DWDM networks have been evolving to higher spectral efficiency. To make optical duobinary format,
which is considered as a suitable modulation format in MAN DWDM networks, can work in 50GHz
channel spacing 43Gb/s DWDM networks is very significant. In this paper, it is pointed out that the
delay time in delay-and-add optical duobinary system is one of key factors which affect system
performance. The suitable delay time for 43Gb/s systems compatible 50GHz with 100GHz channel
spacing is obtained by system simulation. The simulation results show that 0.8 bit delay time is more
suitable for 43Gb/s ODB DWDM system at compatible 50 with 100GHz channel spacing than 1 bit delay
time because of its higher Q value and bigger dispersion and nonlinearity tolerance.