Due to the doubling of the internet traffic every twelve month and upgrading existing optical metro-, regio- and long haul
transport networks, the migration from existing networks toward high speed optical networks with channel data rates up
to 100 Gbit/s/λ is one of the most important questions today and in the near future. Current WDM Systems in photonic
networks are commonly operated at linerates of 2.5 and 10 Gbit/s/λ and major carriers already started the deployment of
40 Gbit/s/λ services. Due to the inherent increase of the bandwidth per channel, limitations due to linear and non-linear
transmission impairments become stronger resulting in a highly increased complexity of link engineering, potentially
increasing the operational expenditures (OPEX). Researchers, system vendors and -operators focus on investigations,
targeting the relaxation of constraints for 100 Gbit/s transmission to find the most efficient upgrade strategies.
The approaches towards increased robustness against signal distortions are the transmission of the 100 Gbit/s data signals
via multiple fibers, wavelength, subcarriers or the introduction of more advanced modulation formats. Different
modulation schemes and reduced baud rates show strongly different optical WDM transmission characteristics. The
choice of the appropriate format does not only depend on the technical requirements, but also on economical
considerations as an increased transmitter- and receiver-complexity will drive the transponder price.
This article presents investigations on different approaches for the upgrade of existing metro-/ regio and long haul
transport networks. The robustness against the main degrading physical effects and economy of scale are considered for
different mitigation strategies.