Efficient DC-coupled linear 60-GBd EML-based O-band transmitter

O-band transmitters are key to current and next-generation communication links. In this paper, the authors present a transmitter based on an InGaAlAs multi-quantum well (MQW) electroabsorption modulated laser (EML) and a 130 nm SiGe BiCMOS driver integrated circuit (IC). The functionality and architecture of both ICs are discussed, including the co-design aspects deriving from the DC-coupled interface, with a particular focus on the driver's high immunity to the EAM photocurrent and capability to supply a very wide bias voltage range to the EAM. The proposed transmitter is able to send 60 GBd PAM4 signals with an extinction ratio (ER) of 8 dB at a power efficiency of 4.3 pJ/bit. Additionally, it is able to transmit up to 80 GBd NRZ signals and is even sufficiently linear to transmit PAM8 signals at 40 GBd, showcasing the transmitter potential in a wide range of applications.