine next to the logic chips in multichip modules, so the electronic drivers and the photonic components can each be built separately with the best-in-class technology. Optical components are then attached in the same package as the processer by hybrid integration.
Recent progress in advanced packaging with micro bumps and module substrates eases much of this modular integration. Issues still remain with laser efficiency, with precisely aligning the optical fibers with the lasers and photonics, and with developing the industrial volume processes to do so.
“The next hurdle is to show that the technology is scalable, and that the cost is competitive with electrical solutions,” Cunningham says. “This progression is on the industry roadmap to be developed over the next five years, but challenges still remain in developing all the building blocks and volume manufacturing processes.”
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