​With an infrared rainbow, IBM optical chip outpaces copper wires

IBM Research engineers have pushed a step ahead with a technology called silicon photonics designed to loosen up bottlenecks in the computing industry.

Silicon photonics marries conventional chip technology with the superfast data-transfer abilities of fiber optics. Sending data as light over optical links instead of electrons over copper wires offers big advantages in both speed and transmission distance, but because it's expensive, it's mostly limited to long-haul uses like connecting computers in different buildings, cities and continents.

But IBM's researchers demonstrated a computer chip that can simultaneously transmit and receive four different colors of infrared light over a single fiber-optic line -- a technology called multiplexing. Each link can transmit 25 gigabits of data per second, for a total of 100Gbps. That's enough to transfer a Blu-ray disc's full-resolution 25 gigabyte movie every 2 seconds.

This multiplexing-based speed, combined with the chip's all-in-one design, is an industry first, IBM said in an announcement Tuesday.

It's only a demonstration chip from a research lab at this stage, but silicon photonics work from companies like IBM, Intel and Luxtera could play a crucial role in advancing services like Google search, Microsoft Office Online and Facebook social networking that are housed in mammoth data centers packed with thousands of servers. Those servers today are often linked with copper lines, but more economical fiber-optic links could help unify those servers into a larger, more powerful block of computing power. That means more sophisticated online services.

"People would love to have a way to do inexpensive silicon-compatible photonics," said Linley Group analyst David Kanter. But the technology hasn't been easy to develop, he said.

Silicon photonics dovetails with a number of technologies like spintronics, exotic carbon materials and quantum computing that are in development to ensure the computing industry can keep up its steady pace of progress even after conventional silicon runs out of steam. The steady progress is embodied in a 50-year-old observation called Moore's Law named after Intel co-founder Gordon Moore.

Commercial use later

IBM Research typically works a step ahead of what's commercially feasible, but Big Blue expects the work will pay off for the company later.

"Making silicon photonics technology ready for widespread commercial use will help the semiconductor industry keep pace with ever-growing demands in computing power driven by big data and cloud services," said Arvind Krishna, senior vice president and director of IBM Research. So-called big-data services rely on computationally intense analysis that reveals patterns in things like shopping, traffic or product demand.

The four-link technique could cut data-center fiber-optic costs roughly in half, said Will Green, manager of IBM Research's Silicon Photonics Group.

"Multiplexing four wavelengths into one optical fiber means that you can carry four times as much data per fiber, and therefore will need four times less fiber in your interconnect system," Green said. "This fact translates into an additional system-level cost savings for the data-center application on the order of two times on the cost of installed fiber."

Longer-term future

In the longer run, fiber-optic links could tie together components within a computer, too.

Power-consumption limits have capped the speed of processors -- few chips ever make it past 4GHz these days, meaning that their internal clock speed ticks 4 billion times per second. As a result, computing engineers have been looking for other ways to improve overall system performance, and silicon photonics could play a role in keeping processors fed with the data they need to work at maximum efficiency instead of spending large fractions of their time idle.

Key to silicon photonics will be bringing the optical transmitters and receivers -- transceivers -- closer to the processors that need to send and receive data. Those components eventually will be stacked one atop another, linked with a technology called a through-silicon via (TSV), said An Steegen, senior vice president of process technology at Imec, a large Belgian-based chip research group. It'll take years to bring that idea to fruition, she predicted.

Intel has had a long-running interest in silicon photonics and with a technology called Light Peak hoped to build an inexpensive fiber-optic link for computers. It never commercialized that project, though, instead partnering with Apple on the Thunderbolt technology that uses either copper or fiber-optic links that today reach up to 40Gbps.

That's pretty fast, but copper has significant length limits. Copper Thunderbolt cables can reach 3 meters, but fiber-optical alternatives from Corning are available in lengths up to 60 meters.