Bell Labs Boost Fibre Optic Speeds to 400Gbps Using Phase Conjugation

Bell Labs, the New Jersey (USA) based research and development subsidiary of telecoms giant Alcatel-Lucent, has found a way of boosting data speeds down fibre optic cables by using two light beams in opposing phases to cancel out interference that would ordinarily slow the transfer.

The method, which is in principal vaguely similar to the noise cancellation technology used in some headphones (or vectoring on copper VDSL2 (FTTC) lines), allowed the researchers to transmit information at a speed of 400Gbps (Gigabits per second) down a 12,800km long super-channel fibre optic cable.

Extract from Nature Photonics

Kerr nonlinearity imposes a limit on the achievable transmission performance and capacity of optical fibre communication links. We show that the nonlinear distortions of a pair of phase-conjugated twin waves are essentially anti-correlated, so cancellation of signal-to-signal nonlinear interactions can be achieved by coherently superimposing the twin waves at the end of the transmission line.

We demonstrate that by applying this approach to fibre communication, nonlinear distortions can be reduced by >8.5 dB.

The idea of using Optical Phase Conjugation to tackle interference has actually been around for quite a while (I can recall reading about it 15 years ago) but as ever it can take time to turn such concepts into engineered reality.

Never the less this development, if it can be turned into a commercially viable upgrade, could one day join many other recent improvements (hollow fibres etc.) in helping to boost the global data capacity of fibre optic connections (especially the international undersea links).

After all it’s often better to upgrade an existing link than to deploy another expensive cable across the ocean.