Improvement of Optical NRZ- and RZ-Duobinary Transmission Systems With Narrow Bandwidth Optical Filters

We show that a narrow bandwidth optical filter at the receiver side can greatly improve the receiver sensitivity of a nonreturn-to-zero (NRZ)-duobinary system. We propose to use the narrow bandwidth filtering at the receiver side of a return-to-zero (RZ)-duobinary system to convert RZ-duobinary to NRZ-duobinary, so that the system tolerance to residual chromatic dispersion can be increased while its resistance to nonlinearity in transmission is still maintained. The idea is demonstrated with experiments.