At the 32nd European Conference and Exhibition on Optical Communication (ECOC) 2006 the major scientific European conference on Optics for telecommunications, Alcatel confirmed it’s leading research position with more than 30 papers accepted. Alcatel’s merits of were acknowledged by the ECOC’06 technical Committee in the highly-selective post-deadline session with four top-level results on advanced technologies for future optical networks. One of the most promising result comes from a world premiere consisting in a "Transmission of 40Gbit/s QPSK with coherent detection over ultra-long distance improved by nonlinearity mitigation" obtained by Alcatel’s research team.

Optical coherent detection re-born, thanks to Alcatel Research

Coherent detection is a technique which has been successfully used in many fields of telecommunications, because of its ability to fully recover the characteristics of a signal, namely not only its amplitude but also its phase. For optical telecommunication systems, though, research on coherent detection almost stopped at the beginning of the 1990’s. At the time, the recovery of the amplitude and phase was a unique way to better detect a signal after propagation over long distances, where the signal power can be extremely low. However, the invention of the optical amplifier in the early 1990’s made it easy to bring the signal power back to more manageable values. Hence, the main application field of coherent detection faded away, until very recently.

A team from Alcatel Research has just revived the interest for optical coherent detection. The rapid progress of digital signal processors has opened tremendous opportunities for coherent detection. The real time recovery of the intensity and the phase brings unique insight on the impairments caused by propagation into the fibre. Thus, solutions to contain these impairments can be implemented digitally, allowing longer error-free distances and higher bit-rates.

Thanks to coherent-detection-enabled digital processing, the team from Alcatel obtained a significant improvement in performance after transmission over 3,000km of fibre. The team demonstrated that the distortions affecting optical data at 40Gbit/s could be mitigated noticeably. The demonstration paves the way for longer reach and higher capacity optical systems.

Three additional top-level results have been to be highlighted, covering advanced technologies for future and high-performance networks.

These world premieres cover the mitigation of the Polarisation Mode Dispersion bottleneck at 43Gb/s, the first system operation in a WDM environment of a Raman amplifier based on Photonic Crystal Fiber with a Raman coefficient well better than the state of the art conventional highly nonlinear fibres, and a new advanced 10Gb/s Coolerless Lasers with straightforward application to access networks thanks to the use of ‘Quantum Dots’ in place of standard ‘Quantum Well.