Analog PAM4 modulation technique enabled by a polarization multiplexing modulator

In this paper, we propose a new method to generate radio-frequency (RF) pulse-amplitude-modulation with four amplitude levels (PAM4) signals. This method is a cost-effective one without the use of expensive digital to analog converters (DACs). By using a polarization multiplexing modulator that integrates two polarization orthogonal intensity modulators, the two polarization orthogonal intensity modulators are driven by two levels of RF signals, respectively. Then, by cascading a polarization controller (PC) and a polarizer, RF PAM4 optical signals can be generated. Based on our proposed scheme, we experimentally demonstrate the generation of RF PAM4 signal at 9.07GHz. Our experimental results show that the RF PAM4 signals have no obvious deterioration after transmission over 80km single mode fiber (SMF).