Improved chromatic dispersion tolerance for optical duobinary transmission using coherent detection

The impact of chromatic dispersion on the complex electric field of an optical phase-coded duobinary signal is investigated through numerical simulation. Dispersion causes distortion and rotation of the optical constellation with increasing transmission distance, leading to eye closure of the received signal. When direct detection is employed, rapid eye closure starts after approximately 213 km. Employing coherent detection increases this dispersion limit by 70 km.