Engineers more than double data transmission capacity over fiber-optic cables

June 29, 2015

A wideband frequency comb ensures that the crosstalk between multiple communication channels within the same optical fiber is reversible (credit: UC San Diego Photonics Systems Group)

University of California, San Diego electrical engineers have invented a technology that could allow between a two- and fourfold increase in data transmission capacity for the backbone of Internet, cable, wireless, and landline networks over long distances, while reducing cost and latency (delay).

The new system addresses a problem known as the “Kerr effect”: distortion of optical signals that travel on optical fibers over distances, requiring the laser light in fiber-optic wires to be amplified and regenerated at regular distances along the fiber to avoid transmission errors. This process is expensive and limits data transmission rates.

Eliminating crosstalk

The new findings eliminate the need for electronic regenerators. The breakthrough in this study is the researchers’ invention of custom wideband “frequency combs” that remove “crosstalk” (signal corruption) between multiple streams of information traveling long distances through the optical fiber.

“Crosstalk between communication channels within a fiber optic cable obeys fixed physical laws. It’s not random. We now have a better understanding of the physics of the crosstalk. In this study, we present a method for leveraging the crosstalk to remove the power barrier for optical fiber,” explained Stojan Radic, a professor in the Department of Electrical and Computer Engineering at UC San Diego and the senior author on the Science paper. “Our approach conditions the information before it is even sent, so the receiver is free of crosstalk caused by the Kerr effect.”

In lab experiments, the researchers at UC San Diego successfully deciphered information after it traveled a record-breaking 12,000 kilometers through fiber optic cables with standard amplifiers and no repeaters.

The photonics experiments were performed at UC San Diego’s Qualcomm Institute by researchers from the Photonics Systems Group led by Radic.

The research was published in the June 26 issue of the journal Science.

Abstract of Overcoming Kerr-induced capacity limit in optical fiber transmission

Nonlinear optical response of silica imposes a fundamental limit on the information transfer capacity in optical fibers. Communication beyond this limit requires higher signal power and suppression of nonlinear distortions to prevent irreversible information loss. The nonlinear interaction in silica is a deterministic phenomenon that can, in principle, be completely reversed. However, attempts to remove the effects of nonlinear propagation have led to only modest improvements, and the precise physical mechanism preventing nonlinear cancellation remains unknown. We demonstrate that optical carrier stability plays a critical role in canceling Kerr-induced distortions and that nonlinear wave interaction in silica can be substantially reverted if optical carriers possess a sufficient degree of mutual coherence. These measurements indicate that fiber information capacity can be notably increased over previous estimates.

E. Temprana, E. Myslivets, B.P.-P. Kuo, L. Liu, V. Ataie, N. Alic, S. Radic. Overcoming Kerr-induced capacity limit in optical fiber transmission. Science, 2015 DOI: 10.1126/science.aab1781
Electrical engineers break power and distance barriers for fiber optic communication

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