Using a recently-developed signal modulation efficiency enhancement technique, researchers at Alcatel-Lucent and Nokia Bell Labs claim to have achieved a staggering 65 terabits per second (Tbps) transmission over a 6,600 km (4,100 mile) single mode fiber in laboratory trials. With a transmission capacity reported equal to streaming more than 10 million HDTV channels at the same time, it is hoped that the technology used in these trials will help greatly increase the data-carrying capacity of transoceanic cable systems.
The technique, known as Probabilistic Constellation Shaping (PCS) technology, improves on standard data transmission methods (such as Quadrature Amplitude Modulation (QAM) used by the University of London to double fiber optic transmission distances) by sending certain signals more often and others less often to optimize signal quality.
"Constellations," in a standard data transmission sense, are patterns of digital signal combinations that are formed by multiple transmissions each sent out of phase with each other. In this way, many signals can be transmitted at the same time down an optical cable without interfering with one another.
Probabilistic Constellation Shaping technology takes this process one step further, by continuously measuring the constellations being transmitted to recognize the types of interference and distortion contained in a signal, "shaping" the pattern to reduce noise in the signal, and simultaneously increasing the throughput of data. To achieve this, the PCS system uses a combination of techniques to limit the number of high-power signal combinations (and, therefore, reduce noise) as well as employing super-sensitive dual band fiber optic amplifiers.
According to the researchers, this new method could help improve the data-carrying capacity of undersea optical fiber communications cables to help in meeting an on-going increase in the data traffic demands of consumers and business users alike. If the experimental capacity of 65 Tbps is achieved in real-world transoceanic cable systems, then the overall carrying capacity would be more than 13,000 times the capacity of the undersea amplified transatlantic system originally installed in 1995.
"The future digital existence where everyone, everything and every system and process is connected will require a massive increase in network capacity and the ability to dynamically optimize this capacity," said Marcus Weldon, president of Nokia Bell Labs & Nokia CTO. "Probabilistic Constellation Shaping extends the limits of current optical transmission by utilizing novel modulation techniques to dramatically improve the performance and capacity needed for the new digital era that will be enabled by the Future X Network."
Using similar techniques, Nokia Bell Labs, Deutsche Telekom and the Technical University on Munich recently achieved communication speeds of 1 Tb per second per channel over a standard terrestrial optical network, illustrating that even on less-than-ideal systems Probabilistic Constellation Shaping shows promise in greatly improving data transmission rates.
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