High-Speed 340 Gbps PAM4 and 450 Gbps PAM6 Operations of Narrow High-Mesa EML

The volume of data traffic has been consistently increasing, especially with the development of artificial intelligence and machine learning. Consequently, the volume of data traffic in data centers has experienced exponential growth. The electro-absorption modulator integrated laser (EML) has become a mainstream technology for the intensity modulation and direct detection (IM-DD) transmitters in data centers. We developed a high-speed EML with a hybrid waveguide structure. This EML features a unique hybrid waveguide structure, which combines a buried heterostructure (BH) distributed feedback laser diode (DFB-LD), a high-mesa electro-absorption modulator (EAM) waveguide, and a spot-size converter (SSC) monolithically integrated on an n-InP substrate. In this work, we improved the 3-dB bandwidth of the EML on the sub-mount by reducing the width of the high-mesa EAM and shortening the signal wire between the EAM and the sub-mount. As a result, we achieved a 3-dB bandwidth of 106 GHz at a temperature of 40°C. The improved bandwidth enabled us to operate the narrow high-mesa EML at 340 Gbps (170 Gbaud PAM4) with a transmitter and dispersion eye closure quaternary (TDECQ) of less than 3.9 dB and at 450 Gbps (175 Gbaud PAM6). Our results should contribute to the development of transmissions beyond 200 Gbps, such as 300 Gbps and 400 Gbps per lane with FEC using IM-DD in various fields.