A 50Gb/s PAM-4 Bi-Directional Plastic Waveguide Link with Carrier Synchronization Using PI-Based Costas Loop

Abstract

The demand for greater I/O bandwidth in data centers is increasing due to the explosive growth of network traffic. However, conventional high-speed interconnects are struggling with the challenges in both functional and economical aspects. Copper-based electrical links are displaying their critical bandwidth limitation caused by skin loss. Optical links require significant capital expenses for the E/O and O/E conversion devices and the chip-to-fiber assembly in short-reach high-volume links. As an alternative, the recent studies present that the plastic waveguide links showing the inherent low-loss and wideband channel characteristics can be a promising solution to provide the power-/cost-efficient high-speed interconnects. However, prior arts have demonstrated only a single waveguide transmission due to the low confinement of the waveguide [1]-[4] and a limited carrier synchronization requiring external local oscillator (LO) phase tuning [2]-[4]. In this paper, we demonstrate a 1m 50Gb/s PAM-4 bi-directional plastic waveguide link with carrier synchronization using 70GHz transmitter (TX) and receiver (RX) ICs in fan-out wafer-level packaging (FOWLP) fabricated in 28nm CMOS. The link achieves an FoM of 2.8pJ/b/m showing state-of-the-art performance in terms of throughput-distance, and energy efficiency.