QAM Vector Signal Generation by Optical Carrier Suppression and Precoding Techniques

We numerically and experimentally investigate and compare photonic constant- and multi-amplitude quadrature-amplitude-modulation (QAM) vector signal generation at radio frequency (RF) bands enabled by a Mach-Zehnder modulator (MZM)-based optical carrier suppression (OCS) modulation. In order to attain an electrical vector RF signal displaying multi-amplitude QAM modulation, such as 8 QAM and 16 QAM, after square-law photodiode detection, the driving RF signal carrying multiamplitude QAM transmitter data, should be both amplitude- and phase-precoded before used to drive the MZM. However, for constant-amplitude QAM modulation, such as quadrature-phase-shift-keying (QPSK), only phase precoding is needed. We experimentally demonstrate 1-GBd vector signal generation at 12 GHz enabled by an MZM-based OSC modulation, adopting QPSK, 8 QAM, and 16 QAM modulation, respectively. We also experimentally compare the bit error rate performance of the three different vector signals, and the QPSK case is the best, while the 16 QAM case is the worst.