Viterbi-Equalizer for 40 Gbit/s Optical Communication Links

In current optical Wide-Area-Networks the bit rate is 10 Gbit/s per wavelength (2005). As broadband connections with ever higher bit rate are introduced in private households, too, the bit rate in the core network must also be increased to meet the requirements of new application fields such as IPTV. The single channel bitrate of next generation long haul optical links will be 40 Gbit/s. On such data rates the intersymbol interference caused by chromatic dispersion and polarization mode dispersion in optical fibers is a big problem.

An electronic equalizer according to the maximum likelihood sequence estimation (MLSE) method can be a solution for this problem. To realize the MLSE method the Viterbi-Algorithm is applied.
The Viterbi-Algorithm consists of many additions and comparisons (Add-Compare-Select- (ACS-) operations) which cannot be executed on these high data rates in up-to-date CMOS technologies. Therefore the Viterbi-Algorithm must be parallelized.
The aim of this work at the INT is to realize a Viterbi-Equalizer with a bit error rate of 1·10^-3 whereas the input data of the pre-processing analog-to-digital converter has a resolution of 3 bit.
The Viterbi-Equalizer-Chip have been already realized and successfully measured within an industrial liaison with Alcatel-Lucent in a 90 nm CMOS technology