Faster Fiber Links for Data Centers

A new fiber-optic system can carry 800 gigabits of data per second, a big step up from top speeds of 100 or 200 gigabits in today's data centers

3 min read

Conceptual image of speedy fiber optic transmission.
Illustration: iStockphoto

Data centers that host massive amounts of content and cloud computing are at the center of the global information network. Equipment-makers are racing to keep up with the rapid growth of content and demand for bandwidth to process and distribute all of this information around the world. 

Feeding the hungry network beast has become a big business, and one of the leaders in that effort is introducing a new record-setting system this week at the Optical Fiber Communications Conference (OFC), cosponsored by IEEE, which is being held March 3 to 8 in San Diego. 

Ciena's new WaveLogic 5 Extreme system can transmit 800 gigabits of data per second on a single wavelength of light through up to 200 kilometers of optical fiber. The company says it will begin deliveries by year-end. 

Fiber-optic transmission capacity has grown at Moore's Law rates since the 1980s, helping to drive the rise of information technology. High-capacity long-haul systems have fueled network growth, most recently in the Pacific Light Cable. That system will carry a record 144,000 gigabits per second between Hong Kong and Los Angeles by sending 240 wavelengths through each of six fiber pairs when it comes online this year

However, the bulk of data carried on those big cables is now moving between corporate data centers. Facebook and Google bought shares of the Pacific Light Cable to link their data centers in Asia and North America. Data center capacities are growing faster than 10 percent a year, and stretching out among multiple buildings as the network transforms, says Helen Xenos, senior director of portfolio marketing for Ciena. Operators want to integrate cable networks connecting sites that may be tens of kilometers apart so they look seamless to users.

Much data center traffic is packaged as 100-gigabit Ethernet transmitted on one of about a hundred wavelengths in an optical fiber. But operators want to squeeze more data through the cables. The number of ports installed in data centers to carry 200 gigabits or more are expected to increase more than 50 percent a year over the next three to five years, says Jimmy Yu, a vice president at a market research firm called Dell'Oro group

At OFC, the Optical Internetworking Forum will demonstrate the interoperability of 400-gigabit transmission equipment meeting the group's new 400ZR standard. Yu expects shipments of 400-gigabit equipment, first introduced in 2017, "to grow at an exponential rate with cumulative port shipments exceeding 10 million within three years." 

'I think our engineers still have some tricks up their sleeves.'

Much of that equipment is aimed at data centers. Ciena is offering two families of systems. Its Extreme series, optimized for data rate and long-distance performance, includes the 800-gigabit model, which Xenos says can transport the full rate over 100 to 200 kilometers for data center connections, and can be adjusted to carry 600 gigabits for a thousand kilometers, or 400 gigabits for even longer hauls. It uses cutting-edge technology, including seven-nanometer CMOS digital signal processing chips and high-bandwidth electro-optics. A Nano series optimized for the small footprint and low power sought for use inside data centers can carry 100 to 400 gigabits, depending on the distance. 

Each system is a box full of optics and electronics that serves as an interface between one part of a data center and one wavelength on a fiber-optic cable. The box combines input signals from that part of the data center into a stream carrying up to 800 gigabits per second, then modulates light in one band of wavelengths transmitted on the fiber.

Another box on the other end reverses the process, converting the input optical signal to outputs intended for the part of the data center receiving the signal. Each box contains both input and output interfaces.

Improvements in digital signal processing chips allow more sophisticated modulation of the coherent light transmitted through the fiber. That can double the data rate carried on one wavelength, although at a cost of higher noise that limits transmission distance. Each fiber in a cable can carry multiple separate signals on separate wavelengths spaced a proper distance apart. 

Meanwhile, other companies have their own 800-gigabit equipment in the works. Infinera is developing a new version of its "Infinite Capacity Engine" which it says can transmit 800-gigabit signals on two separate wavelengths for a total capacity of 1.6 terabits per second for data centers and metro networks. At OFC, Infinera will show an integrated photonic circuit that will be used in the system. It also talks of using 7-nm chips. 

Another company, Neophotonics, will show key components for 800-gigabit transmitters and receiversAcacia Communications will show a module that can transmit at 1,200 gigabits, but it reaches that data rate by combining two 600-gigabit signals at different wavelengths. 

Some observers have suggested that fiber transmission capacity may be approaching its ultimate limit, but earlier warnings of ultimate limits were proved wrong when new technology came along, and Xenos predicts that will happen again. "I think our engineers still have some tricks up their sleeves," she says.  

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