Symmetry requirements for 10-Gb/s optical duobinary transmitters

We report design guidelines for external modulator transmitter parameters such as modulator offset, modulation amplitude, chirp, and nonideal driver electronics. Binary and duobinary transmitters are found to have large differences in design tolerances. The dispersion tolerance in the optical duobinary system rely on the symmetry in signal and modulator, causing a reduced tolerance on parameters breaking this symmetry. In particular, differences in the frequency response in the two arms of the modulator are found to be much more critical in duobinary systems as compared to binary systems.