42.7-Gb/s cost-effective duobinary optical transmitter using a commercial 10-Gb/s Mach-Zehnder modulator with optical filtering

Optical duobinary transmission at 42.7 Gb/s is demonstrated using a commercially available 10-Gb/s LiNbO₃ modulator. The intrinsic response of the 10-Gb/s electrooptic Mach-Zehnder modulator (MZM) is used to create a low-pass-filtered (LPF) duobinary signal, which shows a minimum optical signal-to-noise ratio (OSNR) requirement penalty of ∼4 to ∼6 dB as compared to nonreturn-to-zero (NRZ) signals. However, when the MZM-LPF duobinary is filtered with a 50-GHz 3-dB bandwidth first-order Gaussian filter, a significant improvement in required OSNR is seen. In contrast, similar optical filtering of NRZ data creates a significant OSNR penalty such that the NRZ and MZM-LPF duobinary data have nearly identical OSNR requirements. Therefore, the MZM-LPF duobinary technique may be a cost-effective approach to high-spectral-efficiency transmission at 42.7 Gb/s.