Nonlinear tolerant and spectrally efficient 86 Gbit/s RZ-DQPSK format for a system upgrade

We propose a method employing 86 Gbit/s RZ-DQPSK format to enable doubling the capacity of 43 Gbit/s WDM systems. Its relaxed OSNR, chromatic dispersion and PMD requirements allow the upgrade without changing WDM optics, using 43 Gbit/s electronics.