Contents 1. Introduction
The demand for higher speed in data communications systems is explosively increasing in bandwidth-hungry application fields, such as inter- and intra-data-center networks. In the forthcoming 400-Gb/s Ethernet (400GbE) transceivers for ~10-km reach, an x 50-Gbit/s/ 4-level pulse amplitude modulation (PAM4) system will be employed [1], [2]. To reduce the complexity, size, power consumption, and cost of the transceiver, systems with higher per-lane data rates and thus smaller numbers of optical lanes are strongly desired. To achieve such systems with simple intensity-modulated direct-detected (IMDD) configurations, optical components with broad modulation bandwidths are essential. PAM4 transmissions at 100 Gbit/s/ have been reported in various papers [1], [3], [4]. However, 200-Gbit/s/ remains a challenging target.
