Record-breaking signal transmission capacity paves the way for faster Internet

February 18, 2016, Optical Society of America

The amount of data traffic on the internet and between servers in datacenters has exploded in the past few decades and shows no signs of slowing down. For example, Ethernet technology, used in small to medium-sized networks, has evolved from an original speed of 2.94 megabits per second to 100 gigabits per second, an increase of more than 3,000-fold. An IEEE 400 Gb/s Ethernet Task Force has been formed to take the standard up to 400 gigabits per second in the next year or so, and even this may not be enough for some especially data-heavy companies.

Now, researchers from ZTE USA, Inc., New Jersey, USA, have set a new capacity record for a certain type of link that could be used to connect segments of the internet, as well as connect servers in a datacenter. The team sent 560 gigabits per second over two kilometers of single mode optical fiber, a type of fiber used for long-distance links. The researchers' solution is a low-cost and low-power optical solution that hinges on a unique combination of modulation techniques, which are used to encode digital data in an analog carrier, like light. The researchers will present their innovation at the Optical Fiber Communication Conference and Exhibition (OFC), held 20-24 March in Anaheim, California, USA.

Sending data over optical cables, as opposed to traditional coax cables or copper wires, can achieve much higher data densities and longer distances. Moreover, optical links are unaffected by electromagnetic interference and consume less power, which is becoming increasingly important as data rates continue to rise. However, the standards for encoding data in optical signals will need to evolve in order to meet increased demand for bandwidth hungry applications.

"For the existing optical network [used in industry], the modulation format is still On-off keying (OOK), which is impossible to realize 100 gigabits per second or beyond in optical inter-connection due to devices' bandwidth limitation," said Fan Li, primary author and scientist, ZTE USA, Inc. On-off keying refers to the simplest form of amplitude modulation that represents digital data as the presence (binary one) or absence (binary zero) of the signal.

Li explained that their scheme adopts a higher level, broadband multicarrier modulation method called Orthogonal Frequency-Division Multiplexing (OFDM), which transmits multiple data streams over a common broadband medium such as fiber optic cable and offers superior performance such as higher data capacity and faster data transmission speed in a given bandwidth over older, more traditional single-carrier modulation methods.

"400 gigabits per second is the next generation transmission speed for optical inter-connection. It's the first time we realize 560 gigabits per second signal transmission with OFDM technology," Li said.

Jianjun Yu, Director, ZTE USA, Inc. explained that the OFDM modulation method is suited to today's high-speed data requirements and operation in the ultra-high frequency and microwave band, and thus have been adopted for almost all the new wireless technologies nowadays. However, OFDM does have a drawback: a large peak-to-average power ratio (PAPR), meaning the instantaneous peak power of an OFDM signal is much bigger than the average power due to the coherent addition of multiple data streams or subcarriers. This characteristic leads to poor network performance at high frequencies due to the inter-connect power attenuation.

In order to improve the inter-connect performance, the researchers employed a special case of OFDM called Discrete Fourier Transform-spread (DFT-spread) orthogonal frequency-division multiplexing (OFDM), and a technique implemented in the calibration stage called Pre-equalization, which jointly overcome power attenuation in high frequency domain and reduce the peak-to-average power ratio of OFDM.

Another key part of the experimental configuration is a four-channel coarse wavelength division multiplexing (CWDM) scheme, which effectively realizes low-cost, low-power and high capacity transmission for optical signals in the inter-connection. "Coarse" means the channel spacing is more than two nanometers.

Combined with 128-QAM Orthogonal Frequency-Division Multiplexing (OFDM) – a high order OFDM modulation format for electric signals – the four-channel coarse wavelength division multiplexing (CWDM) architecture achieves the highest data transmission capacity within the same bandwidth. Each channel transmits 140 gigabits per second 128-QAM OFDM signals, for a total of 560 per second from four channels.

"Our study is the first to use Discrete Fourier Transform-spread (DFT-spread) orthogonal frequency-division multiplexing (OFDM) technology to realize optical inter-connection and achieve the largest capacity signal transmission ever reported," Li said. "The experimental results indicate that it is feasible to utilize the transceivers to realize cost-effective two-kilometer single fiber mode (SFM-28) link to satisfy the 400-gigabit Ethernet standard."

Li noted the potential application of the novel configuration lies in communication between transport networks and core routers, important components of the internet, as well as faster communication within datacenters. "For example, companies like Google or Amazon use different high-performance servers to sort high volumes of customer profiles and other useful information. The data exchanges between these servers are large and frequent, [so] high speed and high transmission capacity optical inter-connection is a good candidate for the datacenter."

The researchers' next step, Li said, is to reduce the computational complexity in the configuration and realize a real application-specific integrated circuit (ASIC) system.

Explore further: Terahertz wireless technology could bring fiber-optic speeds out of a fiber

More information: Presentation: "Demonstration of Four-Channel CWDM 560 Gbit/s 128QAM-OFDM for Optical Inter-connection," by Fan Li, Zizheng Cao, Xinying Li, and Jianjun Yu.

Related Stories

Record for fastest data rate set

February 11, 2016

A new record for the fastest ever data rate for digital information has been set by UCL researchers in the Optical Networks Group. They achieved a rate of 1.125 Tb/s as part of research on the capacity limits of optical transmission ...

Fiber Optical Transmission In Demand Of Higher Capacity

April 2, 2010

( -- With the increasing high volume content over the internet, such as multimedia and high definition images, new transmission methods need to be found to handle the increasing data demand. Nippon Telegraph and ...

Recommended for you

Cryptocurrency rivals snap at Bitcoin's heels

January 14, 2018

Bitcoin may be the most famous cryptocurrency but, despite a dizzying rise, it's not the most lucrative one and far from alone in a universe that counts 1,400 rivals, and counting.

Top takeaways from Consumers Electronics Show

January 13, 2018

The 2018 Consumer Electronics Show, which concluded Friday in Las Vegas, drew some 4,000 exhibitors from dozens of countries and more than 170,000 attendees, showcased some of the latest from the technology world.

Finnish firm detects new Intel security flaw

January 12, 2018

A new security flaw has been found in Intel hardware which could enable hackers to access corporate laptops remotely, Finnish cybersecurity specialist F-Secure said on Friday.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.