Transmitter Compliance Metric Based on PAM-4 Duobinary Feedforward Equalization

The transmitter and dispersion eye closure quaternary (TDECQ) parameter for four-level amplitude modulation (PAM-4) systems assumes a reference receiver based on a linear feedforward equalizer (FFE). However, it is expected that for future generations of optical transceivers, as the symbol rate increases, a simple full-response FFE (FR-FFE) will not be able to reach the forward error correction (FEC) limit. A linear duobinary FFE (DB-FFE) can significantly improve performance under severe bandwidth limitations and might be used in the reference receiver. In this Letter, we present a novel transmitter compliance metric based on duobinary feedforward equalization. The method uses the standardized stress sequence and requires only minor changes to the standardized TDECQ computation. The metric provides excellent accuracy in severely bandwidth-limited optical systems affected by chromatic dispersion (CD). The maximum observed TDECQ estimation error in the CD range from -40 ps/nm to 10 ps/nm with the chirped transmitter is below 0.45 dB.