Researchers from Australia, Denmark, and China have combined efforts to show the feasibility of terabit-per-second Ethernet over fiber-optic cables. The solution involves a photonic chip that uses laser light for switching signals, and a form of the exotic material type, chalcogenide.
The groups' combined efforts are documented in a paper in the February 16, 2009, issue of Optics Express, which details a demonstration of 640 Gbps networking and the extension of the same approach to terabit-per-second speeds. (See "Breakthrough switching speed with an all-optical chalcogenide glass chip: 640 Gbit/s Demultiplexing," Leif Oxenl�we et al, Optics Express, Vol. 17, Issue 4.)
Ben Eggleton, the research director for Australia's Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS), said that the problem isn't injecting that much high speed data into an optical strand, called multiplexing, but retrieving data at such high rates.
Individual lasers, operated by conventional electronics, can inject dozens of 10 Gbps streams, but in terms of retrieving that multiplexed data "at these very very high bit rates, beyond 40 Gbps, electronics is not fast enough," Eggleton said.
In conjunction with a Danish research organization at the Technical University of Denmark, which has been working on high-speed optical networking, CUDOS developed a photonic integrated circuit that uses lasers and light in the same way a conventional electronic integrated circuit uses electrons and transistors.
Eggleton said that this multiplexing uses optical time division multiplexing (OTDM) which allows separation over time of signals over the same medium. The modulation of separate, closely spaced wavelengths of light allows a fairly massive increase in capacity over today's systems, which can carry Gbps on each of several widely spaced wavelengths.
One of the key breakthroughs researchers made wasn't so much in speed but in practicality. By using relatively traditional methods to etch a circuit out of a glassy form of a chalcogenide, arsenic trisulfide (As2S3), researchers were able to reduce the waveguide that demultiplexed an incoming signal from tens of meters down to 5 cm.
Eggleton noted that non-linearity in a material is a key necessity in reducing a waveguide's length, and that CUDOS's materials research led it to the compound the group employed. "We've found a material that has 1,000 times more of this non-linearity" than previous approaches, Eggelton said. "That allows us to achieve the same processing on a single chip" instead of spools of fiber-optic cable, as a previous high-water mark of fiber transmission rates had entailed.
Construction of a monolithic chip that could handle 640 Gbps and faster speeds would require a separate waveguide for each 10 Gbps stream.
Eggleton said that silicon-based chips could also be used in principle to achieve similar, but slower, results, but their ultimate goal was to create fully photonic chips in the same foundries that now make CMOS (complementary metal oxide semiconductor) integrated circuits.
"It's years to complete," Eggleton said, taking these research efforts into a production technology. But these demonstrations "are starting to establish this is a serious proposition."