Effect of Mach-Zehnder modulator DC extinction ratio on residual chirp-induced dispersion in 10-Gb/s binary and AM-PSK duobinary lightwave systems

It is shown through numerical simulation that residual frequency chirping in lithium niobate external modulators, which accompanies devices with a finite-optical extinction ratio, always degrades the performance of lightwave systems that use optical AM-PSK duobinary signaling. This is unlike binary systems which will exhibit either an improvement or degradation, depending on the polarity of residual chirp.