By sending data at a rate of 64 Gb/s over a cable 57 meters long using a vertical-cavity surface-emitting laser (VCSEL), the researchers achieved a rate that was around 14 percent faster than the previous record and about 2.5 times faster than the capabilities of typical commercial technology.
To send the data, the researchers used standard non-return-to-zero (NRZ) modulation. "Others have thought that this modulation wouldn't allow for transfer rates much faster than 32 Gb/s," said researcher Dan Kuchta of the IBM T.J. Watson Research Center in New York. Many researchers thought that achieving higher transmission rates would require turning to more complex types of modulation, such as pulse-amplitude modulation-4 (PAM-4).
"What we're showing is that that's not the case at all," Kuchta said. Because he and his colleagues achieved fast speeds even with NRZ modulation, he added, "this technology has at least one or two more generations of product life in it."
Following this achievement it is expected that standard, existing technology for sending data over short distances should be able to meet the growing needs of servers, data centers and supercomputers through the end of this decade.
To achieve such high speeds, the researchers used the VCSEL lasers developed at Chalmers University of Technology in Sweden and custom silicon-germanium chips developed at IBM Research. "The receiver chip is a unique design that simultaneously achieves speeds and sensitivities well beyond today's commercial offerings," Kuchta explained. "The driver chip incorporates transmit equalization, which widens the bandwidth of the optical link. While this method has been widely used in electrical communication, it hasn't yet caught on in optical communication," he said.