Investigation of transmission performance of 40-gb/s conventional DCS-RZ signals and DCS-RZ signals generated from phase-modulated duobinary signals

A 40-Gb/s duobinary carrier-suppressed return-to-zero (DCS-RZ) signal format generated from phase-modulated (PM) duobinary signals by using a phase modulator and an external intensity modulator is proposed. The transmission performance of the proposed DCS-RZ format is theoretically investigated. The proposed DCS-RZ format can produce a signal bandwidth similar to that produced by the conventional DCS-RZ format generated from conventional duobinary signals using low-pass filters. However, the receiver sensitivities of the proposed DCS-RZ format can be improved by about 2 dB more than those of the conventional DCS-RZ format due to high extinction ratio and nonlinear tolerance. Due to a short pulse of the proposed DCS-RZ format, the tolerance of the first-order polarization mode dispersion (PMD) for the format can be improved by about 1 dB up to the differential-group-delay (DGD) value of 16 ps