The new technology of noise reduction allows you to transfer 400 Gb / s over fiber for 12,800 km without signal repeaters

Scientists from Bell labs have developed and tested a new way to combat noise and distortion when transmitting an optical signal. They demonstrated an effective data transfer rate of 400 Gb / s over a distance of 12,800 kilometers. The principle of operation of the noise cancellation system resembles a balanced (symmetrical) connection used in audio equipment for a long time - the signal is divided into two parts, one of them is transmitted as usual, and the second is in antiphase. On the receiving side, the second part turns over again and folds with the first. As a result, the distortion and interference that fell into both signals are mutually destroyed, and the signal itself is amplified by 6 dB:



In fiber optics, everything happens in approximately the same way, only the main wave and its “twin” are transmitted in antiphase in mutually perpendicular polarization planes. Due to this, the level of nonlinear distortion was reduced by 8.5 dB. In the course of the main experiment, using wave compaction of channels, they achieved a “raw” bitrate of 512 Gb / s, which, after subtracting the overhead data into error correction codes, gave 406.6 Gb / s. The signal was transmitted through a cable consisting of 160 segments of 80 kilometers each, between which there were only EDFA optical amplifiers.


a. The scheme of the experimental setup. b. Comparison of signal quality with and without new noise reduction circuit. with. The number of errors in the signal, the past 12800 km before and after error correction.
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The technology, called PCTW ( Phase-Conjugated Twin Waves ), will reduce the number of repeaters at long distances or even completely abandon them, leaving only amplifiers. This can significantly reduce the cost of laying transcontinental fiber-optic communication lines. At short distances, it is possible to reduce the overhead of error correction codes and increase bandwidth.