Silicon photonic modulators for PAM transmissions

High-speed optical interconnects are crucial for both data centers and high performance computing systems. High power consumption and limited device bandwidth have hindered the move to higher optical transmission speeds. Integrated optical transceivers in silicon photonics (SiP) using pulse-amplitude modulation (PAM) are a promising solution to increase data rates. In this paper, we review recent progress in SiP for PAM transmissions. We focus on materials and technologies available CMOS-compatible photonics processes. Performance metrics of SiP modulators and crucial considerations for high-speed PAM transmissions are discussed. Various driving strategies to achieve optical PAM signals are presented. Some of the state-of-the-art SiP PAM modulators and integrated transmitters are reviewed.